From: KiranKumar Modukuri <[email protected]> In cachefiles_mark_object_active(), the new object is marked active and then we try to add it to the active object tree. If a conflicting object is already present, we want to wait for that to go away. After the wait, we go round again and try to re-mark the object as being active - but it's already marked active from the first time we went through and a BUG is issued.
Fix this by clearing the CACHEFILES_OBJECT_ACTIVE flag before we try again. Analysis from Kiran Kumar Modukuri: [Impact] Oops during heavy NFS + FSCache + Cachefiles CacheFiles: Error: Overlong wait for old active object to go away. BUG: unable to handle kernel NULL pointer dereference at 0000000000000002 CacheFiles: Error: Object already active kernel BUG at fs/cachefiles/namei.c:163! [Cause] In a heavily loaded system with big files being read and truncated, an fscache object for a cookie is being dropped and a new object being looked. The new object being looked for has to wait for the old object to go away before the new object is moved to active state. [Fix] Clear the flag 'CACHEFILES_OBJECT_ACTIVE' for the new object when retrying the object lookup. [Testcase] Have run ~100 hours of NFS stress tests and have not seen this bug recur. [Regression Potential] - Limited to fscache/cachefiles. Signed-off-by: Kiran Kumar Modukuri <[email protected]> Signed-off-by: David Howells <[email protected]> --- 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 ab0bbe93b398..b5d6dd72dfa0 100644 --- a/fs/cachefiles/namei.c +++ b/fs/cachefiles/namei.c @@ -186,6 +186,7 @@ static int cachefiles_mark_object_active(struct cachefiles_cache *cache, * need to wait for it to be destroyed */ wait_for_old_object: trace_cachefiles_wait_active(object, dentry, xobject); + clear_bit(CACHEFILES_OBJECT_ACTIVE, &object->flags); if (fscache_object_is_live(&xobject->fscache)) { pr_err("\n"); @@ -248,7 +249,6 @@ static int cachefiles_mark_object_active(struct cachefiles_cache *cache, goto try_again; requeue: - clear_bit(CACHEFILES_OBJECT_ACTIVE, &object->flags); cache->cache.ops->put_object(&xobject->fscache, cachefiles_obj_put_wait_timeo); _leave(" = -ETIMEDOUT"); return -ETIMEDOUT; -- Linux-cachefs mailing list [email protected] https://www.redhat.com/mailman/listinfo/linux-cachefs
