diff options
| -rw-r--r-- | fs/locks.c | 75 | ||||
| -rw-r--r-- | include/linux/fs.h | 6 |
2 files changed, 68 insertions, 13 deletions
diff --git a/fs/locks.c b/fs/locks.c index 92a0f0a52b06..2cfeea622f28 100644 --- a/fs/locks.c +++ b/fs/locks.c @@ -652,15 +652,18 @@ static void locks_insert_lock(struct file_lock **pos, struct file_lock *fl) locks_insert_global_locks(fl); } -/* - * Delete a lock and then free it. - * Wake up processes that are blocked waiting for this lock, - * notify the FS that the lock has been cleared and - * finally free the lock. +/** + * locks_delete_lock - Delete a lock and then free it. + * @thisfl_p: pointer that points to the fl_next field of the previous + * inode->i_flock list entry + * + * Unlink a lock from all lists and free the namespace reference, but don't + * free it yet. Wake up processes that are blocked waiting for this lock and + * notify the FS that the lock has been cleared. * * Must be called with the i_lock held! */ -static void locks_delete_lock(struct file_lock **thisfl_p) +static void locks_unlink_lock(struct file_lock **thisfl_p) { struct file_lock *fl = *thisfl_p; @@ -675,6 +678,18 @@ static void locks_delete_lock(struct file_lock **thisfl_p) } locks_wake_up_blocks(fl); +} + +/* + * Unlink a lock from all lists and free it. + * + * Must be called with i_lock held! + */ +static void locks_delete_lock(struct file_lock **thisfl_p) +{ + struct file_lock *fl = *thisfl_p; + + locks_unlink_lock(thisfl_p); locks_free_lock(fl); } @@ -1472,6 +1487,32 @@ int fcntl_getlease(struct file *filp) return type; } +/** + * check_conflicting_open - see if the given dentry points to a file that has + * an existing open that would conflict with the + * desired lease. + * @dentry: dentry to check + * @arg: type of lease that we're trying to acquire + * + * Check to see if there's an existing open fd on this file that would + * conflict with the lease we're trying to set. + */ +static int +check_conflicting_open(const struct dentry *dentry, const long arg) +{ + int ret = 0; + struct inode *inode = dentry->d_inode; + + if ((arg == F_RDLCK) && (atomic_read(&inode->i_writecount) > 0)) + return -EAGAIN; + + if ((arg == F_WRLCK) && ((d_count(dentry) > 1) || + (atomic_read(&inode->i_count) > 1))) + ret = -EAGAIN; + + return ret; +} + static int generic_add_lease(struct file *filp, long arg, struct file_lock **flp) { struct file_lock *fl, **before, **my_before = NULL, *lease; @@ -1499,12 +1540,8 @@ static int generic_add_lease(struct file *filp, long arg, struct file_lock **flp return -EINVAL; } - error = -EAGAIN; - if ((arg == F_RDLCK) && (atomic_read(&inode->i_writecount) > 0)) - goto out; - if ((arg == F_WRLCK) - && ((d_count(dentry) > 1) - || (atomic_read(&inode->i_count) > 1))) + error = check_conflicting_open(dentry, arg); + if (error) goto out; /* @@ -1549,7 +1586,19 @@ static int generic_add_lease(struct file *filp, long arg, struct file_lock **flp goto out; locks_insert_lock(before, lease); - error = 0; + /* + * The check in break_lease() is lockless. It's possible for another + * open to race in after we did the earlier check for a conflicting + * open but before the lease was inserted. Check again for a + * conflicting open and cancel the lease if there is one. + * + * We also add a barrier here to ensure that the insertion of the lock + * precedes these checks. + */ + smp_mb(); + error = check_conflicting_open(dentry, arg); + if (error) + locks_unlink_lock(flp); out: if (is_deleg) mutex_unlock(&inode->i_mutex); diff --git a/include/linux/fs.h b/include/linux/fs.h index 09f553c59813..df8474408331 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -1964,6 +1964,12 @@ static inline int locks_verify_truncate(struct inode *inode, static inline int break_lease(struct inode *inode, unsigned int mode) { + /* + * Since this check is lockless, we must ensure that any refcounts + * taken are done before checking inode->i_flock. Otherwise, we could + * end up racing with tasks trying to set a new lease on this file. + */ + smp_mb(); if (inode->i_flock) return __break_lease(inode, mode, FL_LEASE); return 0; |