getblk: Avoid sleeping on wrong buf in lockless path
If the buffer identity changed during lookup, sleeping could introduce a lock order reversal. Since we do not know if the identity changed until we get the lock, we must try-lock (LK_NOWAIT) only. EINTR and ERESTART error handling becomes irrelevant, as we no longer sleep. Reported by: kib Reviewed by: kib X-MFC-With: r363482 Sponsored by: Dell EMC Isilon Differential Revision: https://reviews.freebsd.org/D25898
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parent
9119bafbaf
commit
59d13f6154
Notes:
svn2git
2020-12-20 02:59:44 +00:00
svn path=/head/; revision=363721
@ -3844,7 +3844,7 @@ getblkx(struct vnode *vp, daddr_t blkno, daddr_t dblkno, int size, int slpflag,
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struct buf *bp;
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struct bufobj *bo;
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daddr_t d_blkno;
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int bsize, error, maxsize, vmio, lockflags;
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int bsize, error, maxsize, vmio;
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off_t offset;
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CTR3(KTR_BUF, "getblk(%p, %ld, %d)", vp, (long)blkno, size);
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@ -3865,14 +3865,9 @@ getblkx(struct vnode *vp, daddr_t blkno, daddr_t dblkno, int size, int slpflag,
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if (bp == NULL)
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goto newbuf_unlocked;
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lockflags = LK_EXCLUSIVE | LK_SLEEPFAIL |
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((flags & GB_LOCK_NOWAIT) ? LK_NOWAIT : 0);
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error = BUF_TIMELOCK(bp, lockflags, NULL, "getblku", slpflag,
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slptimeo);
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if (error == EINTR || error == ERESTART)
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return (error);
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else if (error != 0)
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error = BUF_TIMELOCK(bp, LK_EXCLUSIVE | LK_NOWAIT, NULL, "getblku", 0,
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0);
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if (error != 0)
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goto loop;
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/* Verify buf identify has not changed since lookup. */
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@ -3886,6 +3881,8 @@ getblkx(struct vnode *vp, daddr_t blkno, daddr_t dblkno, int size, int slpflag,
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BO_RLOCK(bo);
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bp = gbincore(bo, blkno);
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if (bp != NULL) {
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int lockflags;
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/*
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* Buffer is in-core. If the buffer is not busy nor managed,
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* it must be on a queue.
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