On 6/1/21 3:25 PM, Ming Lei wrote: > On Tue, Jun 01, 2021 at 01:01:45PM +0200, Hannes Reinecke wrote: >> __disk_unblock_events() will call queue_delayed_work() with a '0' argument >> under a spin lock. This might cause the queue_work item to be executed >> immediately, and run into a deadlock in disk_check_events() waiting for >> the lock to be released. > > Do you have lockdep warning on this 'deadlock'? > > Executed immediately doesn't mean the work fn is run in the current > task context, and it is actually run in one wq worker(task) context, so > __queue_work() usually wakes up one wq worker for running the work fn, > then there shouldn't be the 'deadlock' you mentioned. > That's what I thought, too, but then we have a customer report complaining about a stuck installation, and this kernel message: > [ 990.305908] INFO: task init:1 blocked for more than 491 seconds. > [ 990.311904] Not tainted 5.3.18-22-default #1 > [ 990.316682] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. > [ 990.324483] init D 0 1 0 0x00000000 > [ 990.329950] Call Trace: > [ 990.332396] __schedule+0x28a/0x6d0 > [ 990.335876] ? work_busy+0x80/0x80 > [ 990.339267] schedule+0x2f/0xa0 > [ 990.342399] schedule_timeout+0x1dd/0x300 > [ 990.346399] ? check_preempt_curr+0x29/0x80 > [ 990.350569] ? ttwu_do_wakeup+0x19/0x150 > [ 990.354480] ? work_busy+0x80/0x80 > [ 990.357869] wait_for_completion+0xba/0x140 > [ 990.362040] ? wake_up_q+0xa0/0xa0 > [ 990.365430] __flush_work+0x177/0x1d0 > [ 990.369080] ? worker_detach_from_pool+0xa0/0xa0 > [ 990.373682] __cancel_work_timer+0x12b/0x1b0 > [ 990.377940] ? exact_lock+0xd/0x20 > [ 990.381329] ? kobj_lookup+0x113/0x160 > [ 990.385067] disk_block_events+0x78/0x90 > [ 990.388979] __blkdev_get+0x6d/0x7e0 > [ 990.392542] ? blkdev_get_by_dev+0x40/0x40 > [ 990.396627] do_dentry_open+0x1ea/0x380 > [ 990.400450] path_openat+0x2fc/0x1520 > [ 990.404103] do_filp_open+0x9b/0x110 > [ 990.407667] ? kmem_cache_alloc+0x3d/0x250 > [ 990.411749] ? do_sys_open+0x1bd/0x250 > [ 990.415486] do_sys_open+0x1bd/0x250 > [ 990.419052] do_syscall_64+0x5b/0x1e0 > [ 990.422701] entry_SYSCALL_64_after_hwframe+0x44/0xa9 Which does vanish with this patch. Cheers, Hannes -- Dr. Hannes Reinecke Kernel Storage Architect hare@xxxxxxx +49 911 74053 688 SUSE Software Solutions Germany GmbH, 90409 Nürnberg GF: F. Imendörffer, HRB 36809 (AG Nürnberg)
