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) -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) Cc: stable@vger.kernel.org Signed-off-by: Pratham Pratap prathampratap@codeaurora.org --- 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)); + if (retval == 0) { + dev_err(&io->dev->dev, "%s, timed out while waiting for io_complete\n", + __func__); + usb_sg_cancel(io); + }
sg_clean(io); }
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: stable@vger.kernel.org Signed-off-by: Pratham Pratap prathampratap@codeaurora.org
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
On Tue, Oct 13, 2020 at 04:17:02PM +0530, Pratham Pratap wrote:
...
Fixes: 3e35bf39e (USB: fix codingstyle issues in drivers/usb/core/message.c)
Two hints how to use Git with Linux kernel development.
First is about what Greg pointed out, i.e. proper Fixes line.
Add to your ~/.gitconfig the following:
[core] abbrev = 12
[alias] one = show -s --pretty='format:%h ("%s")'
In result you may run
git one 3e35bf39e
and use the output.
Second one is about Cc list. I recommend to use
scripts/get_maintainer.pl --git --git-min-percent=67
to retrieve it.
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
Are you talking about usb-storage? You should describe the context better -- judging by the patch title, it looks like you're talking about a core driver instead.
the device reset handler which is trying to acquire the same mutex causing a deadlock situation.
That isn't supposed to happen. The SCSI error handler should always cancel all the outstanding commands before invoking the device reset handler. Cancelling the commands will cause the URBs to complete.
If you found a test case where this doesn't happen, it probably means there's a bug in the SCSI core code or the USB host controller driver. That bug should be fixed; don't introduce random timeout values to try and work around it.
Alan Stern
linux-stable-mirror@lists.linaro.org
-
Alan Stern -
Andy Shevchenko -
Greg KH -
Pratham Pratap