From a30efe261b5a8fb2e3cf8ea9c3aca51e0619c2cc Mon Sep 17 00:00:00 2001 From: David Howells Date: Tue, 30 Sep 2014 14:50:30 +0100 Subject: [PATCH] CacheFiles: Fix incorrect test for in-memory object collision MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit When CacheFiles cache objects are in use, they have in-memory representations, as defined by the cachefiles_object struct. These are kept in a tree rooted in the cache and indexed by dentry pointer (since there's a unique mapping between object index key and dentry). Collisions can occur between a representation already in the tree and a new representation being set up because it takes time to dispose of an old representation - particularly if it must be unlinked or renamed. When such a collision occurs, cachefiles_mark_object_active() is meant to check to see if the old, already-present representation is in the process of being discarded (ie. FSCACHE_OBJECT_IS_LIVE is not set on it) - and, if so, wait for the representation to be removed (ie. CACHEFILES_OBJECT_ACTIVE is then cleared). However, the test for whether the old representation is still live is checking the new object - which always will be live at this point. This leads to an oops looking like: CacheFiles: Error: Unexpected object collision object: OBJ1b354 objstate=LOOK_UP_OBJECT fl=8 wbusy=2 ev=0[0] ops=0 inp=0 exc=0 parent=ffff88053f5417c0 cookie=ffff880538f202a0 [pr=ffff8805381b7160 nd=ffff880509c6eb78 fl=27] key=[8] '2490000000000000' xobject: OBJ1a600 xobjstate=DROP_OBJECT fl=70 wbusy=2 ev=0[0] xops=0 inp=0 exc=0 xparent=ffff88053f5417c0 xcookie=ffff88050f4cbf70 [pr=ffff8805381b7160 nd= (null) fl=12] ------------[ cut here ]------------ kernel BUG at fs/cachefiles/namei.c:200! ... Workqueue: fscache_object fscache_object_work_func [fscache] ... RIP: ... cachefiles_walk_to_object+0x7ea/0x860 [cachefiles] ... Call Trace: [] ? cachefiles_lookup_object+0x58/0x100 [cachefiles] [] ? fscache_look_up_object+0xb9/0x1d0 [fscache] [] ? fscache_parent_ready+0x2d/0x80 [fscache] [] ? fscache_object_work_func+0x92/0x1f0 [fscache] [] ? process_one_work+0x16b/0x400 [] ? worker_thread+0x116/0x380 [] ? manage_workers.isra.21+0x290/0x290 [] ? kthread+0xbc/0xe0 [] ? flush_kthread_worker+0x80/0x80 [] ? ret_from_fork+0x7c/0xb0 [] ? flush_kthread_worker+0x80/0x80 Reported-by: Manuel Schölling Signed-off-by: David Howells Acked-by: Steve Dickson --- fs/cachefiles/namei.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/fs/cachefiles/namei.c b/fs/cachefiles/namei.c index dad7d9542a24..e12f189d539b 100644 --- a/fs/cachefiles/namei.c +++ b/fs/cachefiles/namei.c @@ -189,7 +189,7 @@ try_again: /* an old object from a previous incarnation is hogging the slot - we * need to wait for it to be destroyed */ wait_for_old_object: - if (fscache_object_is_live(&object->fscache)) { + if (fscache_object_is_live(&xobject->fscache)) { pr_err("\n"); pr_err("Error: Unexpected object collision\n"); cachefiles_printk_object(object, xobject); -- 2.20.1