Re: sleeping function warning from __put_anon_vma

[Hugh Dickins <hughd@google.com>]

On Thu, 29 May 2014, Dave Jones wrote:

> BUG: sleeping function called from invalid context at kernel/locking/rwsem.c:47
> in_atomic(): 0, irqs_disabled(): 0, pid: 5787, name: trinity-c27
> Preemption disabled at:[<ffffffff990acc7e>] vtime_account_system+0x1e/0x50
> CPU: 0 PID: 5787 Comm: trinity-c27 Not tainted 3.15.0-rc7+ #219
>  ffffffff99a47203 0000000099b50bef ffff880239f138c8 ffffffff99739dfb
>  0000000000000000 ffff880239f138f0 ffffffff990a026c ffff8801078b5458
>  ffff8801078b5450 ffffea00044be980 ffff880239f13908 ffffffff99741c30
> Call Trace:
>  [<ffffffff99739dfb>] dump_stack+0x4e/0x7a
>  [<ffffffff990a026c>] __might_sleep+0x11c/0x1b0
>  [<ffffffff99741c30>] down_write+0x20/0x40
>  [<ffffffff9919337d>] __put_anon_vma+0x3d/0xc0
>  [<ffffffff99193998>] page_get_anon_vma+0x68/0xb0
>  [<ffffffff991b97e9>] migrate_pages+0x449/0x880
>  [<ffffffff9917dc00>] ? isolate_freepages_block+0x360/0x360
>  [<ffffffff9917ec8a>] compact_zone+0x38a/0x580
>  [<ffffffff9917ef29>] compact_zone_order+0xa9/0x130
>  [<ffffffff9917f329>] try_to_compact_pages+0xe9/0x140
>  [<ffffffff991616da>] __alloc_pages_direct_compact+0x7a/0x250
>  [<ffffffff99161fbb>] __alloc_pages_nodemask+0x70b/0xbb0
>  [<ffffffff991a9c3f>] alloc_pages_vma+0xaf/0x1c0
>  [<ffffffff991bdc8d>] do_huge_pmd_anonymous_page+0xed/0x3d0
>  [<ffffffff991871b4>] handle_mm_fault+0x1b4/0xc50
>  [<ffffffff9974358d>] ? retint_restore_args+0xe/0xe
>  [<ffffffff99746939>] __do_page_fault+0x1c9/0x630
>  [<ffffffff99118acb>] ? __acct_update_integrals+0x8b/0x120
>  [<ffffffff9974725b>] ? preempt_count_sub+0xab/0x100
>  [<ffffffff99746dbe>] do_page_fault+0x1e/0x70
>  [<ffffffff997437f2>] page_fault+0x22/0x30

Well caught again.  This one doesn't seem to have been plaguing users,
but nice to find and fix it.  I don't think there are any gotchas to
the patch below (in each case we've done a good atomic_inc_not_zero,
so the anon_vma cannot be surprisingly freed when we rcu_read_unlock).
But even so, I don't think it should go into a tree without Ack from
Peter - in looking back there, he might notice something else has
changed, or be inspired to fix it in a more satisfying way.

Hugh

[PATCH] mm: fix sleeping function warning from __put_anon_vma

Trinity reports BUG:
sleeping function called from invalid context at kernel/locking/rwsem.c:47
in_atomic(): 0, irqs_disabled(): 0, pid: 5787, name: trinity-c27
__might_sleep < down_write < __put_anon_vma < page_get_anon_vma <
migrate_pages < compact_zone < compact_zone_order < try_to_compact_pages ..

Right, since conversion to mutex then rwsem, we should not put_anon_vma()
from inside an rcu_read_lock()ed section: fix the two places that did so.

Fixes: 88c22088bf23 ("mm: optimize page_lock_anon_vma() fast-path")
Reported-by: Dave Jones <davej@redhat.com>
Signed-off-by: Hugh Dickins <hughd@google.com>
Needs-Ack-from: Peter Zijlstra <peterz@infradead.org>
---

 mm/rmap.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

--- 3.15-rc7/mm/rmap.c	2014-04-13 17:24:36.680507189 -0700
+++ linux/mm/rmap.c	2014-05-31 12:02:08.496088637 -0700
@@ -426,12 +426,14 @@ struct anon_vma *page_get_anon_vma(struc
 	 * above cannot corrupt).
 	 */
 	if (!page_mapped(page)) {
+		rcu_read_unlock();
 		put_anon_vma(anon_vma);
 		anon_vma = NULL;
+		goto outer;
 	}
 out:
 	rcu_read_unlock();
-
+outer:
 	return anon_vma;
 }
 
@@ -477,9 +479,10 @@ struct anon_vma *page_lock_anon_vma_read
 	}
 
 	if (!page_mapped(page)) {
+		rcu_read_unlock();
 		put_anon_vma(anon_vma);
 		anon_vma = NULL;
-		goto out;
+		goto outer;
 	}
 
 	/* we pinned the anon_vma, its safe to sleep */
@@ -501,6 +504,7 @@ struct anon_vma *page_lock_anon_vma_read
 
 out:
 	rcu_read_unlock();
+outer:
 	return anon_vma;
 }
 

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