Re: SCSI EH wakeup deadlock from deferred_qc

[Damien Le Moal <dlemoal@kernel.org>]

On 7/9/26 04:36, Igor Pylypiv wrote:
> Hi Damien,
> 
> I've stumbled upon an issue where SCSI EH didn't run upon command timeout
> but ran ~10 or so seconds later. It seems like a recent regression from
> the introduction of deffered_qc.
> 
> When an active command times out while a non-NCQ command is waiting in
> deferred_qc, SCSI EH fails to wake up. Recovery stalls until the deferred
> command's own timer expires.
> 
> When an NCQ command times out, scsi_timeout() calls scsi_eh_scmd_add(),
> incrementing shost->host_failed (1). However, when scsi_eh_wakeup() checks
> whether to wake the EH thread, scsi_host_busy(shost) counts 2 active
> commands (1 timed-out + 1 in deferred_qc).
> 
> Because busy (2) != host_failed (1), scsi_eh_wakeup() refuses to wake
> the EH thread, deadlocking error recovery until the deferred command
> times out on its own.

Igor,

Thank you for reporting this. Let me have a look.


-- 
Damien Le Moal
Western Digital Research