D45571.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
	@@ -4002,9 +4002,15 @@
	/*
	* With GB_NOCREAT we must be sure about not finding the buffer
	* as it may have been reassigned during unlocked lookup.
	+ * If BO_NONSTERILE is still unset, no reassign has occurred.
	*/
	- if ((flags & GB_NOCREAT) != 0)
	+ if ((flags & GB_NOCREAT) != 0) {
	+ /* Ensure bo_flag is loaded after gbincore_unlocked. */
	+ atomic_thread_fence_acq();
	+ if ((bo->bo_flag & BO_NONSTERILE) == 0)
	+ return (EEXIST);
	goto loop;
	+ }
	goto newbuf_unlocked;
	}

	diff --git a/sys/kern/vfs_subr.c b/sys/kern/vfs_subr.c
	--- a/sys/kern/vfs_subr.c
	+++ b/sys/kern/vfs_subr.c
	@@ -3207,6 +3207,16 @@
	bp, bp->b_vp, bp->b_flags);

	BO_LOCK(bo);
	+ if ((bo->bo_flag & BO_NONSTERILE) == 0) {
	+ /*
	+ * Coordinate with getblk's unlocked lookup. Make
	+ * BO_NONSTERILE visible before the first reassignbuf produces
	+ * any side effect. This could be outside the bo lock if we
	+ * used a separate atomic flag field.
	+ */
	+ bo->bo_flag \|= BO_NONSTERILE;
	+ atomic_thread_fence_rel();
	+ }
	buf_vlist_remove(bp);

	/*
	diff --git a/sys/sys/bufobj.h b/sys/sys/bufobj.h
	--- a/sys/sys/bufobj.h
	+++ b/sys/sys/bufobj.h
	@@ -116,6 +116,7 @@
	#define BO_WWAIT (1 << 1) /* Wait for output to complete */
	#define BO_DEAD (1 << 2) /* Dead; only with INVARIANTS */
	#define BO_NOBUFS (1 << 3) /* No bufs allowed */
	+#define BO_NONSTERILE (1 << 4) /* Ever called reassignbuf() */

	#define BO_LOCKPTR(bo) (&(bo)->bo_lock)
	#define BO_LOCK(bo) rw_wlock(BO_LOCKPTR((bo)))