From a8b0026847b8c43445c921ad2c85521c92eb175f Mon Sep 17 00:00:00 2001 From: Al Viro Date: Mon, 20 Nov 2023 20:02:11 -0500 Subject: [PATCH] rename(): avoid a deadlock in the case of parents having no common ancestor ... and fix the directory locking documentation and proof of correctness. Holding ->s_vfs_rename_mutex *almost* prevents ->d_parent changes; the case where we really don't want it is splicing the root of disconnected tree to somewhere. In other words, ->s_vfs_rename_mutex is sufficient to stabilize "X is an ancestor of Y" only if X and Y are already in the same tree. Otherwise it can go from false to true, and one can construct a deadlock on that. Make lock_two_directories() report an error in such case and update the callers of lock_rename()/lock_rename_child() to handle such errors. And yes, such conditions are not impossible to create ;-/ Reviewed-by: Jan Kara Signed-off-by: Al Viro --- .../filesystems/directory-locking.rst | 322 +++++++++++++----- Documentation/filesystems/porting.rst | 9 + fs/cachefiles/namei.c | 2 + fs/ecryptfs/inode.c | 2 + fs/namei.c | 37 +- fs/nfsd/vfs.c | 4 + fs/overlayfs/copy_up.c | 9 +- fs/overlayfs/dir.c | 4 + fs/overlayfs/super.c | 6 +- fs/overlayfs/util.c | 7 +- fs/smb/server/vfs.c | 5 + 11 files changed, 301 insertions(+), 106 deletions(-) diff --git a/Documentation/filesystems/directory-locking.rst b/Documentation/filesystems/directory-locking.rst index 193c22687851..05ea387bc9fb 100644 --- a/Documentation/filesystems/directory-locking.rst +++ b/Documentation/filesystems/directory-locking.rst @@ -11,130 +11,268 @@ When taking the i_rwsem on multiple non-directory objects, we always acquire the locks in order by increasing address. We'll call that "inode pointer" order in the following. -For our purposes all operations fall in 5 classes: -1) read access. Locking rules: caller locks directory we are accessing. -The lock is taken shared. +Primitives +========== -2) object creation. Locking rules: same as above, but the lock is taken -exclusive. +For our purposes all operations fall in 6 classes: -3) object removal. Locking rules: caller locks parent, finds victim, -locks victim and calls the method. Locks are exclusive. +1. read access. Locking rules: -4) rename() that is _not_ cross-directory. Locking rules: caller locks -the parent and finds source and target. Then we decide which of the -source and target need to be locked. Source needs to be locked if it's a -non-directory; target - if it's a non-directory or about to be removed. -Take the locks that need to be taken, in inode pointer order if need -to take both (that can happen only when both source and target are -non-directories - the source because it wouldn't be locked otherwise -and the target because mixing directory and non-directory is allowed -only with RENAME_EXCHANGE, and that won't be removing the target). -After the locks had been taken, call the method. All locks are exclusive. + * lock the directory we are accessing (shared) -5) link creation. Locking rules: +2. object creation. Locking rules: - * lock parent - * check that source is not a directory - * lock source - * call the method. + * lock the directory we are accessing (exclusive) -All locks are exclusive. +3. object removal. Locking rules: -6) cross-directory rename. The trickiest in the whole bunch. Locking -rules: + * lock the parent (exclusive) + * find the victim + * lock the victim (exclusive) + +4. link creation. Locking rules: + + * lock the parent (exclusive) + * check that the source is not a directory + * lock the source (exclusive; probably could be weakened to shared) + +5. rename that is _not_ cross-directory. Locking rules: + + * lock the parent (exclusive) + * find the source and target + * decide which of the source and target need to be locked. + The source needs to be locked if it's a non-directory, target - if it's + a non-directory or about to be removed. + * take the locks that need to be taken (exlusive), in inode pointer order + if need to take both (that can happen only when both source and target + are non-directories - the source because it wouldn't need to be locked + otherwise and the target because mixing directory and non-directory is + allowed only with RENAME_EXCHANGE, and that won't be removing the target). + +6. cross-directory rename. The trickiest in the whole bunch. Locking rules: * lock the filesystem - * lock parents in "ancestors first" order. If one is not ancestor of - the other, lock the parent of source first. - * find source