[PATCH] usb: core: Don't wait for completion of urbs

[Pratham Pratap <prathampratap@codeaurora.org>]

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);
 }
-- 
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