> -----Original Message----- > From: Junichi Nomura [mailto:j-nomura@xxxxxxxxxxxxx] > Sent: Thursday, October 31, 2013 4:04 AM > To: device-mapper development; Merla, ShivaKrishna > Cc: agk@xxxxxxxxxx; snitzer@xxxxxxxxxx > Subject: Re: [PATCH][RESEND]dm-mpath: fix for race condition > between multipath_dtr and pg_init_done. > > On 10/30/13 12:26, Merla, ShivaKrishna wrote: > > Whenever multipath_dtr is happening, we should prevent queueing any > further path > > activation work. There was a kernel panic where after pg_init_done() > decrements > > pg_init_in_progress to 0, wait_for_pg_init_completion call assumes there > are no > > more pending path management commands. But if pg_init_required is set > by > > pg_init_done call due to retriable mode_select errors , then > process_queued_ios() > > will again queue the path activation work. If free_multipath call has been > > completed by the time activate_path work is called, kernel panic was seen > on > > accessing multipath members. > > > > BUG: unable to handle kernel NULL pointer dereference at > 0000000000000090 > > RIP: 0010:[<ffffffffa003db1b>] [<ffffffffa003db1b>] > activate_path+0x1b/0x30 [dm_multipath] > > [<ffffffff81090ac0>] worker_thread+0x170/0x2a0 > > [<ffffffff81096c80>] ? autoremove_wake_function+0x0/0x40 > > > > Signed-off-by: Shiva Krishna Merla<shivakrishna.merla@xxxxxxxxxx> > > Reviewed-by: Krishnasamy > Somasundaram<somasundaram.krishnasamy@xxxxxxxxxx> > > Tested-by: Speagle Andy<Andy.Speagle@xxxxxxxxxx> > > > > --- > > --- a/drivers/md/dm-mpath.c 2013-01-29 10:12:10.000000000 -0600 > > +++ b/drivers/md/dm-mpath.c 2013-10-29 21:02:03.267685017 -0500 > > @@ -73,6 +73,7 @@ struct multipath { > > > > wait_queue_head_t pg_init_wait; /* Wait for pg_init > completion */ > > > > + unsigned dtr_in_progress; /* multipath destroy in progress */ > > unsigned pg_init_required; /* pg_init needs calling? */ > > unsigned pg_init_in_progress; /* Only one pg_init allowed at once > */ > > unsigned pg_init_delay_retry; /* Delay pg_init retry? */ > > @@ -498,7 +499,8 @@ static void process_queued_ios(struct wo > > (!pgpath && !m->queue_if_no_path)) > > must_queue = 0; > > > > - if (m->pg_init_required && !m->pg_init_in_progress && pgpath) > > + if (m->pg_init_required && !m->pg_init_in_progress && pgpath && > > + !m->dtr_in_progress) > > __pg_init_all_paths(m); > > > > spin_unlock_irqrestore(&m->lock, flags); > > @@ -951,6 +953,11 @@ static void flush_multipath_work(struct > > static void multipath_dtr(struct dm_target *ti) > > { > > struct multipath *m = ti->private; > > + unsigned long flags; > > + > > + spin_lock_irqsave(&m->lock, flags); > > + m->dtr_in_progress = 1; > > + spin_unlock_irqrestore(&m->lock, flags); > > Hi, > > how about moving this to flush_multipath_work(), which is supposed > to silence background activities? > I.e. > flush_multipath_work() { > <disable pg_init retry> > ... > <enable pg_init retry> > } > > Then it not only fixes the crash you hit, it also fixes the hidden bug > that pg_init continues retrying while the device is suspended. We looked into adding checks for pg_init_required as well in multipath_wait_for_pg_init_completion(), but none of these will prevent pg_init_limit_reached() i.e from pg_init_done() from setting pg_init_required. >From code I see we end up waiting indefinitely for its completion. The reason for adding check in process_queued_ios() is __choose_pgpath() might again trigger pg_init_required and end up calling __pg_init_all_paths() which will unset pg_init_required and sets pg_init_in_progress within a lock. Also I believe the patch given above will prevent further path activations and no work will be queued again with dtr_in_progress. With Hannes patch IO's will not be queued in when pg_init_in_progress so we are clean there as well. Let me know your thoughts. -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
