On 08/02/2018 03:09 AM, Chris Leech wrote: > On Wed, Aug 01, 2018 at 08:29:00AM +0200, Hannes Reinecke wrote: >> On 07/31/2018 07:56 PM, Chris Leech wrote: >>> The libfc and libfcoe modules look to have issues with mutexs being used >>> under rcu_read_lock, which triggers "Illegal context switch in RCU read >>> side critical section" warnings under debug kernels. >>> >>> I started looking at fc_disc.c where rport discovery code appears to >>> take a mutex for each rport in fc_rport_login/fc_rport_logoff while >>> being called under rcu_read_lock from fc_disc_done. >>> >>> With the rdata->kref held, I know rcu_read_unlock can be safely called >>> before login fc_rport_login/logoff. But I don't know if it's safe to >>> then recall rcu_read_lock and simply continue on with the >>> list_for_each_entry_rcu or not. >>> >>> And as I start looking into this one case, I also get the same class of >>> problem popping up in at least libfcoe:fcoe_ctrl.c from >>> fcoe_ctrl_timer_work as well :( >>> >> This should've been fixed by my patch series "libfc/fcoe: disc_mutex fixes". >> >> Can you check if this series is applied in your tree? > > Thanks, I missed those and they do fix things up! > > One question about "Add WARN_ON() when deleting rports" > >> --- a/drivers/scsi/libfc/fc_rport.c >> +++ b/drivers/scsi/libfc/fc_rport.c >> @@ -184,6 +184,7 @@ void fc_rport_destroy(struct kref *kref) >> struct fc_rport_priv *rdata; >> >> rdata = container_of(kref, struct fc_rport_priv, kref); >> + WARN_ON(!list_empty(&rdata->peers)); >> kfree_rcu(rdata, rcu); >> } >> EXPORT_SYMBOL(fc_rport_destroy); > > The list_head isn't reinitialized to make list_empty() return true after > list_del_rcu(), as there may still be readers traversing the list. > > So doesn't this warning trigger on every deleted rport? > Not that I've seen, but I'll check. Cheers, Hannes -- Dr. Hannes Reinecke Teamlead Storage & Networking hare@xxxxxxx +49 911 74053 688 SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg GF: F. Imendörffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton HRB 21284 (AG Nürnberg)
