linux-kernel - [PATCH v3] lockdep: Teach lockdep about memalloc_noio

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Date:   Wed,  1 Mar 2017 13:29:57 +0200
From:   Nikolay Borisov <nborisov@...e.com>
To:     peterz@...radead.org
Cc:     linux-kernel@...r.kernel.org, mhocko@...nel.org,
        vbabka.lkml@...il.com, linux-mm@...ck.org, mingo@...hat.com,
        Nikolay Borisov <nborisov@...e.com>
Subject: [PATCH v3] lockdep: Teach lockdep about memalloc_noio_save

Commit 21caf2fc1931 ("mm: teach mm by current context info to not do I/O
during memory allocation") added the memalloc_noio_(save|restore) functions
to enable people to modify the MM behavior by disbaling I/O during memory
allocation. This was further extended in Fixes: 934f3072c17c ("mm: clear 
__GFP_FS when PF_MEMALLOC_NOIO is set"). memalloc_noio_* functions prevent 
allocation paths recursing back into the filesystem without explicitly 
changing the flags for every allocation site. However, lockdep hasn't been 
keeping up with the changes and it entirely misses handling the memalloc_noio
adjustments. Instead, it is left to the callers of __lockdep_trace_alloc to 
call the functino after they have shaven the respective GFP flags. 

Let's fix this by making lockdep explicitly do the shaving of respective
GFP flags. 

Fixes: 934f3072c17c ("mm: clear __GFP_FS when PF_MEMALLOC_NOIO is set")
Signed-off-by: Nikolay Borisov <nborisov@...e.com>
---
 kernel/locking/lockdep.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

Changes since v2: 
	* Incorporate Michal's suggestion of using memalloc_noio_flags explicitly. 
	* Tune the commit message to make the problem statement a bit more
	descriptive. 

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 9812e5dd409e..565506c9e99c 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -2861,6 +2861,8 @@ static void __lockdep_trace_alloc(gfp_t gfp_mask, unsigned long flags)
 	if (unlikely(!debug_locks))
 		return;

+	gfp_mask = memalloc_noio_flags(gfp_mask);
+
 	/* no reclaim without waiting on it */
 	if (!(gfp_mask & __GFP_DIRECT_RECLAIM))
 		return;
@@ -3852,7 +3854,7 @@ EXPORT_SYMBOL_GPL(lock_unpin_lock);

 void lockdep_set_current_reclaim_state(gfp_t gfp_mask)
 {
-	current->lockdep_reclaim_gfp = gfp_mask;
+	current->lockdep_reclaim_gfp = memalloc_noio_flags(gfp_mask);
 }

 void lockdep_clear_current_reclaim_state(void)
-- 
2.7.4