linux-kernel - [PATCH] dm-region-hash: fix strange usage of mempool

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Date:   Mon, 10 Apr 2017 12:11:06 +1000
From:   NeilBrown <neilb@...e.com>
To:     Alasdair Kergon <agk@...hat.com>, Mike Snitzer <snitzer@...hat.com>
Cc:     dm-devel@...hat.com, linux-kernel@...r.kernel.org
Subject: [PATCH] dm-region-hash: fix strange usage of mempool_alloc.

mempool_alloc() should only be called with GFP_ATOMIC when
it is not safe to wait. Passing __GFP_NOFAIL to kmalloc()
says that it is safe to wait indefinitely.  So this code is
inconsistent.

Clearly it is OK to wait indefinitely in this code, and
mempool_alloc() is able to do that.  So just use
mempool_alloc, and allow it to sleep.  If no memory is
available it will wait for something to be returned to the
pool, and will retry a normal allocation regularly.

Signed-off-by: NeilBrown <neilb@...e.com>
---
 drivers/md/dm-region-hash.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/drivers/md/dm-region-hash.c b/drivers/md/dm-region-hash.c
index 85c32b22a420..a6279f5d779e 100644
--- a/drivers/md/dm-region-hash.c
+++ b/drivers/md/dm-region-hash.c
@@ -287,9 +287,7 @@ static struct dm_region *__rh_alloc(struct dm_region_hash *rh, region_t region)
 {
 	struct dm_region *reg, *nreg;

-	nreg = mempool_alloc(rh->region_pool, GFP_ATOMIC);
-	if (unlikely(!nreg))
-		nreg = kmalloc(sizeof(*nreg), GFP_NOIO | __GFP_NOFAIL);
+	nreg = mempool_alloc(rh->region_pool, GFP_NOIO);

 	nreg->state = rh->log->type->in_sync(rh->log, region, 1) ?
 		      DM_RH_CLEAN : DM_RH_NOSYNC;
-- 
2.12.2

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