4.11-stable review patch. If anyone has any objections, please let me know. ------------------ From: Rabin Vincent <rabinv@xxxxxxxx> commit 3998e6b87d4258a70df358296d6f1c7234012bfe upstream. When the final cifsFileInfo_put() is called from cifsiod and an oplock break work is queued, lockdep complains loudly: ============================================= [ INFO: possible recursive locking detected ] 4.11.0+ #21 Not tainted --------------------------------------------- kworker/0:2/78 is trying to acquire lock: ("cifsiod"){++++.+}, at: flush_work+0x215/0x350 but task is already holding lock: ("cifsiod"){++++.+}, at: process_one_work+0x255/0x8e0 other info that might help us debug this: Possible unsafe locking scenario: CPU0 ---- lock("cifsiod"); lock("cifsiod"); *** DEADLOCK *** May be due to missing lock nesting notation 2 locks held by kworker/0:2/78: #0: ("cifsiod"){++++.+}, at: process_one_work+0x255/0x8e0 #1: ((&wdata->work)){+.+...}, at: process_one_work+0x255/0x8e0 stack backtrace: CPU: 0 PID: 78 Comm: kworker/0:2 Not tainted 4.11.0+ #21 Workqueue: cifsiod cifs_writev_complete Call Trace: dump_stack+0x85/0xc2 __lock_acquire+0x17dd/0x2260 ? match_held_lock+0x20/0x2b0 ? trace_hardirqs_off_caller+0x86/0x130 ? mark_lock+0xa6/0x920 lock_acquire+0xcc/0x260 ? lock_acquire+0xcc/0x260 ? flush_work+0x215/0x350 flush_work+0x236/0x350 ? flush_work+0x215/0x350 ? destroy_worker+0x170/0x170 __cancel_work_timer+0x17d/0x210 ? ___preempt_schedule+0x16/0x18 cancel_work_sync+0x10/0x20 cifsFileInfo_put+0x338/0x7f0 cifs_writedata_release+0x2a/0x40 ? cifs_writedata_release+0x2a/0x40 cifs_writev_complete+0x29d/0x850 ? preempt_count_sub+0x18/0xd0 process_one_work+0x304/0x8e0 worker_thread+0x9b/0x6a0 kthread+0x1b2/0x200 ? process_one_work+0x8e0/0x8e0 ? kthread_create_on_node+0x40/0x40 ret_from_fork+0x31/0x40 This is a real warning. Since the oplock is queued on the same workqueue this can deadlock if there is only one worker thread active for the workqueue (which will be the case during memory pressure when the rescuer thread is handling it). Furthermore, there is at least one other kind of hang possible due to the oplock break handling if there is only worker. (This can be reproduced without introducing memory pressure by having passing 1 for the max_active parameter of cifsiod.) cifs_oplock_break() can wait indefintely in the filemap_fdatawait() while the cifs_writev_complete() work is blocked: sysrq: SysRq : Show Blocked State task PC stack pid father kworker/0:1 D 0 16 2 0x00000000 Workqueue: cifsiod cifs_oplock_break Call Trace: __schedule+0x562/0xf40 ? mark_held_locks+0x4a/0xb0 schedule+0x57/0xe0 io_schedule+0x21/0x50 wait_on_page_bit+0x143/0x190 ? add_to_page_cache_lru+0x150/0x150 __filemap_fdatawait_range+0x134/0x190 ? do_writepages+0x51/0x70 filemap_fdatawait_range+0x14/0x30 filemap_fdatawait+0x3b/0x40 cifs_oplock_break+0x651/0x710 ? preempt_count_sub+0x18/0xd0 process_one_work+0x304/0x8e0 worker_thread+0x9b/0x6a0 kthread+0x1b2/0x200 ? process_one_work+0x8e0/0x8e0 ? kthread_create_on_node+0x40/0x40 ret_from_fork+0x31/0x40 dd D 0 683 171 0x00000000 Call Trace: __schedule+0x562/0xf40 ? mark_held_locks+0x29/0xb0 schedule+0x57/0xe0 io_schedule+0x21/0x50 wait_on_page_bit+0x143/0x190 ? add_to_page_cache_lru+0x150/0x150 __filemap_fdatawait_range+0x134/0x190 ? do_writepages+0x51/0x70 filemap_fdatawait_range+0x14/0x30 filemap_fdatawait+0x3b/0x40 filemap_write_and_wait+0x4e/0x70 cifs_flush+0x6a/0xb0 filp_close+0x52/0xa0 __close_fd+0xdc/0x150 SyS_close+0x33/0x60 entry_SYSCALL_64_fastpath+0x1f/0xbe Showing all locks held in the system: 2 locks held by kworker/0:1/16: #0: ("cifsiod"){.