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[PATCH] uml: fix thread startup race 

This fixes a race in the starting of write_sigio_thread.  Previously, some of
the data needed by the thread was initialized after the clone.  If the thread
ran immediately, it would see the uninitialized data, including an empty
pollfds, which would cause it to hang.

We move the data initialization to before the clone, and adjust the error
paths and cleanup accordingly.

Signed-off-by: Jeff Dike <jdike@addtoit.com>
Cc: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Jeff Dike 2006-03-27 01:14:40 -08:00 committed by Linus Torvalds
parent 1fbbd6844e
commit 5f4e8fd08f
1 changed files with 28 additions and 29 deletions
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57
arch/um/os-Linux/sigio.c
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@ -29,8 +29,10 @@ static int write_sigio_pid = -1;
* the descriptors closed after it is killed. So, it can't see them change.
* On the UML side, they are changed under the sigio_lock.
*/
static int write_sigio_fds[2] = { -1, -1 };
static int sigio_private[2] = { -1, -1 };
#define SIGIO_FDS_INIT {-1, -1}
static int write_sigio_fds[2] = SIGIO_FDS_INIT;
static int sigio_private[2] = SIGIO_FDS_INIT;
struct pollfds {
struct pollfd *poll;
@ -270,7 +272,17 @@ void write_sigio_workaround(void)
/* Did we race? Don't try to optimize this, please, it's not so likely
* to happen, and no more than once at the boot. */
if(write_sigio_pid != -1)
goto out_unlock;
goto out_free;
current_poll = ((struct pollfds) { .poll = p,
.used = 1,
.size = 1 });
if (write_sigio_irq(l_write_sigio_fds[0]))
goto out_clear_poll;
memcpy(write_sigio_fds, l_write_sigio_fds, sizeof(l_write_sigio_fds));
memcpy(sigio_private, l_sigio_private, sizeof(l_sigio_private));
write_sigio_pid = run_helper_thread(write_sigio_thread, NULL,
CLONE_FILES | CLONE_VM, &stack, 0);
@ -278,41 +290,28 @@ void write_sigio_workaround(void)
if (write_sigio_pid < 0)
goto out_clear;
if (write_sigio_irq(l_write_sigio_fds[0]))
goto out_kill;
/* Success, finally. */
memcpy(write_sigio_fds, l_write_sigio_fds, sizeof(l_write_sigio_fds));
memcpy(sigio_private, l_sigio_private, sizeof(l_sigio_private));
current_poll = ((struct pollfds) { .poll = p,
.used = 1,
.size = 1 });
sigio_unlock();
return;
out_kill:
l_write_sigio_pid = write_sigio_pid;
out_clear:
write_sigio_pid = -1;
sigio_unlock();
/* Going to call waitpid, avoid holding the lock. */
os_kill_process(l_write_sigio_pid, 1);
goto out_free;
out_clear:
write_sigio_pid = -1;
out_unlock:
sigio_unlock();
out_free:
write_sigio_fds[0] = -1;
write_sigio_fds[1] = -1;
sigio_private[0] = -1;
sigio_private[1] = -1;
out_clear_poll:
current_poll = ((struct pollfds) { .poll = NULL,
.size = 0,
.used = 0 });
out_free:
kfree(p);
out_close2:
sigio_unlock();
out_close2:
close(l_sigio_private[0]);
close(l_sigio_private[1]);
out_close1:
out_close1:
close(l_write_sigio_fds[0]);
close(l_write_sigio_fds[1]);
return;
}
void sigio_cleanup(void)