[dm-devel] [PATCH]dm-mpath: fix for race condition between multipath_dtr and pg_init_done.

[Mikulas Patocka]

> Thanks for your comments.  I agree we should lock while setting 
> dtr_in_progress,

You can use spinlock when you read or write the variable.

Or - without locking, you can use memory barriers - put smp_mb() after you 
write dtr_in_progress and before you read it. Use 
ACCESS_ONCE(m->dtr_in_progress) in the if statement where you read 
dtr_in_progress.

Mikulas

> I think I overlooked it as its handled in process_queued_ios as well. We 
> looked into handling this in wait_for_pg_init_completion() but checking 
> for pg_init_required here will not help as well ( until we prevent 
> setting pg_init_required while pg_init_in_progress is set ). Here due to 
> SCSI_DH_RETRY on mode_select, pg_init_done will set the pg_init_required 
> as activation needs to be retried under normal circumstances. But it 
> completely differs when multipath target is being destroyed.  
> Apparently I didn't see any pending_ios in our test while this is 
> happening. Just path activations are held up since controller was 
> returning 5/91/36 CC's. With this condition either one of 
> pg_init_required or pg_init_in_progress flags are set all the time. 
> Hannes patch will take care of preventing queueing of IO's when 
> pg_init_in_progress is set, but currently running activation commands 
> will not return until controller returns SUCCESS on mode_select.
> 
>