+.+.+}, at: process_one_work+0x255/0x8e0 #1: ((&cfile->oplock_break)){+.+.+.}, at: process_one_work+0x255/0x8e0 Showing busy workqueues and worker pools: workqueue cifsiod: flags=0xc pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=1/1 in-flight: 16:cifs_oplock_break delayed: cifs_writev_complete, cifs_echo_request pool 0: cpus=0 node=0 flags=0x0 nice=0 hung=0s workers=3 idle: 750 3 Fix these problems by creating a a new workqueue (with a rescuer) for the oplock break work. Signed-off-by: Rabin Vincent <rabinv@xxxxxxxx> Signed-off-by: Steve French <smfrench@xxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- fs/cifs/cifsfs.c | 15 +++++++++++++-- fs/cifs/cifsglob.h | 1 + fs/cifs/misc.c | 2 +- fs/cifs/smb2misc.c | 5 +++-- 4 files changed, 18 insertions(+), 5 deletions(-) --- a/fs/cifs/cifsfs.c +++ b/fs/cifs/cifsfs.c @@ -87,6 +87,7 @@ extern mempool_t *cifs_req_poolp; extern mempool_t *cifs_mid_poolp; struct workqueue_struct *cifsiod_wq; +struct workqueue_struct *cifsoplockd_wq; __u32 cifs_lock_secret; /* @@ -1369,9 +1370,16 @@ init_cifs(void) goto out_clean_proc; } + cifsoplockd_wq = alloc_workqueue("cifsoplockd", + WQ_FREEZABLE|WQ_MEM_RECLAIM, 0); + if (!cifsoplockd_wq) { + rc = -ENOMEM; + goto out_destroy_cifsiod_wq; + } + rc = cifs_fscache_register(); if (rc) - goto out_destroy_wq; + goto out_destroy_cifsoplockd_wq; rc = cifs_init_inodecache(); if (rc) @@ -1419,7 +1427,9 @@ out_destroy_inodecache: cifs_destroy_inodecache(); out_unreg_fscache: cifs_fscache_unregister(); -out_destroy_wq: +out_destroy_cifsoplockd_wq: + destroy_workqueue(cifsoplockd_wq); +out_destroy_cifsiod_wq: destroy_workqueue(cifsiod_wq); out_clean_proc: cifs_proc_clean(); @@ -1442,6 +1452,7 @@ exit_cifs(void) cifs_destroy_mids(); cifs_destroy_inodecache(); cifs_fscache_unregister(); + destroy_workqueue(cifsoplockd_wq); destroy_workqueue(cifsiod_wq); cifs_proc_clean(); } --- a/fs/cifs/cifsglob.h +++ b/fs/cifs/cifsglob.h @@ -1683,6 +1683,7 @@ void cifs_oplock_break(struct work_struc extern const struct slow_work_ops cifs_oplock_break_ops; extern struct workqueue_struct *cifsiod_wq; +extern struct workqueue_struct *cifsoplockd_wq; extern __u32 cifs_lock_secret; extern mempool_t *cifs_mid_poolp; --- a/fs/cifs/misc.c +++ b/fs/cifs/misc.c @@ -492,7 +492,7 @@ is_valid_oplock_break(char *buffer, stru CIFS_INODE_DOWNGRADE_OPLOCK_TO_L2, &pCifsInode->flags); - queue_work(cifsiod_wq, + queue_work(cifsoplockd_wq, &netfile->oplock_break); netfile->oplock_break_cancelled = false; --- a/fs/cifs/smb2misc.c +++ b/fs/cifs/smb2misc.c @@ -499,7 +499,7 @@ smb2_tcon_has_lease(struct cifs_tcon *tc else cfile->oplock_break_cancelled = true; - queue_work(cifsiod_wq, &cfile->oplock_break); + queue_work(cifsoplockd_wq, &cfile->oplock_break); kfree(lw); return true; } @@ -643,7 +643,8 @@ smb2_is_valid_oplock_break(char *buffer, CIFS_INODE_DOWNGRADE_OPLOCK_TO_L2, &cinode->flags); spin_unlock(&cfile->file_info_lock); - queue_work(cifsiod_wq, &cfile->oplock_break); + queue_work(cifsoplockd_wq, + &cfile->oplock_break); spin_unlock(&tcon->open_file_lock); spin_unlock(&cifs_tcp_ses_lock);