and target. - * if old parent is equal to or is a descendent of target - fail with -ENOTEMPTY - * if new parent is equal to or is a descendent of source - fail with -ELOOP - * Lock subdirectories involved (source before target). - * Lock non-directories involved, in inode pointer order. - * call the method. + * if the parents don't have a common ancestor, fail the operation. + * lock the parents in "ancestors first" order (exclusive). If neither is an + ancestor of the other, lock the parent of source first. + * find the source and target. + * verify that the source is not a descendent of the target and + target is not a descendent of source; fail the operation otherwise. + * lock the subdirectories involved (exclusive), source before target. + * lock the non-directories involved (exclusive), in inode pointer order. -All ->i_rwsem are taken exclusive. +The rules above obviously guarantee that all directories that are going +to be read, modified or removed by method will be locked by the caller. -The rules above obviously guarantee that all directories that are going to be -read, modified or removed by method will be locked by caller. +Splicing +======== + +There is one more thing to consider - splicing. It's not an operation +in its own right; it may happen as part of lookup. We speak of the +operations on directory trees, but we obviously do not have the full +picture of those - especially for network filesystems. What we have +is a bunch of subtrees visible in dcache and locking happens on those. +Trees grow as we do operations; memory pressure prunes them. Normally +that's not a problem, but there is a nasty twist - what should we do +when one growing tree reaches the root of another? That can happen in +several scenarios, starting from "somebody mounted two nested subtrees +from the same NFS4 server and doing lookups in one of them has reached +the root of another"; there's also open-by-fhandle stuff, and there's a +possibility that directory we see in one place gets moved by the server +to another and we run into it when we do a lookup. + +For a lot of reasons we want to have the same directory present in dcache +only once. Multiple aliases are not allowed. So when lookup runs into +a subdirectory that already has an alias, something needs to be done with +dcache trees. Lookup is already holding the parent locked. If alias is +a root of separate tree, it gets attached to the directory we are doing a +lookup in, under the name we'd been looking for. If the alias is already +a child of the directory we are looking in, it changes name to the one +we'd been looking for. No extra locking is involved in these two cases. +However, if it's a child of some other directory, the things get trickier. +First of all, we verify that it is *not* an ancestor of our directory +and fail the lookup if it is. Then we try to lock the filesystem and the +current parent of the alias. If either trylock fails, we fail the lookup. +If trylocks succeed, we detach the alias from its current parent and +attach to our directory, under the name we are looking for. + +Note that splicing does *not* involve any modification of the filesystem; +all we change is the view in dcache. Moreover, holding a directory locked +exclusive prevents such changes involving its children and holding the +filesystem lock prevents any changes of tree topology, other than having a +root of one tree becoming a child of directory in another. In particular, +if two dentries have been found to have a common ancestor after taking +the filesystem lock, their relationship will remain unchanged until +the lock is dropped. So from the directory operations' point of view +splicing is almost irrelevant - the only place where it matters is one +step in cross-directory renames; we need to be careful when checking if +parents have a common ancestor. + + +Multiple-filesystem stuff +========================= + +For some filesystems a method can involve a directory operation on +another filesystem; it may be ecryptfs doing operation in the underlying +filesystem, overlayfs doing something to the layers, network filesystem +using a local one as a cache, etc. In all such cases the operations +on other filesystems must follow the same locking rules. Moreover, "a +directory operation on this filesystem might involve directory operations +on that filesystem" should be an asymmetric relation (or, if you will, +it should be possible to rank the filesystems so that directory operation +on a filesystem could trigger