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Make recursive getblk() slightly more useful. Keep the buffer state

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intact if getblk() is done on the already owned buffer.  Exit from
brelse() early when the lock recursion is detected, otherwise brelse()
might prematurely destroy the buffer under some circumstances.

Sponsored by:	The FreeBSD Foundation
Noted by:	mckusick
Tested by:	pho
MFC after:	2 weeks
This commit is contained in:
Konstantin Belousov 2013-02-27 07:34:09 +00:00
parent ba05dec5a4
commit 20f4e3e158
1 changed files with 13 additions and 6 deletions
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19
sys/kern/vfs_bio.c
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@ -1268,6 +1268,15 @@ brelse(struct buf *bp)
KASSERT(!(bp->b_flags & (B_CLUSTER|B_PAGING)),
("brelse: inappropriate B_PAGING or B_CLUSTER bp %p", bp));
if (BUF_LOCKRECURSED(bp)) {
/*
* Do not process, in particular, do not handle the
* B_INVAL/B_RELBUF and do not release to free list.
*/
BUF_UNLOCK(bp);
return;
}
if (bp->b_flags & B_MANAGED) {
bqrelse(bp);
return;
@ -1444,12 +1453,6 @@ brelse(struct buf *bp)
brelvp(bp);
}
if (BUF_LOCKRECURSED(bp)) {
/* do not release to free list */
BUF_UNLOCK(bp);
return;
}
/* enqueue */
mtx_lock(&bqlock);
/* Handle delayed bremfree() processing. */
@ -2681,6 +2684,9 @@ loop:
/* We timed out or were interrupted. */
else if (error)
return (NULL);
/* If recursed, assume caller knows the rules. */
else if (BUF_LOCKRECURSED(bp))
goto end;
/*
* The buffer is locked. B_CACHE is cleared if the buffer is
@ -2864,6 +2870,7 @@ loop:
}
CTR4(KTR_BUF, "getblk(%p, %ld, %d) = %p", vp, (long)blkno, size, bp);
BUF_ASSERT_HELD(bp);
end:
KASSERT(bp->b_bufobj == bo,
("bp %p wrong b_bufobj %p should be %p", bp, bp->b_bufobj, bo));
return (bp);