![Alan Stern](/assets/img/avatar_default.png)
The kernel's implementation of notifier chains is unsafe. There is no protection against entries being added to or removed from a chain while the chain is in use. The issues were discussed in this thread: http://marc.theaimsgroup.com/?l=linux-kernel&m=113018709002036&w=2 We noticed that notifier chains in the kernel fall into two basic usage classes: "Blocking" chains are always called from a process context and the callout routines are allowed to sleep; "Atomic" chains can be called from an atomic context and the callout routines are not allowed to sleep. We decided to codify this distinction and make it part of the API. Therefore this set of patches introduces three new, parallel APIs: one for blocking notifiers, one for atomic notifiers, and one for "raw" notifiers (which is really just the old API under a new name). New kinds of data structures are used for the heads of the chains, and new routines are defined for registration, unregistration, and calling a chain. The three APIs are explained in include/linux/notifier.h and their implementation is in kernel/sys.c. With atomic and blocking chains, the implementation guarantees that the chain links will not be corrupted and that chain callers will not get messed up by entries being added or removed. For raw chains the implementation provides no guarantees at all; users of this API must provide their own protections. (The idea was that situations may come up where the assumptions of the atomic and blocking APIs are not appropriate, so it should be possible for users to handle these things in their own way.) There are some limitations, which should not be too hard to live with. For atomic/blocking chains, registration and unregistration must always be done in a process context since the chain is protected by a mutex/rwsem. Also, a callout routine for a non-raw chain must not try to register or unregister entries on its own chain. (This did happen in a couple of places and the code had to be changed to avoid it.) Since atomic chains may be called from within an NMI handler, they cannot use spinlocks for synchronization. Instead we use RCU. The overhead falls almost entirely in the unregister routine, which is okay since unregistration is much less frequent that calling a chain. Here is the list of chains that we adjusted and their classifications. None of them use the raw API, so for the moment it is only a placeholder. ATOMIC CHAINS ------------- arch/i386/kernel/traps.c: i386die_chain arch/ia64/kernel/traps.c: ia64die_chain arch/powerpc/kernel/traps.c: powerpc_die_chain arch/sparc64/kernel/traps.c: sparc64die_chain arch/x86_64/kernel/traps.c: die_chain drivers/char/ipmi/ipmi_si_intf.c: xaction_notifier_list kernel/panic.c: panic_notifier_list kernel/profile.c: task_free_notifier net/bluetooth/hci_core.c: hci_notifier net/ipv4/netfilter/ip_conntrack_core.c: ip_conntrack_chain net/ipv4/netfilter/ip_conntrack_core.c: ip_conntrack_expect_chain net/ipv6/addrconf.c: inet6addr_chain net/netfilter/nf_conntrack_core.c: nf_conntrack_chain net/netfilter/nf_conntrack_core.c: nf_conntrack_expect_chain net/netlink/af_netlink.c: netlink_chain BLOCKING CHAINS --------------- arch/powerpc/platforms/pseries/reconfig.c: pSeries_reconfig_chain arch/s390/kernel/process.c: idle_chain arch/x86_64/kernel/process.c idle_notifier drivers/base/memory.c: memory_chain drivers/cpufreq/cpufreq.c cpufreq_policy_notifier_list drivers/cpufreq/cpufreq.c cpufreq_transition_notifier_list drivers/macintosh/adb.c: adb_client_list drivers/macintosh/via-pmu.c sleep_notifier_list drivers/macintosh/via-pmu68k.c sleep_notifier_list drivers/macintosh/windfarm_core.c wf_client_list drivers/usb/core/notify.c usb_notifier_list drivers/video/fbmem.c fb_notifier_list kernel/cpu.c cpu_chain kernel/module.c module_notify_list kernel/profile.c munmap_notifier kernel/profile.c task_exit_notifier kernel/sys.c reboot_notifier_list net/core/dev.c netdev_chain net/decnet/dn_dev.c: dnaddr_chain net/ipv4/devinet.c: inetaddr_chain It's possible that some of these classifications are wrong. If they are, please let us know or submit a patch to fix them. Note that any chain that gets called very frequently should be atomic, because the rwsem read-locking used for blocking chains is very likely to incur cache misses on SMP systems. (However, if the chain's callout routines may sleep then the chain cannot be atomic.) The patch set was written by Alan Stern and Chandra Seetharaman, incorporating material written by Keith Owens and suggestions from Paul McKenney and Andrew Morton. [jes@sgi.com: restructure the notifier chain initialization macros] Signed-off-by: Alan Stern <stern@rowland.harvard.edu> Signed-off-by: Chandra Seetharaman <sekharan@us.ibm.com> Signed-off-by: Jes Sorensen <jes@sgi.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
548 lines
15 KiB
C
548 lines
15 KiB
C
/*
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* linux/kernel/profile.c
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* Simple profiling. Manages a direct-mapped profile hit count buffer,
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* with configurable resolution, support for restricting the cpus on
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* which profiling is done, and switching between cpu time and
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* schedule() calls via kernel command line parameters passed at boot.
