The branch main has been updated by jah: URL: https://cgit.FreeBSD.org/src/commit/?id=42442d7a6eeb860e00f76aae5858884b44f6cce5
commit 42442d7a6eeb860e00f76aae5858884b44f6cce5 Author: Jason A. Harmening <[email protected]> AuthorDate: 2022-10-26 22:25:20 +0000 Commit: Jason A. Harmening <[email protected]> CommitDate: 2022-12-11 04:02:38 +0000 Generalize the VV_CROSSLOCK logic in vfs_lookup() When VV_CROSSLOCK is present, the lock for the vnode at the current stage of lookup must be held across the VFS_ROOT() call for the filesystem mounted at the vnode. Since VV_CROSSLOCK implies that the root vnode reuses the already-held lock, the possibility for recursion should be made clear in the flags passed to VFS_ROOT(). For cases in which the lock is held exclusive, this means passing LK_CANRECURSE. For cases in which the lock is held shared, it means clearing LK_NODDLKTREAT to allow VFS_ROOT() to potentially recurse on the shared lock even in the presence of an exclusive waiter. That the existing code works for unionfs is due to a coincidence of the current unionfs implementation. Reviewed by: kib Tested by: pho Differential Revision: https://reviews.freebsd.org/D37458 --- sys/kern/vfs_lookup.c | 30 ++++++++++++++++++++++-------- 1 file changed, 22 insertions(+), 8 deletions(-) diff --git a/sys/kern/vfs_lookup.c b/sys/kern/vfs_lookup.c index cc41849de532..404c41a1bf2c 100644 --- a/sys/kern/vfs_lookup.c +++ b/sys/kern/vfs_lookup.c @@ -1265,14 +1265,28 @@ good: crosslock = (dp->v_vflag & VV_CROSSLOCK) != 0; crosslkflags = compute_cn_lkflags(mp, cnp->cn_lkflags, cnp->cn_flags); - if (__predict_false(crosslock) && - (crosslkflags & LK_EXCLUSIVE) != 0 && - VOP_ISLOCKED(dp) != LK_EXCLUSIVE) { - vn_lock(dp, LK_UPGRADE | LK_RETRY); - if (VN_IS_DOOMED(dp)) { - error = ENOENT; - goto bad2; - } + if (__predict_false(crosslock)) { + /* + * We are going to be holding the vnode lock, which + * in this case is shared by the root vnode of the + * filesystem mounted at mp, across the call to + * VFS_ROOT(). Make the situation clear to the + * filesystem by passing LK_CANRECURSE if the + * lock is held exclusive, or by clearinng + * LK_NODDLKTREAT to allow recursion on the shared + * lock in the presence of an exclusive waiter. + */ + if (VOP_ISLOCKED(dp) == LK_EXCLUSIVE) { + crosslkflags &= ~LK_SHARED; + crosslkflags |= LK_EXCLUSIVE | LK_CANRECURSE; + } else if ((crosslkflags & LK_EXCLUSIVE) != 0) { + vn_lock(dp, LK_UPGRADE | LK_RETRY); + if (VN_IS_DOOMED(dp)) { + error = ENOENT; + goto bad2; + } + } else + crosslkflags &= ~LK_NODDLKTREAT; } if (vfs_busy(mp, 0) != 0) continue;
