On Tue, Oct 13, 2020 at 04:17:02PM +0530, Pratham Pratap wrote: > Consider a case where host is trying to submit urbs to the > connected device while holding the us->dev_mutex and due to > some reason it is stuck while waiting for the completion of > the urbs. Now the scsi error mechanism kicks in and it calls > the device reset handler which is trying to acquire the same > mutex causing a deadlock situation. > > Below is the call stack of the task which acquired the mutex > (0xFFFFFFC660447460) and waiting for completion. > > B::v.f_/task_0xFFFFFFC6604DB280 > -000|__switch_to(prev = 0xFFFFFFC6604DB280, ?) > -001|prepare_lock_switch(inline) > -001|context_switch(inline) > -001|__schedule(?) > -002|schedule() > -003|schedule_timeout(timeout = 9223372036854775807) > -004|do_wait_for_common(x = 0xFFFFFFC660447570, > action = 0xFFFFFF98ED5A7398, timeout = 9223372036854775807, ?) > -005|spin_unlock_irq(inline) > -005|__wait_for_common(inline) > -005|wait_for_common(inline) > -005|wait_for_completion(x = 0xFFFFFFC660447570) > -006|sg_clean(inline) > -006|usb_sg_wait() > -007|atomic64_andnot(inline) > -007|atomic_long_andnot(inline) > -007|clear_bit(inline) > -007|usb_stor_bulk_transfer_sglist(us = 0xFFFFFFC660447460, > pipe = 3221291648, sg = 0xFFFFFFC65D6415D0, ?, length = 512, > act_len = 0xFFFFFF801258BC90)
No need to line-wrap for stuff like this. > -008|scsi_bufflen(inline) > -008|usb_stor_bulk_srb(inline) > -008|usb_stor_Bulk_transport(srb = 0xFFFFFFC65D641438, > us = 0xFFFFFFC660447460) > -009|test_bit(inline) > -009|usb_stor_invoke_transport(srb = 0xFFFFFFC65D641438, > us = 0xFFFFFFC660447460) > -010|usb_stor_transparent_scsi_command(?, ?) > -011|usb_stor_control_thread(__us = 0xFFFFFFC660447460) //us->dev_mutex > -012|kthread(_create = 0xFFFFFFC6604C5E80) > -013|ret_from_fork(asm) > ---|end of frame > > Below is the call stack of the task which trying to acquire the same > mutex(0xFFFFFFC660447460) in the error handling path. > > B::v.f_/task_0xFFFFFFC6609AA1C0 > -000|__switch_to(prev = 0xFFFFFFC6609AA1C0, ?) > -001|prepare_lock_switch(inline) > -001|context_switch(inline) > -001|__schedule(?) > -002|schedule() > -003|schedule_preempt_disabled() > -004|__mutex_lock_common(lock = 0xFFFFFFC660447460, state = 2, ?, ?, ?, > ?, ?) > -005|__mutex_lock_slowpath(?) > -006|__cmpxchg_acq(inline) > -006|__mutex_trylock_fast(inline) > -006|mutex_lock(lock = 0xFFFFFFC660447460) //us->dev_mutex > -007|device_reset(?) > -008|scsi_try_bus_device_reset(inline) > -008|scsi_eh_bus_device_reset(inline) > -008|scsi_eh_ready_devs(shost = 0xFFFFFFC660446C80, > work_q = 0xFFFFFF80191C3DE8, done_q = 0xFFFFFF80191C3DD8) > -009|scsi_error_handler(data = 0xFFFFFFC660446C80) > -010|kthread(_create = 0xFFFFFFC66042C080) > -011|ret_from_fork(asm) > ---|end of frame > > Fix this by adding 5 seconds timeout while waiting for completion. > > Fixes: 3e35bf39e (USB: fix codingstyle issues in drivers/usb/core/message.c) Please read the documentation for how to properly add a Fixes: line (hint, your sha1 isn't big enough.) And does this really "fix" a commit that chnaged the coding style? I doubt that... > Cc: [email protected] > Signed-off-by: Pratham Pratap <[email protected]> > --- > drivers/usb/core/message.c | 12 ++++++++---- > 1 file changed, 8 insertions(+), 4 deletions(-) > > diff --git a/drivers/usb/core/message.c b/drivers/usb/core/message.c > index ae1de9c..b1e839c 100644 > --- a/drivers/usb/core/message.c > +++ b/drivers/usb/core/message.c > @@ -515,15 +515,13 @@ EXPORT_SYMBOL_GPL(usb_sg_init); > */ > void usb_sg_wait(struct usb_sg_request *io) > { > - int i; > + int i, retval; > int entries = io->entries; > > /* queue the urbs. */ > spin_lock_irq(&io->lock); > i = 0; > while (i < entries && !io->status) { > - int retval; > - > io->urbs[i]->dev = io->dev; > spin_unlock_irq(&io->lock); > > @@ -569,7 +567,13 @@ void usb_sg_wait(struct usb_sg_request *io) > * So could the submit loop above ... but it's easier to > * solve neither problem than to solve both! > */ > - wait_for_completion(&io->complete); > + retval = wait_for_completion_timeout(&io->complete, > + msecs_to_jiffies(5000)); Where did you pick 5 seconds from? Are you sure that will work properly? What about devices with very long i/o stalls when data is being flushed out, are you sure this will not trigger there? > + if (retval == 0) { > + dev_err(&io->dev->dev, "%s, timed out while waiting for > io_complete\n", > + __func__); > + usb_sg_cancel(io); So this is cancelled, but how does userspace know the error happened and it was a timeout? thanks, greg k-h
