From 59d13f615418fab119911e8df9799303cd6be222 Mon Sep 17 00:00:00 2001 From: Conrad Meyer Date: Fri, 31 Jul 2020 00:07:01 +0000 Subject: [PATCH] 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 --- sys/kern/vfs_bio.c | 15 ++++++--------- 1 file changed, 6 insertions(+), 9 deletions(-) diff --git a/sys/kern/vfs_bio.c b/sys/kern/vfs_bio.c index 0deb5ff785c4..bf9f46b7a72a 100644 --- a/sys/kern/vfs_bio.c +++ b/sys/kern/vfs_bio.c @@ -3844,7 +3844,7 @@ getblkx(struct vnode *vp, daddr_t blkno, daddr_t dblkno, int size, int slpflag, struct buf *bp; struct bufobj *bo; daddr_t d_blkno; - int bsize, error, maxsize, vmio, lockflags; + int bsize, error, maxsize, vmio; off_t offset; CTR3(KTR_BUF, "getblk(%p, %ld, %d)", vp, (long)blkno, size); @@ -3865,14 +3865,9 @@ getblkx(struct vnode *vp, daddr_t blkno, daddr_t dblkno, int size, int slpflag, if (bp == NULL) goto newbuf_unlocked; - lockflags = LK_EXCLUSIVE | LK_SLEEPFAIL | - ((flags & GB_LOCK_NOWAIT) ? LK_NOWAIT : 0); - - error = BUF_TIMELOCK(bp, lockflags, NULL, "getblku", slpflag, - slptimeo); - if (error == EINTR || error == ERESTART) - return (error); - else if (error != 0) + error = BUF_TIMELOCK(bp, LK_EXCLUSIVE | LK_NOWAIT, NULL, "getblku", 0, + 0); + if (error != 0) goto loop; /* Verify buf identify has not changed since lookup. */ @@ -3886,6 +3881,8 @@ getblkx(struct vnode *vp, daddr_t blkno, daddr_t dblkno, int size, int slpflag, BO_RLOCK(bo); bp = gbincore(bo, blkno); if (bp != NULL) { + int lockflags; + /* * Buffer is in-core. If the buffer is not busy nor managed, * it must be on a queue.