directory operations only on higher-ranked +ones - in these terms overlayfs ranks lower than its layers, network +filesystem ranks lower than whatever it caches on, etc.) + + +Deadlock avoidance +================== If no directory is its own ancestor, the scheme above is deadlock-free. Proof: -[XXX: will be updated once we are done massaging the lock_rename()] - First of all, at any moment we have a linear ordering of the - objects - A < B iff (A is an ancestor of B) or (B is not an ancestor - of A and ptr(A) < ptr(B)). +There is a ranking on the locks, such that all primitives take +them in order of non-decreasing rank. Namely, - That ordering can change. However, the following is true: + * rank ->i_rwsem of non-directories on given filesystem in inode pointer + order. + * put ->i_rwsem of all directories on a filesystem at the same rank, + lower than ->i_rwsem of any non-directory on the same filesystem. + * put ->s_vfs_rename_mutex at rank lower than that of any ->i_rwsem + on the same filesystem. + * among the locks on different filesystems use the relative + rank of those filesystems. -(1) if object removal or non-cross-directory rename holds lock on A and - attempts to acquire lock on B, A will remain the parent of B until we - acquire the lock on B. (Proof: only cross-directory rename can change - the parent of object and it would have to lock the parent). +For example, if we have NFS filesystem caching on a local one, we have -(2) if cross-directory rename holds the lock on filesystem, order will not - change until rename acquires all locks. (Proof: other cross-directory - renames will be blocked on filesystem lock and we don't start changing - the order until we had acquired all locks). + 1. ->s_vfs_rename_mutex of NFS filesystem + 2. ->i_rwsem of directories on that NFS filesystem, same rank for all + 3. ->i_rwsem of non-directories on that filesystem, in order of + increasing address of inode + 4. ->s_vfs_rename_mutex of local filesystem + 5. ->i_rwsem of directories on the local filesystem, same rank for all + 6. ->i_rwsem of non-directories on local filesystem, in order of + increasing address of inode. -(3) locks on non-directory objects are acquired only after locks on - directory objects, and are acquired in inode pointer order. - (Proof: all operations but renames take lock on at most one - non-directory object, except renames, which take locks on source and - target in inode pointer order in the case they are not directories.) +It's easy to verify that operations never take a lock with rank +lower than that of an already held lock. -Now consider the minimal deadlock. Each process is blocked on -attempt to acquire some lock and already holds at least one lock. Let's -consider the set of contended locks. First of all, filesystem lock is -not contended, since any process blocked on it is not holding any locks. -Thus all processes are blocked on ->i_rwsem. +Suppose deadlocks are possible. Consider the minimal deadlocked +set of threads. It is a cycle of several threads, each blocked on a lock +held by the next thread in the cycle. -By (3), any process holding a non-directory lock can only be -waiting on another non-directory lock with a larger address. Therefore -the process holding the "largest" such lock can always make progress, and -non-directory objects are not included in the set of contended locks. +Since the locking order is consistent with the ranking, all +contended locks in the minimal deadlock will be of the same rank, +i.e. they all will be ->i_rwsem of directories on the same filesystem. +Moreover, without loss of generality we can assume that all operations +are done directly to that filesystem and none of them has actually +reached the method call. -Thus link creation can't be a part of deadlock - it can't be -blocked on source and it means that it doesn't hold any locks. +In other words, we have a cycle of threads, T1,..., Tn, +and the same number of directories (D1,...,Dn) such that -Any contended object is either held by cross-directory rename or -has a child that is also contended. Indeed, suppose that it is held by -operation other than cross-directory rename. Then the lock this operation -is blocked on belongs to child of that object due to (1). + T1 is blocked on D1 which is held by T2 -It means that one of the operations is cross-directory rename. -Otherwise the set of contended objects would be infinite - each of them -would have a contended child and we had assumed that no object is its -own