Re: [PATCH v3 07/23] ata: libata-scsi: Fix delayed scsi_rescan_device() execution

[Hannes Reinecke <hare@suse.de>]

On 9/15/23 10:14, 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 scsi_rescan_device() are
>     not atomic and a suspend PM event may be triggered between them,
>     casuing scsi_rescan_device() to be called on a suspended device and
>     in that function blocking while holding the scsi device lock. This
>     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
> return value given by scsi_rescan_device() as that function will fail if
> called against a suspended device. Also make sure rescan tasks already
> scheduled are first cancelled before suspending an ata port.
> 
> Fixes: 6aa0365a3c85 ("ata: libata-scsi: Avoid deadlock on rescan after device resume")
> Cc: stable@vger.kernel.org
> Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
> ---
>   drivers/ata/libata-core.c | 16 ++++++++++++++++
>   drivers/ata/libata-scsi.c | 33 +++++++++++++++------------------
>   2 files changed, 31 insertions(+), 18 deletions(-)
> 
Reviewed-by: Hannes Reinecke <hare@suse.de>

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		           Kernel Storage Architect
hare@suse.de			                  +49 911 74053 688
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