D45245.diff
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	diff --git a/sys/kern/vfs_bio.c b/sys/kern/vfs_bio.c
	--- a/sys/kern/vfs_bio.c
	+++ b/sys/kern/vfs_bio.c
	@@ -4010,8 +4010,23 @@

	error = BUF_TIMELOCK(bp, LK_EXCLUSIVE \| LK_NOWAIT, NULL, "getblku", 0,
	0);
	- if (error != 0)
	+ if (error != 0) {
	+ KASSERT(error == EBUSY,
	+ ("getblk: unexpected error %d from buf try-lock", error));
	+ /*
	+ * We failed a buf try-lock.
	+ *
	+ * With GB_LOCK_NOWAIT, just return, rather than taking the
	+ * bufobj interlock and trying again, since we would probably
	+ * fail again anyway. This is okay even if the buf's identity
	+ * changed and we contended on the wrong lock, as changing
	+ * identity itself requires the buf lock, and we could have
	+ * contended on the right lock.
	+ */
	+ if ((flags & GB_LOCK_NOWAIT) != 0)
	+ return (error);
	goto loop;
	+ }

	/* Verify buf identify has not changed since lookup. */
	if (bp->b_bufobj == bo && bp->b_lblkno == blkno)
	@@ -4020,6 +4035,10 @@
	/* It changed, fallback to locked lookup. */
	BUF_UNLOCK_RAW(bp);

	+ /* As above, with GB_LOCK_NOWAIT, just return. */
	+ if ((flags & GB_LOCK_NOWAIT) != 0)
	+ return (EBUSY);
	+
	loop:
	BO_RLOCK(bo);
	bp = gbincore(bo, blkno);