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*
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* Scheduler profiling support, Arjan van de Ven and Ingo Molnar,
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* Red Hat, July 2004
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* Consolidation of architecture support code for profiling,
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* William Irwin, Oracle, July 2004
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* Amortized hit count accounting via per-cpu open-addressed hashtables
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* to resolve timer interrupt livelocks, William Irwin, Oracle, 2004
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*/
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#include <linux/config.h>
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#include <linux/module.h>
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#include <linux/profile.h>
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#include <linux/bootmem.h>
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#include <linux/notifier.h>
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#include <linux/mm.h>
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#include <linux/cpumask.h>
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#include <linux/cpu.h>
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#include <linux/profile.h>
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#include <linux/highmem.h>
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#include <linux/mutex.h>
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#include <asm/sections.h>
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#include <asm/semaphore.h>
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struct profile_hit {
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u32 pc, hits;
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};
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#define PROFILE_GRPSHIFT 3
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#define PROFILE_GRPSZ (1 << PROFILE_GRPSHIFT)
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#define NR_PROFILE_HIT (PAGE_SIZE/sizeof(struct profile_hit))
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#define NR_PROFILE_GRP (NR_PROFILE_HIT/PROFILE_GRPSZ)
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/* Oprofile timer tick hook */
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int (*timer_hook)(struct pt_regs *) __read_mostly;
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static atomic_t *prof_buffer;
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static unsigned long prof_len, prof_shift;
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static int prof_on __read_mostly;
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static cpumask_t prof_cpu_mask = CPU_MASK_ALL;
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#ifdef CONFIG_SMP
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static DEFINE_PER_CPU(struct profile_hit *[2], cpu_profile_hits);
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static DEFINE_PER_CPU(int, cpu_profile_flip);
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static DEFINE_MUTEX(profile_flip_mutex);
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#endif /* CONFIG_SMP */
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static int __init profile_setup(char * str)
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{
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static char __initdata schedstr[] = "schedule";
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int par;
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if (!strncmp(str, schedstr, strlen(schedstr))) {
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prof_on = SCHED_PROFILING;
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if (str[strlen(schedstr)] == ',')
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str += strlen(schedstr) + 1;
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if (get_option(&str, &par))
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prof_shift = par;
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printk(KERN_INFO
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"kernel schedule profiling enabled (shift: %ld)\n",
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prof_shift);
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} else if (get_option(&str, &par)) {
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prof_shift = par;
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prof_on = CPU_PROFILING;
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printk(KERN_INFO "kernel profiling enabled (shift: %ld)\n",
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prof_shift);
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}
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return 1;
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}
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__setup("profile=", profile_setup);
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void __init profile_init(void)
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{
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if (!prof_on)
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return;
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/* only text is profiled */
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prof_len = (_etext - _stext) >> prof_shift;
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prof_buffer = alloc_bootmem(prof_len*sizeof(atomic_t));
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}
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/* Profile event notifications */
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#ifdef CONFIG_PROFILING
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static BLOCKING_NOTIFIER_HEAD(task_exit_notifier);
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static ATOMIC_NOTIFIER_HEAD(task_free_notifier);
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static BLOCKING_NOTIFIER_HEAD(munmap_notifier);
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void profile_task_exit(struct task_struct * task)
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{
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blocking_notifier_call_chain(&task_exit_notifier, 0, task);
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}
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int profile_handoff_task(struct task_struct * task)
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{
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int ret;
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ret = atomic_notifier_call_chain(&task_free_notifier, 0, task);
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return (ret == NOTIFY_OK) ? 1 : 0;
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}
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void profile_munmap(unsigned long addr)
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{
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blocking_notifier_call_chain(&munmap_notifier, 0, (void *)addr);
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}
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int task_handoff_register(struct notifier_block * n)
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{
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return atomic_notifier_chain_register(&task_free_notifier, n);
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}
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int task_handoff_unregister(struct notifier_block * n)
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{
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return atomic_notifier_chain_unregister(&task_free_notifier, n);
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}
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int profile_event_register(enum profile_type type, struct notifier_block * n)
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{
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int err = -EINVAL;
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switch (type) {
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case PROFILE_TASK_EXIT:
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err = blocking_notifier_chain_register(
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&task_exit_notifier, n);
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break;
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case PROFILE_MUNMAP:
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err = blocking_notifier_chain_register(
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&munmap_notifier, n);
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break;
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}
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return err;
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}
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int profile_event_unregister(enum profile_type type, struct notifier_block * n)
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{
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int err = -EINVAL;
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switch (type) {
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case PROFILE_TASK_EXIT:
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err = blocking_notifier_chain_unregister(
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&task_exit_notifier, n);
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break;
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case PROFILE_MUNMAP:
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err = blocking_notifier_chain_unregister(
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&munmap_notifier, n);
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break;
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}
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return err;
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}
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int register_timer_hook(int (*hook)(struct pt_regs *))
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{
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if (timer_hook)
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return -EBUSY;
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timer_hook = hook;
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return 0;
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}
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void unregister_timer_hook(int (*hook)(struct pt_regs *))
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{
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WARN_ON(hook != timer_hook);
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timer_hook = NULL;
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/* make sure all CPUs see the NULL hook */
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synchronize_sched(); /* Allow ongoing interrupts to complete. */
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}
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EXPORT_SYMBOL_GPL(register_timer_hook);
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EXPORT_SYMBOL_GPL(unregister_timer_hook);
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EXPORT_SYMBOL_GPL(task_handoff_register);
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EXPORT_SYMBOL_GPL(task_handoff_unregister);
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#endif /* CONFIG_PROFILING */
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EXPORT_SYMBOL_GPL(profile_event_register);
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EXPORT_SYMBOL_GPL(profile_event_unregister);
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#ifdef CONFIG_SMP
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/*
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* Each cpu has a pair of open-addressed hashtables for pending
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* profile hits. read_profile() IPI's all cpus to request them
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* to flip buffers and flushes their contents to prof_buffer itself.
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* Flip requests are serialized by the profile_flip_mutex. The sole
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* use of having a second hashtable is for avoiding cacheline
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* contention that would otherwise happen during flushes of pending
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* profile hits required for the accuracy of reported profile hits
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* and so resurrect the interrupt livelock issue.
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*
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* The open-addressed hashtables are indexed by profile buffer slot
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* and hold the number of pending hits to that profile buffer slot on
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* a cpu in an entry. When the hashtable overflows, all pending hits
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* are accounted to their corresponding profile buffer slots with
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* atomic_add() and the hashtable emptied. As numerous pending hits
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* may be accounted to a profile buffer slot in a hashtable entry,
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* this amortizes a number of atomic profile buffer increments likely
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* to be far larger than the number of entries in the hashtable,
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* particularly given that the number of distinct profile buffer
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* positions to which hits are accounted during short intervals (e.g.
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* several seconds) is usually very small. Exclusion from buffer
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* flipping is provided by interrupt disablement (note that for
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* SCHED_PROFILING profile_hit() may be called from process context).
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* The hash function is meant to be lightweight as opposed to strong,
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* and was vaguely inspired by ppc64 firmware-supported inverted
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* pagetable hash functions, but uses a full hashtable full of finite
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* collision chains, not just pairs of them.