descendent. Moreover, there is exactly one cross-directory rename -(see above). + T2 is blocked on D2 which is held by T3 -Consider the object blocking the cross-directory rename. One -of its descendents is locked by cross-directory rename (otherwise we -would again have an infinite set of contended objects). But that -means that cross-directory rename is taking locks out of order. Due -to (2) the order hadn't changed since we had acquired filesystem lock. -But locking rules for cross-directory rename guarantee that we do not -try to acquire lock on descendent before the lock on ancestor. -Contradiction. I.e. deadlock is impossible. Q.E.D. + ... + Tn is blocked on Dn which is held by T1. + +Each operation in the minimal cycle must have locked at least +one directory and blocked on attempt to lock another. That leaves +only 3 possible operations: directory removal (locks parent, then +child), same-directory rename killing a subdirectory (ditto) and +cross-directory rename of some sort. + +There must be a cross-directory rename in the set; indeed, +if all operations had been of the "lock parent, then child" sort +we would have Dn a parent of D1, which is a parent of D2, which is +a parent of D3, ..., which is a parent of Dn. Relationships couldn't +have changed since the moment directory locks had been acquired, +so they would all hold simultaneously at the deadlock time and +we would have a loop. + +Since all operations are on the same filesystem, there can't be +more than one cross-directory rename among them. Without loss of +generality we can assume that T1 is the one doing a cross-directory +rename and everything else is of the "lock parent, then child" sort. + +In other words, we have a cross-directory rename that locked +Dn and blocked on attempt to lock D1, which is a parent of D2, which is +a parent of D3, ..., which is a parent of Dn. Relationships between +D1,...,Dn all hold simultaneously at the deadlock time. Moreover, +cross-directory rename does not get to locking any directories until it +has acquired filesystem lock and verified that directories involved have +a common ancestor, which guarantees that ancestry relationships between +all of them had been stable. + +Consider the order in which directories are locked by the +cross-directory rename; parents first, then possibly their children. +Dn and D1 would have to be among those, with Dn locked before D1. +Which pair could it be? + +It can't be the parents - indeed, since D1 is an ancestor of Dn, +it would be the first parent to be locked. Therefore at least one of the +children must be involved and thus neither of them could be a descendent +of another - otherwise the operation would not have progressed past +locking the parents. + +It can't be a parent and its child; otherwise we would've had +a loop, since the parents are locked before the children, so the parent +would have to be a descendent of its child. + +It can't be a parent and a child of another parent either. +Otherwise the child of the parent in question would've been a descendent +of another child. + +That leaves only one possibility - namely, both Dn and D1 are +among the children, in some order. But that is also impossible, since +neither of the children is a descendent of another. + +That concludes the proof, since the set of operations with the +properties requiered for a minimal deadlock can not exist. + +Note that the check for having a common ancestor in cross-directory +rename is crucial - without it a deadlock would be possible. Indeed, +suppose the parents are initially in different trees; we would lock the +parent of source, then try to lock the parent of target, only to have +an unrelated lookup splice a distant ancestor of source to some distant +descendent of the parent of target. At that point we have cross-directory +rename holding the lock on parent of source and trying to lock its +distant ancestor. Add a bunch of rmdir() attempts on all directories +in between (all of those would fail with -ENOTEMPTY, had they ever gotten +the locks) and voila - we have a deadlock. + +Loop avoidance +============== These operations are guaranteed to avoid loop creation. Indeed, the only operation that could introduce loops is cross-directory rename. -Since the only new (parent, child) pair added by rename() is (new parent, -source), such loop would have to contain these objects and the rest of it -would have to exist before rename(). I.e. at the moment of loop creation -rename() responsible for that would be holding