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Fix for a very rare race, caused by the nfsiod wakeup and nfsiod idle

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timeout occurring at exactly the same time. If this happens, the nfsiod
exits although there may be a queued async IO request for it.

Found by : Kris Kennaway
Approved by: re
This commit is contained in:
Mohan Srinivasan 2007-09-25 21:08:49 +00:00
parent 129f717f65
commit 17c53e4a28
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=172324
2 changed files with 20 additions and 3 deletions
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7
sys/nfsclient/nfs_bio.c
View File

@ -1453,6 +1453,13 @@ nfs_asyncio(struct nfsmount *nmp, struct buf *bp, struct ucred *cred, struct thr
}
}
/* We might have lost our nfsiod */
if (nmp->nm_bufqiods == 0) {
NFS_DPF(ASYNCIO,
("nfs_asyncio: no iods after mount %p queue was drained, looping\n", nmp));
goto again;
}
if (bp->b_iocmd == BIO_READ) {
if (bp->b_rcred == NOCRED && cred != NOCRED)
bp->b_rcred = crhold(cred);

16
sys/nfsclient/nfs_nfsiod.c
View File

@ -229,9 +229,8 @@ nfssvc_iod(void *instance)
* Main loop
*/
for (;;) {
while (((nmp = nfs_iodmount[myiod]) == NULL
|| !TAILQ_FIRST(&nmp->nm_bufq))
&& error == 0) {
while (((nmp = nfs_iodmount[myiod]) == NULL)
|| !TAILQ_FIRST(&nmp->nm_bufq)) {
if (myiod >= nfs_iodmax)
goto finish;
if (nmp)
@ -244,6 +243,17 @@ nfssvc_iod(void *instance)
timo = (myiod < nfs_iodmin) ? 0 : nfs_iodmaxidle * hz;
error = msleep(&nfs_iodwant[myiod], &nfs_iod_mtx, PWAIT | PCATCH,
"-", timo);
if (error) {
nmp = nfs_iodmount[myiod];
/*
* Rechecking the nm_bufq closes a rare race where the
* nfsiod is woken up at the exact time the idle timeout
* fires
*/
if (nmp && TAILQ_FIRST(&nmp->nm_bufq))
error = 0;
break;
}
}
if (error)
break;