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*
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* -- wli
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*/
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static void __profile_flip_buffers(void *unused)
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{
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int cpu = smp_processor_id();
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per_cpu(cpu_profile_flip, cpu) = !per_cpu(cpu_profile_flip, cpu);
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}
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static void profile_flip_buffers(void)
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{
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int i, j, cpu;
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mutex_lock(&profile_flip_mutex);
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j = per_cpu(cpu_profile_flip, get_cpu());
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put_cpu();
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on_each_cpu(__profile_flip_buffers, NULL, 0, 1);
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for_each_online_cpu(cpu) {
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struct profile_hit *hits = per_cpu(cpu_profile_hits, cpu)[j];
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for (i = 0; i < NR_PROFILE_HIT; ++i) {
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if (!hits[i].hits) {
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if (hits[i].pc)
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hits[i].pc = 0;
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continue;
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}
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atomic_add(hits[i].hits, &prof_buffer[hits[i].pc]);
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hits[i].hits = hits[i].pc = 0;
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}
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}
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mutex_unlock(&profile_flip_mutex);
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}
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static void profile_discard_flip_buffers(void)
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{
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int i, cpu;
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mutex_lock(&profile_flip_mutex);
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i = per_cpu(cpu_profile_flip, get_cpu());
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put_cpu();
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on_each_cpu(__profile_flip_buffers, NULL, 0, 1);
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for_each_online_cpu(cpu) {
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struct profile_hit *hits = per_cpu(cpu_profile_hits, cpu)[i];
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memset(hits, 0, NR_PROFILE_HIT*sizeof(struct profile_hit));
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}
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mutex_unlock(&profile_flip_mutex);
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}
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void profile_hit(int type, void *__pc)
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{
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unsigned long primary, secondary, flags, pc = (unsigned long)__pc;
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int i, j, cpu;
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struct profile_hit *hits;
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if (prof_on != type || !prof_buffer)
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return;
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pc = min((pc - (unsigned long)_stext) >> prof_shift, prof_len - 1);
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i = primary = (pc & (NR_PROFILE_GRP - 1)) << PROFILE_GRPSHIFT;
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secondary = (~(pc << 1) & (NR_PROFILE_GRP - 1)) << PROFILE_GRPSHIFT;
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cpu = get_cpu();
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hits = per_cpu(cpu_profile_hits, cpu)[per_cpu(cpu_profile_flip, cpu)];
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if (!hits) {
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put_cpu();
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return;
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}
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local_irq_save(flags);
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do {
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for (j = 0; j < PROFILE_GRPSZ; ++j) {
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if (hits[i + j].pc == pc) {
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hits[i + j].hits++;
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goto out;
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} else if (!hits[i + j].hits) {
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hits[i + j].pc = pc;
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hits[i + j].hits = 1;
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goto out;
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}
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}
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i = (i + secondary) & (NR_PROFILE_HIT - 1);
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} while (i != primary);
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atomic_inc(&prof_buffer[pc]);
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for (i = 0; i < NR_PROFILE_HIT; ++i) {
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atomic_add(hits[i].hits, &prof_buffer[hits[i].pc]);
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hits[i].pc = hits[i].hits = 0;
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}
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out:
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local_irq_restore(flags);
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put_cpu();
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}
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#ifdef CONFIG_HOTPLUG_CPU
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static int __devinit profile_cpu_callback(struct notifier_block *info,
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unsigned long action, void *__cpu)
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{
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int node, cpu = (unsigned long)__cpu;
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struct page *page;
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switch (action) {
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case CPU_UP_PREPARE:
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node = cpu_to_node(cpu);
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per_cpu(cpu_profile_flip, cpu) = 0;
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if (!per_cpu(cpu_profile_hits, cpu)[1]) {
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page = alloc_pages_node(node, GFP_KERNEL | __GFP_ZERO, 0);
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if (!page)
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return NOTIFY_BAD;
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per_cpu(cpu_profile_hits, cpu)[1] = page_address(page);
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}
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if (!per_cpu(cpu_profile_hits, cpu)[0]) {
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page = alloc_pages_node(node, GFP_KERNEL | __GFP_ZERO, 0);
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if (!page)
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goto out_free;
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per_cpu(cpu_profile_hits, cpu)[0] = page_address(page);
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}
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break;
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out_free:
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page = virt_to_page(per_cpu(cpu_profile_hits, cpu)[1]);
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per_cpu(cpu_profile_hits, cpu)[1] = NULL;
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__free_page(page);
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return NOTIFY_BAD;
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case CPU_ONLINE:
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cpu_set(cpu, prof_cpu_mask);
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break;
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case CPU_UP_CANCELED:
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case CPU_DEAD:
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cpu_clear(cpu, prof_cpu_mask);
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if (per_cpu(cpu_profile_hits, cpu)[0]) {
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page = virt_to_page(per_cpu(cpu_profile_hits, cpu)[0]);
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per_cpu(cpu_profile_hits, cpu)[0] = NULL;
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__free_page(page);
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}
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if (per_cpu(cpu_profile_hits, cpu)[1]) {
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page = virt_to_page(per_cpu(cpu_profile_hits, cpu)[1]);
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per_cpu(cpu_profile_hits, cpu)[1] = NULL;
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__free_page(page);
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}
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break;
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}
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return NOTIFY_OK;
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}
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#endif /* CONFIG_HOTPLUG_CPU */
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#else /* !CONFIG_SMP */
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#define profile_flip_buffers() do { } while (0)
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#define profile_discard_flip_buffers() do { } while (0)
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void profile_hit(int type, void *__pc)
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{
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unsigned long pc;
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if (prof_on != type || !prof_buffer)
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return;
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pc = ((unsigned long)__pc - (unsigned long)_stext) >> prof_shift;
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atomic_inc(&prof_buffer[min(pc, prof_len - 1)]);
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}
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#endif /* !CONFIG_SMP */
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void profile_tick(int type, struct pt_regs *regs)
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{
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if (type == CPU_PROFILING && timer_hook)
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timer_hook(regs);
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if (!user_mode(regs) && cpu_isset(smp_processor_id(), prof_cpu_mask))
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profile_hit(type, (void *)profile_pc(regs));
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}
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#ifdef CONFIG_PROC_FS
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#include <linux/proc_fs.h>
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#include <asm/uaccess.h>
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#include <asm/ptrace.h>
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static int prof_cpu_mask_read_proc (char *page, char **start, off_t off,
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int count, int *eof, void *data)
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{
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int len = cpumask_scnprintf(page, count, *(cpumask_t *)data);
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if (count - len < 2)
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return -EINVAL;
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len += sprintf(page + len, "\n");
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return len;
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}
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static int prof_cpu_mask_write_proc (struct file *file, const char __user *buffer,
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unsigned long count, void *data)
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{
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cpumask_t *mask = (cpumask_t *)data;
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unsigned long full_count = count, err;
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cpumask_t new_value;
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err = cpumask_parse(buffer, count, new_value);
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if (err)
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return err;
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*mask = new_value;
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return full_count;
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}
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void create_prof_cpu_mask(struct proc_dir_entry *root_irq_dir)
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{
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struct proc_dir_entry *entry;
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/* create /proc/irq/prof_cpu_mask */
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if (!(entry = create_proc_entry("prof_cpu_mask", 0600, root_irq_dir)))
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return;
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entry->nlink = 1;
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entry->data = (void *)&prof_cpu_mask;
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entry->read_proc = prof_cpu_mask_read_proc;
|
|
entry->write_proc = prof_cpu_mask_write_proc;
|
|
}
|
|
|
|
/*
|
|
* This function accesses profiling information. The returned data is
|
|
* binary: the sampling step and the actual contents of the profile
|
|
* buffer. Use of the program readprofile is recommended in order to
|
|
* get meaningful info out of these data.
|
|
*/
|
|
static ssize_t
|
|
read_profile(struct file *file, char __user *buf, size_t count, loff_t *ppos)
|
|
{
|
|
unsigned long p = *ppos;
|
|
ssize_t read;
|
|
char * pnt;
|
|
unsigned int sample_step = 1 << prof_shift;
|
|
|
|
profile_flip_buffers();
|
|
if (p >= (prof_len+1)*sizeof(unsigned int))
|
|
return 0;
|
|
if (count > (prof_len+1)*sizeof(unsigned int) - p)
|
|
count = (prof_len+1)*sizeof(unsigned int) - p;
|
|
read = 0;
|
|
|
|
while (p < sizeof(unsigned int) && count > 0) {
|
|
put_user(*((char *)(&sample_step)+p),buf);
|
|
buf++; p++; count--; read++;
|
|
}
|
|
pnt = (char *)prof_buffer + p - sizeof(atomic_t);
|
|
if (copy_to_user(buf,(void *)pnt,count))
|
|
return -EFAULT;
|
|
read += count;
|
|
*ppos += read;
|
|
return read;
|
|
}
|
|
|
|
/*
|
|
* Writing to /proc/profile resets the counters
|
|
*
|
|
* Writing a 'profiling multiplier' value into it also re-sets the profiling
|
|
* interrupt frequency, on architectures that support this.
