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scsi: ufs: Fix hardware race conditions while aborting a command
There is a possible race condition in the hardware when the abort
command is issued to terminate the ongoing SCSI command as described
below:
- A bit in the door-bell register is set in the controller for a
new SCSI command.
- In some rare situations, before controller get a chance to issue
the command to the device, the software issued an abort command.
- If the device recieves abort command first then it returns success
because the command itself is not present.
- Now if the controller commits the command to device it will be
processed.
- Software thinks that command is aborted and proceed while still
the device is processing it.
- The software, controller and device may go out of sync because of
this race condition.
To avoid this, query task presence in the device before sending abort
task command so that after the abort operation, the command is guaranteed
to be non-existent in both controller and the device.
Signed-off-by: Sujit Reddy Thumma <sthumma@codeaurora.org>
Reviewed-by: Yaniv Gardi <ygardi@codeaurora.org>
Tested-by: Dolev Raviv <draviv@codeaurora.org>
Acked-by: Vinayak Holikatti <vinholikatti@gmail.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>