Messages in this thread | | | Subject | Re: Multi-partition block layer behaviour | From | Shaohua Li <> | Date | Thu, 27 Oct 2011 08:42:41 +0800 |
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On Wed, 2011-10-26 at 18:10 +0800, Tiju Jacob wrote: > >> 1. When an I/O request is made to the filesystem, process 'A' acquires > >> a mutex FS lock and a mutex block driver lock. > >> > >> 2. Process 'B' tries to acquire the mutex FS lock, which is not > >> available. Hence, it goes to sleep. Due to the new plugging mechanism, > >> before going to sleep, shcedule() is invoked which disables preemption > >> and the context becomes atomic. In schedule(), the newly added > >> blk_flush_plug_list() is invoked which unplugs the block driver. > >> > >> 3) During unplug operation the block driver tries to acquire the mutex > >> lock which fails, because the lock was held by process 'A'. Previous > >> invocation of scheudle() in step 2 has already made the context as > >> atomic, hence the error "Schedule while atomic" occured. > > if blk_flush_plug_list() is called in schedule(), it will use > > blk_run_queue_async > > to unplug the queue. This runs in a workqueue. So how could this happen? > > > > The call stack goes as follows: > > From schedule() it calls blk_schedule_flush_plug() and > blk_flush_plug_list() gets invoked. > > In blk_flush_plug_list() queue_unplugged() does not get invoked. Hence > blk_run_queue_async is not called. > Instead __elv_add_request() is invoked with ELEVATOR_INSERT_SORT_MERGE > flag and the flag gets reassigned to ELEVATOR_INSERT_BACK. > > In ELEVATOR_INSERT_BACK, __blk_run_queue() gets invoked and calls request_fn(). This doesn't make sense. why the flag is changed from ELEVATOR_INSERT_SORT_MERGE to ELEVATOR_INSERT_BACK?
can you post a full log? or did your driver have something special?
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