On Mon, Sep 11, 2023 at 01:02:03PM +0900, Damien Le Moal wrote:
> Commit 6aa0365a3c85 ("ata: libata-scsi: Avoid deadlock on rescan after
> device resume") modified ata_scsi_dev_rescan() to check the scsi device
> "is_suspended" power field to ensure that the scsi device associated
> with an ATA device is fully resumed when scsi_rescan_device() is
> executed. However, this fix is problematic as:
> 1) it relies on a PM internal field that should not be used without PM
> device locking protection.
> 2) The check for is_suspended and the call to ata_scsi_dev_rescan() are
> not atomic and a suspend PM even may be triggered between them,
> casuing ata_scsi_dev_rescan() to be called on a suspended device,
> resulting in that function blocking while holding the scsi device
> lock, which would deadlock a following resume operation.
> These problems can trigger PM deadlocks on resume, especially with
> resume operations triggered quickly after or during suspend operations.
> E.g., a simple bash script like:
>
> for (( i=0; i<10; i++ )); do
> echo "+2 > /sys/class/rtc/rtc0/wakealarm
> echo mem > /sys/power/state
> done
>
> that triggers a resume 2 seconds after starting suspending a system can
> quickly lead to a PM deadlock preventing the system from correctly
> resuming.
>
> Fix this by replacing the check on is_suspended with a check on the scsi
> device state inside ata_scsi_dev_rescan(), while holding the scsi device
> lock, thus making the device rescan atomic with regard to PM operations.
> Additionnly, make sure that scheduled rescan tasks are first cancelled
> before suspending an ata port.
>
> Fixes: 6aa0365a3c85 ("ata: libata-scsi: Avoid deadlock on rescan after device resume")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Damien Le Moal <dlemoal@xxxxxxxxxx>
Tested-by: Chia-Lin Kao (AceLan) <acelan.kao@xxxxxxxxxxxxx>