|
|
*/
|
|
static ssize_t write_profile(struct file *file, const char __user *buf,
|
|
size_t count, loff_t *ppos)
|
|
{
|
|
#ifdef CONFIG_SMP
|
|
extern int setup_profiling_timer (unsigned int multiplier);
|
|
|
|
if (count == sizeof(int)) {
|
|
unsigned int multiplier;
|
|
|
|
if (copy_from_user(&multiplier, buf, sizeof(int)))
|
|
return -EFAULT;
|
|
|
|
if (setup_profiling_timer(multiplier))
|
|
return -EINVAL;
|
|
}
|
|
#endif
|
|
profile_discard_flip_buffers();
|
|
memset(prof_buffer, 0, prof_len * sizeof(atomic_t));
|
|
return count;
|
|
}
|
|
|
|
static struct file_operations proc_profile_operations = {
|
|
.read = read_profile,
|
|
.write = write_profile,
|
|
};
|
|
|
|
#ifdef CONFIG_SMP
|
|
static void __init profile_nop(void *unused)
|
|
{
|
|
}
|
|
|
|
static int __init create_hash_tables(void)
|
|
{
|
|
int cpu;
|
|
|
|
for_each_online_cpu(cpu) {
|
|
int node = cpu_to_node(cpu);
|
|
struct page *page;
|
|
|
|
page = alloc_pages_node(node, GFP_KERNEL | __GFP_ZERO, 0);
|
|
if (!page)
|
|
goto out_cleanup;
|
|
per_cpu(cpu_profile_hits, cpu)[1]
|
|
= (struct profile_hit *)page_address(page);
|
|
page = alloc_pages_node(node, GFP_KERNEL | __GFP_ZERO, 0);
|
|
if (!page)
|
|
goto out_cleanup;
|
|
per_cpu(cpu_profile_hits, cpu)[0]
|
|
= (struct profile_hit *)page_address(page);
|
|
}
|
|
return 0;
|
|
out_cleanup:
|
|
prof_on = 0;
|
|
smp_mb();
|
|
on_each_cpu(profile_nop, NULL, 0, 1);
|
|
for_each_online_cpu(cpu) {
|
|
struct page *page;
|
|
|
|
if (per_cpu(cpu_profile_hits, cpu)[0]) {
|
|
page = virt_to_page(per_cpu(cpu_profile_hits, cpu)[0]);
|
|
per_cpu(cpu_profile_hits, cpu)[0] = NULL;
|
|
__free_page(page);
|
|
}
|
|
if (per_cpu(cpu_profile_hits, cpu)[1]) {
|
|
page = virt_to_page(per_cpu(cpu_profile_hits, cpu)[1]);
|
|
per_cpu(cpu_profile_hits, cpu)[1] = NULL;
|
|
__free_page(page);
|
|
}
|
|
}
|
|
return -1;
|
|
}
|
|
#else
|
|
#define create_hash_tables() ({ 0; })
|
|
#endif
|
|
|
|
static int __init create_proc_profile(void)
|
|
{
|
|
struct proc_dir_entry *entry;
|
|
|
|
if (!prof_on)
|
|
return 0;
|
|
if (create_hash_tables())
|
|
return -1;
|
|
if (!(entry = create_proc_entry("profile", S_IWUSR | S_IRUGO, NULL)))
|
|
return 0;
|
|
entry->proc_fops = &proc_profile_operations;
|
|
entry->size = (1+prof_len) * sizeof(atomic_t);
|
|
hotcpu_notifier(profile_cpu_callback, 0);
|
|
return 0;
|
|
}
|
|
module_init(create_proc_profile);
|
|
#endif /* CONFIG_PROC_FS */
|