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vn_lock_pair(): reasonably handle vp1 == vp2 case

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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
This commit is contained in:
Konstantin Belousov 2023-11-17 00:42:25 +02:00
parent e256f71389
commit 22bac49b09
1 changed files with 36 additions and 5 deletions
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41
sys/kern/vfs_vnops.c
View file

@ -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)