linux-kernel - Re: [PATCH V2 2/2] fs/super.c: don't fool lockdep in freeze_super() and thaw

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Message-ID: <20161005164432.GB15121@redhat.com>
Date:   Wed, 5 Oct 2016 18:44:32 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Dave Chinner <david@...morbit.com>
Cc:     Jan Kara <jack@...e.cz>, Al Viro <viro@...iv.linux.org.uk>,
        Nikolay Borisov <kernel@...p.com>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        fstests@...r.kernel.org
Subject: Re: [PATCH V2 2/2] fs/super.c: don't fool lockdep in freeze_super()
 and thaw_super() paths

On 10/05, Dave Chinner wrote:
>
> On Tue, Oct 04, 2016 at 01:43:43PM +0200, Oleg Nesterov wrote:
>
> > plus the following warnings:
> >
> > 	[ 1894.500040] run fstests generic/070 at 2016-10-04 05:03:39
> > 	[ 1895.076655] =================================
> > 	[ 1895.077136] [ INFO: inconsistent lock state ]
> > 	[ 1895.077574] 4.8.0 #1 Not tainted
> > 	[ 1895.077900] ---------------------------------
> > 	[ 1895.078330] inconsistent {IN-RECLAIM_FS-W} -> {RECLAIM_FS-ON-W} usage.
> > 	[ 1895.078993] fsstress/18239 [HC0[0]:SC0[0]:HE1:SE1] takes:
> > 	[ 1895.079522]  (&xfs_nondir_ilock_class){++++?-}, at: [<ffffffffc049ad45>] xfs_ilock+0x165/0x210 [xfs]
> > 	[ 1895.080529] {IN-RECLAIM_FS-W} state was registered at:
>
> And that is a bug in the lockdep annotations for memory allocation because it
> fails to take into account the current task flags that are set via
> memalloc_noio_save() to prevent vmalloc from doing GFP_KERNEL allocations. i.e.
> in _xfs_buf_map_pages():

OK, I see...

I'll re-test with the following change:

	--- a/kernel/locking/lockdep.c
	+++ b/kernel/locking/lockdep.c
	@@ -2867,7 +2867,7 @@ static void __lockdep_trace_alloc(gfp_t gfp_mask, unsigned long flags)
			return;
	 
		/* We're only interested __GFP_FS allocations for now */
	-       if (!(gfp_mask & __GFP_FS))
	+       if ((curr->flags & PF_MEMALLOC_NOIO) || !(gfp_mask & __GFP_FS))
			return;


Hmm. This is off-topic and most probably I missed something... but at
first glance we can simplify/improve the reclaim-fs lockdep annotations:

1. add the global "struct lockdep_map reclaim_fs_map"

2. change __lockdep_trace_alloc

	-	mark_held_locks(curr, RECLAIM_FS);
	+	lock_map_acquire(&reclaim_fs_map);
	+	lock_map_release(&reclaim_fs_map);

3. turn lockdep_set/clear_current_reclaim_state() into

	void lockdep_set_current_reclaim_state(gfp_t gfp_mask)
	{
		if (gfp_mask & __GFP_FS)
			lock_map_acquire(&reclaim_fs_map);
	}

	void lockdep_clear_current_reclaim_state(gfp_t gfp_mask)
	{
		if (gfp_mask & __GFP_FS)
			lock_map_release(&reclaim_fs_map);
	}

and now we can remove task_struct->lockdep_reclaim_gfp and all other
RECLAIM_FS hacks in lockdep.c. Plus we can easily extend this logic to
check more GFP_ flags.

No?

Oleg.