Date: Fri, 13 Oct 2023 23:53:49 GMT From: Mateusz Guzik <mjg@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-branches@FreeBSD.org Subject: git: c3dc958cacd8 - stable/13 - vfs cache: plug a hypothetical corner case when freeing Message-ID: <202310132353.39DNrnt9032001@gitrepo.freebsd.org>
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The branch stable/13 has been updated by mjg: URL: https://cgit.FreeBSD.org/src/commit/?id=c3dc958cacd819c9fe989477371f01c187873cc0 commit c3dc958cacd819c9fe989477371f01c187873cc0 Author: Mateusz Guzik <mjg@FreeBSD.org> AuthorDate: 2023-09-23 02:04:06 +0000 Commit: Mateusz Guzik <mjg@FreeBSD.org> CommitDate: 2023-10-13 23:48:12 +0000 vfs cache: plug a hypothetical corner case when freeing cache_zap_unlocked_bucket is called with a bunch of addresses and without any locks held, forcing it to revalidate everything from scratch. It did not account for a case where the entry is reallocated with everything the same except for the target vnode. Should the target use a different lock than the one expected, freeing would proceed without being properly synchronized. Note this is almost impossible to happen in practice. (cherry picked from commit 0f15054f7990f9c772bea34778a8838aa05ebed8) --- sys/kern/vfs_cache.c | 25 ++++++++++++++++++------- 1 file changed, 18 insertions(+), 7 deletions(-) diff --git a/sys/kern/vfs_cache.c b/sys/kern/vfs_cache.c index 1d52b2e63169..49e66803a1d1 100644 --- a/sys/kern/vfs_cache.c +++ b/sys/kern/vfs_cache.c @@ -1649,6 +1649,7 @@ cache_zap_unlocked_bucket(struct namecache *ncp, struct componentname *cnp, struct mtx *blp) { struct namecache *rncp; + struct mtx *rvlp; cache_assert_bucket_unlocked(ncp); @@ -1661,14 +1662,24 @@ cache_zap_unlocked_bucket(struct namecache *ncp, struct componentname *cnp, !bcmp(rncp->nc_name, cnp->cn_nameptr, rncp->nc_nlen)) break; } - if (rncp != NULL) { - cache_zap_locked(rncp); - mtx_unlock(blp); - cache_unlock_vnodes(dvlp, vlp); - atomic_add_long(&zap_bucket_relock_success, 1); - return (0); - } + if (rncp == NULL) + goto out_mismatch; + + if (!(ncp->nc_flag & NCF_NEGATIVE)) + rvlp = VP2VNODELOCK(rncp->nc_vp); + else + rvlp = NULL; + if (rvlp != vlp) + goto out_mismatch; + + cache_zap_locked(rncp); + mtx_unlock(blp); + cache_unlock_vnodes(dvlp, vlp); + atomic_add_long(&zap_bucket_relock_success, 1); + return (0); + +out_mismatch: mtx_unlock(blp); cache_unlock_vnodes(dvlp, vlp); return (EAGAIN);
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