filesystem lock and new parent -would have to be equal to or a descendent of source. But that means that -new parent had been equal to or a descendent of source since the moment when -we had acquired filesystem lock and rename() would fail with -ELOOP in that -case. +Suppose after the operation there is a loop; since there hadn't been such +loops before the operation, at least on of the nodes in that loop must've +had its parent changed. In other words, the loop must be passing through +the source or, in case of exchange, possibly the target. + +Since the operation has succeeded, neither source nor target could have +been ancestors of each other. Therefore the chain of ancestors starting +in the parent of source could not have passed through the target and +vice versa. On the other hand, the chain of ancestors of any node could +not have passed through the node itself, or we would've had a loop before +the operation. But everything other than source and target has kept +the parent after the operation, so the operation does not change the +chains of ancestors of (ex-)parents of source and target. In particular, +those chains must end after a finite number of steps. + +Now consider the loop created by the operation. It passes through either +source or target; the next node in the loop would be the ex-parent of +target or source resp. After that the loop would follow the chain of +ancestors of that parent. But as we have just shown, that chain must +end after a finite number of steps, which means that it can't be a part +of any loop. Q.E.D. While this locking scheme works for arbitrary DAGs, it relies on ability to check that directory is a descendent of another object. Current diff --git a/Documentation/filesystems/porting.rst b/Documentation/filesystems/porting.rst index 9100969e7de6..33cd56e2ca1a 100644 --- a/Documentation/filesystems/porting.rst +++ b/Documentation/filesystems/porting.rst @@ -1079,3 +1079,12 @@ On same-directory ->rename() the (tautological) update of .. is not protected by any locks; just don't do it if the old parent is the same as the new one. We really can't lock two subdirectories in same-directory rename - not without deadlocks. + +--- + +**mandatory** + +lock_rename() and lock_rename_child() may fail in cross-directory case, if +their arguments do not have a common ancestor. In that case ERR_PTR(-EXDEV) +is returned, with no locks taken. In-tree users updated; out-of-tree ones +would need to do so. diff --git a/fs/cachefiles/namei.c b/fs/cachefiles/namei.c index 7bf7a5fcc045..7ade836beb58 100644 --- a/fs/cachefiles/namei.c +++ b/fs/cachefiles/namei.c @@ -305,6 +305,8 @@ try_again: /* do the multiway lock magic */ trap = lock_rename(cache->graveyard, dir); + if (IS_ERR(trap)) + return PTR_ERR(trap); /* do some checks before getting the grave dentry */ if (rep->d_parent != dir || IS_DEADDIR(d_inode(rep))) { diff --git a/fs/ecryptfs/inode.c b/fs/ecryptfs/inode.c index a25dd3d20008..8efd20dc902b 100644 --- a/fs/ecryptfs/inode.c +++ b/fs/ecryptfs/inode.c @@ -599,6 +599,8 @@ ecryptfs_rename(struct mnt_idmap *idmap, struct inode *old_dir, target_inode = d_inode(new_dentry); trap = lock_rename(lower_old_dir_dentry, lower_new_dir_dentry); + if (IS_ERR(trap)) + return PTR_ERR(trap); dget(lower_new_dentry); rc = -EINVAL; if (lower_old_dentry->d_parent != lower_old_dir_dentry) diff --git a/fs/namei.c b/fs/namei.c index 29bafbdb44ca..6b0302ac80d1 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -3014,21 +3014,37 @@ static inline int may_create(struct mnt_idmap *idmap, return inode_permission(idmap, dir, MAY_WRITE | MAY_EXEC); } +// p1 != p2, both are on the same filesystem, ->s_vfs_rename_mutex is held static struct dentry *lock_two_directories(struct dentry *p1, struct dentry *p2) { - struct dentry *p; + struct dentry *p = p1, *q = p2, *r; - p = d_ancestor(p2, p1); - if (p) { + while ((r = p->d_parent) != p2 && r != p) + p = r; + if (r == p2) { + // p is a child of p2 and an ancestor of p1 or p1 itself inode_lock_nested(p2->d_inode, I_MUTEX_PARENT); inode_lock_nested(p1->d_inode, I_MUTEX_PARENT2); return p; } - - p = d_ancestor(p1, p2); - inode_lock_nested(p1->d_inode, I_MUTEX_PARENT); - inode_lock_nested(p2->d_inode, I_MUTEX_PARENT2); - return p; + // p is the root of connected component that contains p1 + // p2 does not occur on the path from p to p1 + while ((r = q->d_parent) != p1 && r != p && r != q) + q = r; + if (r == p1) { + // q is a child of p1 and an ancestor of p2 or p2 itself + inode_lock_nested(p1->d_inode, I_MUTEX_PARENT); + inode_lock_nested(p2->d_inode, I_MUTEX_PARENT2); + return q; + } else if (likely(r == p)) { + // both p2 and p1 are descendents of p + inode_lock_nested(p1->d_inode, I_MUTEX_PARENT); + inode_lock_nested(p2->d_inode, I_MUTEX_PARENT2); + return NULL; + } else { // no common ancestor at the time we'd been called + mutex_unlock(&p1->d_sb->s_vfs_rename_mutex); + return ERR_PTR(-EXDEV); + } } /* @@ -4947,6 +4963,10 @@ retry: retry_deleg: trap = lock_rename(new_path.dentry, old_path.dentry); + if (IS_ERR(trap)) { + error = PTR_ERR(trap); + goto exit_lock_rename; + } old_dentry = lookup_one_qstr_excl(&old_last, old_path.dentry, lookup_flags); @@ -5014,6 +5034,7 @@ exit4: dput(old_dentry); exit3: unlock_rename(new_path.dentry, old_path.dentry); +exit_lock_rename: if (delegated_inode) { error = break_deleg_wait(&delegated_inode); if (!error) diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c index fbbea7498f02..a99260c3f9bc 100644 --- a/fs/nfsd/vfs.c +++ b/fs/nfsd/vfs.c @@ -1813,6 +1813,10 @@ retry: } trap = lock_rename(tdentry, fdentry); + if (IS_ERR(trap)) { + err = (rqstp->rq_vers == 2) ? nfserr_acces : nfserr_xdev; + goto out; + } err = fh_fill_pre_attrs(ffhp); if (err != nfs_ok) goto out_unlock; diff --git a/fs/overlayfs/copy_up.c b/fs/overlayfs/copy_up.c index 4382881b0709..e44dc5f66161 100644 --- a/fs/overlayfs/copy_up.c +++ b/fs/overlayfs/copy_up.c @@ -722,7 +722,7 @@ static int ovl_copy_up_workdir(struct ovl_copy_up_ctx *c) struct inode *inode; struct inode *udir = d_inode(c->destdir), *wdir = d_inode(c->workdir); struct path path = { .mnt = ovl_upper_mnt(ofs) }; - struct dentry *temp, *upper; + struct dentry *temp, *upper, *trap; struct ovl_cu_creds cc; int err; struct ovl_cattr cattr = { @@ -760,9 +760,11 @@ static int ovl_copy_up_workdir(struct ovl_copy_up_ctx *c) * If temp was moved, abort without the cleanup. */ ovl_start_write(c->dentry); - if (lock_rename(c->workdir, c->destdir) != NULL || - temp->d_parent != c->workdir) { + trap = lock_rename(c->workdir, c->destdir); + if (trap || temp->d_parent != c->workdir) { err = -EIO; + if (IS_ERR(trap)) + goto out; goto unlock; } else if (err) { goto cleanup; @@ -803,6 +805,7 @@ static int ovl_copy_up_workdir(struct ovl_copy_up_ctx *c) ovl_set_flag(OVL_WHITEOUTS, inode); unlock: unlock_rename(c->workdir, c->destdir); +out: ovl_end_write(c->dentry); return err; diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c index aab3f5d93556..0f8b4a719237 100644 --- a/fs/overlayfs/dir.c +++ b/fs/overlayfs/dir.c @@ -1180,6 +1180,10 @@ static int ovl_rename(struct mnt_idmap *idmap, struct inode *olddir, } trap = lock_rename(new_upperdir, old_upperdir); + if (IS_ERR(trap)) { + err = PTR_ERR(trap); + goto out_revert_creds; + } olddentry = ovl_lookup_upper(ofs, old->d_name.name, old_upperdir, old->d_name.len); diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c index a0967bb25003..fc3a6ff648bd 100644 --- a/fs/overlayfs/super.c +++ b/fs/overlayfs/super.c @@ -439,8 +439,10 @@ static bool ovl_workdir_ok(struct dentry *workdir, struct dentry *upperdir) bool ok = false; if (workdir != upperdir) { - ok = (lock_rename(workdir, upperdir) == NULL); - unlock_rename(workdir, upperdir); + struct dentry *trap = lock_rename(workdir, upperdir); + if (!IS_ERR(trap)) + unlock_rename(workdir, upperdir); + ok = (trap == NULL); } return ok; } diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c index 50a201e9cd39..7b667345e673 100644 --- a/fs/overlayfs/util.c +++ b/fs/overlayfs/util.c @@ -1198,12 +1198,17 @@ void ovl_nlink_end(struct dentry *dentry) int ovl_lock_rename_workdir(struct dentry *workdir, struct dentry *upperdir) { + struct dentry *trap; + /* Workdir should not be the same as upperdir */ if (workdir == upperdir) goto err; /* Workdir should not be subdir of upperdir and vice versa */ - if (lock_rename(workdir, upperdir) != NULL) + trap = lock_rename(workdir, upperdir); + if (IS_ERR(trap)) + goto err; + if (trap) goto err_unlock; return 0; diff --git a/fs/smb/server/vfs.c b/fs/smb/server/vfs.c index c53dea5598fc..4cf8523ad038 100644 --- a/fs/smb/server/vfs.c +++ b/fs/smb/server/vfs.c @@ -708,6 +708,10 @@ retry: goto out2; trap = lock_rename_child(old_child, new_path.dentry); + if (IS_ERR(trap)) { + err = PTR_ERR(trap); + goto out_drop_write; + } old_parent = dget(old_child->d_parent); if (d_unhashed(old_child)) { @@ -770,6 +774,7 @@ out4: out3: dput(old_parent); unlock_rename(old_parent, new_path.dentry); +out_drop_write: mnt_drop_write(old_path->mnt); out2: path_put(&new_path);