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nfsd4: simplify stateid generation code, fix wraparound 

Follow the recommendation from rfc3530bis for stateid generation number
wraparound, simplify some code, and fix or remove incorrect comments.

Signed-off-by: J. Bruce Fields <bfields@redhat.com>
This commit is contained in:
J. Bruce Fields 2011-08-23 11:03:29 -04:00
parent b79abaddfe
commit 81b829655d
2 changed files with 26 additions and 29 deletions
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52
fs/nfsd/nfs4state.c
View File

@ -3168,6 +3168,12 @@ grace_disallows_io(struct inode *inode)
return locks_in_grace() && mandatory_lock(inode);
}
/* Returns true iff a is later than b: */
static bool stateid_generation_after(stateid_t *a, stateid_t *b)
{
return (s32)a->si_generation - (s32)b->si_generation > 0;
}
static int check_stateid_generation(stateid_t *in, stateid_t *ref, bool has_session)
{
/*
@ -3175,25 +3181,25 @@ static int check_stateid_generation(stateid_t *in, stateid_t *ref, bool has_sess
* when it is zero.
*/
if (has_session && in->si_generation == 0)
goto out;
return nfs_ok;
if (in->si_generation == ref->si_generation)
return nfs_ok;
/* If the client sends us a stateid from the future, it's buggy: */
if (in->si_generation > ref->si_generation)
if (stateid_generation_after(in, ref))
return nfserr_bad_stateid;
/*
* The following, however, can happen. For example, if the
* client sends an open and some IO at the same time, the open
* may bump si_generation while the IO is still in flight.
* Thanks to hard links and renames, the client never knows what
* file an open will affect. So it could avoid that situation
* only by serializing all opens and IO from the same open
* owner. To recover from the old_stateid error, the client
* will just have to retry the IO:
* However, we could see a stateid from the past, even from a
* non-buggy client. For example, if the client sends a lock
* while some IO is outstanding, the lock may bump si_generation
* while the IO is still in flight. The client could avoid that
* situation by waiting for responses on all the IO requests,
* but better performance may result in retrying IO that
* receives an old_stateid error if requests are rarely
* reordered in flight:
*/
if (in->si_generation < ref->si_generation)
return nfserr_old_stateid;
out:
return nfs_ok;
return nfserr_old_stateid;
}
static int is_delegation_stateid(stateid_t *stateid)
@ -3353,16 +3359,9 @@ nfsd4_free_stateid(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
ret = nfserr_bad_stateid;
goto out;
}
if (stateid->si_generation != 0) {
if (stateid->si_generation < stp->st_stateid.si_generation) {
ret = nfserr_old_stateid;
goto out;
}
if (stateid->si_generation > stp->st_stateid.si_generation) {
ret = nfserr_bad_stateid;
goto out;
}
}
ret = check_stateid_generation(stateid, &stp->st_stateid, 1);
if (ret)
goto out;
if (stp->st_type == NFS4_OPEN_STID) {
ret = nfserr_locks_held;
@ -3439,11 +3438,6 @@ nfs4_preprocess_seqid_op(struct nfsd4_compound_state *cstate, u32 seqid,
return nfserr_bad_stateid;
}
/*
* We now validate the seqid and stateid generation numbers.
* For the moment, we ignore the possibility of
* generation number wraparound.
*/
if (!nfsd4_has_session(cstate) && seqid != sop->so_seqid)
goto check_replay;

3
fs/nfsd/state.h
View File

@ -293,6 +293,9 @@ static inline void
update_stateid(stateid_t *stateid)
{
stateid->si_generation++;
/* Wraparound recommendation from 3530bis-13 9.1.3.2: */
if (stateid->si_generation == 0)
stateid->si_generation = 1;
}
/* A reasonable value for REPLAY_ISIZE was estimated as follows: