Date: Fri, 17 Nov 2023 01:52:04 GMT From: Konstantin Belousov <kib@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-main@FreeBSD.org Subject: git: 22bac49b09a9 - main - vn_lock_pair(): reasonably handle vp1 == vp2 case Message-ID: <202311170152.3AH1q4hl047927@gitrepo.freebsd.org>
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The branch main has been updated by kib: URL: https://cgit.FreeBSD.org/src/commit/?id=22bac49b09a9f975330dc0d811436599ce740890 commit 22bac49b09a9f975330dc0d811436599ce740890 Author: Konstantin Belousov <kib@FreeBSD.org> AuthorDate: 2023-11-16 22:42:25 +0000 Commit: Konstantin Belousov <kib@FreeBSD.org> CommitDate: 2023-11-17 01:51:41 +0000 vn_lock_pair(): reasonably handle vp1 == vp2 case Lock the vnode in the most exclusive lock mode requested, once. All callers already ensure that vp1 != vp2 or are careful enough to only unlock once otherwise. Reviewed by: markj Sponsored by: The FreeBSD Foundation MFC after: 1 week Differential revision: https://reviews.freebsd.org/D42642 --- sys/kern/vfs_vnops.c | 41 ++++++++++++++++++++++++++++++++++++----- 1 file changed, 36 insertions(+), 5 deletions(-) diff --git a/sys/kern/vfs_vnops.c b/sys/kern/vfs_vnops.c index 27ce5401f15f..f81516608eeb 100644 --- a/sys/kern/vfs_vnops.c +++ b/sys/kern/vfs_vnops.c @@ -4042,10 +4042,10 @@ vn_lock_pair_pause(const char *wmesg) } /* - * Lock pair of vnodes vp1, vp2, avoiding lock order reversal. - * vp1_locked indicates whether vp1 is locked; if not, vp1 must be - * unlocked. Same for vp2 and vp2_locked. One of the vnodes can be - * NULL. + * Lock pair of (possibly same) vnodes vp1, vp2, avoiding lock order + * reversal. vp1_locked indicates whether vp1 is locked; if not, vp1 + * must be unlocked. Same for vp2 and vp2_locked. One of the vnodes + * can be NULL. * * The function returns with both vnodes exclusively or shared locked, * according to corresponding lkflags, and guarantees that it does not @@ -4056,12 +4056,14 @@ vn_lock_pair_pause(const char *wmesg) * * Only one of LK_SHARED and LK_EXCLUSIVE must be specified. * LK_NODDLKTREAT can be optionally passed. + * + * If vp1 == vp2, only one, most exclusive, lock is obtained on it. */ void vn_lock_pair(struct vnode *vp1, bool vp1_locked, int lkflags1, struct vnode *vp2, bool vp2_locked, int lkflags2) { - int error; + int error, locked1; MPASS(((lkflags1 & LK_SHARED) != 0) ^ ((lkflags1 & LK_EXCLUSIVE) != 0)); MPASS((lkflags1 & ~(LK_SHARED | LK_EXCLUSIVE | LK_NODDLKTREAT)) == 0); @@ -4071,6 +4073,35 @@ vn_lock_pair(struct vnode *vp1, bool vp1_locked, int lkflags1, if (vp1 == NULL && vp2 == NULL) return; + if (vp1 == vp2) { + MPASS(vp1_locked == vp2_locked); + + /* Select the most exclusive mode for lock. */ + if ((lkflags1 & LK_TYPE_MASK) != (lkflags2 & LK_TYPE_MASK)) + lkflags1 = (lkflags1 & ~LK_SHARED) | LK_EXCLUSIVE; + + if (vp1_locked) { + ASSERT_VOP_LOCKED(vp1, "vp1"); + + /* No need to relock if any lock is exclusive. */ + if ((vp1->v_vnlock->lock_object.lo_flags & + LK_NOSHARE) != 0) + return; + + locked1 = VOP_ISLOCKED(vp1); + if (((lkflags1 & LK_SHARED) != 0 && + locked1 != LK_EXCLUSIVE) || + ((lkflags1 & LK_EXCLUSIVE) != 0 && + locked1 == LK_EXCLUSIVE)) + return; + VOP_UNLOCK(vp1); + } + + ASSERT_VOP_UNLOCKED(vp1, "vp1"); + vn_lock(vp1, lkflags1 | LK_RETRY); + return; + } + if (vp1 != NULL) { if ((lkflags1 & LK_SHARED) != 0 && (vp1->v_vnlock->lock_object.lo_flags & LK_NOSHARE) != 0)
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