Re: [PATCH] SCSI: Fix hard lockup in scsi_remove_target()

Johannes Thumshirn
2015-10-02T13:09:37Z

Christoph Hellwig <hch@infradead.org> writes:

>> - list_for_each_entry(starget, &shost->__targets, siblings) {
>> + list_for_each_entry_safe(starget, tmp, &shost->__targets, siblings) {
>> if (starget->state == STARGET_DEL)
>> continue;
>> if (starget->dev.parent == dev || &starget->dev == dev) {
>> /* assuming new targets arrive at the end */
>
> Now that the last variable is gone this comments isn't needed.

Yep, you're right. I'll remove it.

>
>> kref_get(&starget->reap_ref);
>> spin_unlock_irqrestore(shost->host_lock, flags);
>> - if (last)
>> - scsi_target_reap(last);
>> - last = starget;
>> +
>> __scsi_remove_target(starget);
>> + list_move_tail(&starget->siblings, &reap_list);
>> spin_lock_irqsave(shost->host_lock, flags);
>> }
>
> What makes the list_move save after dropping host_lock? I think this
> needs to be changed to not drop the host_lock and change
> __scsi_remove_target to expect host_lock held to be safe.

Having the list_move() outside of the host_lock was purely by
accident. Interestingly the stressing didn't mind it. But yes you're
right, __scsi_remove_target() should be made host_lock() save for being
called under the host_lock.

Regarding the list move, does it look OK for you (i.e. do we still need
it after reworking __scsi_remove_target())? IMHO yes, but I only have
half a year of experience in this area).

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