linux-kernel - [PATCH] blk-cgroup: use __GFP_NOWARN for NOWAIT allocations

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Date:   Tue, 25 Oct 2016 13:44:32 +0200
From:   Christian Borntraeger <borntraeger@...ibm.com>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        Christian Borntraeger <borntraeger@...ibm.com>
Subject: [PATCH] blk-cgroup: use __GFP_NOWARN for NOWAIT allocations

I just got

qemu-system-s39: page allocation failure: order:0, mode:0x2200000(GFP_NOWAIT|__GFP_NOTRACK)
CPU: 0 PID: 6664 Comm: qemu-system-s39 Tainted: G 4.9.0-rc2+ #44
[...]
([<000000000011230a>] show_trace+0x62/0x78)
([<00000000001123da>] show_stack+0x72/0xf0)
([<00000000004a7906>] dump_stack+0x7e/0xb0)
([<000000000025df14>] warn_alloc+0x11c/0x148)
([<000000000025e48c>] __alloc_pages_nodemask+0x4c4/0xe50)
([<00000000002be590>] new_slab+0x560/0x778
([<00000000002c0adc>] ___slab_alloc.constprop.29+0x2b4/0x368)
([<00000000002c0bc4>] __slab_alloc.constprop.28+0x34/0x50)
([<00000000002c10aa>] kmem_cache_alloc_trace+0x20a/0x270)
([<0000000000257934>] mempool_create_node+0x5c/0x188)
([<00000000004745d6>] blk_init_rl+0xa6/0xe0)
([<0000000000493f58>] blkg_alloc+0x150/0x2a8)
([<0000000000494404>] blkg_create+0x354/0x3b0)
([<00000000004962c0>] blkg_lookup_create+0x100/0x180)
([<0000000000472cd4>] generic_make_request_checks+0x504/0x590)
([<0000000000474a66>] generic_make_request+0x2e/0x1b0)
([<0000000000474c8c>] submit_bio+0xa4/0x178)
([<000003ff80c64670>] btrfs_map_bio+0x1c0/0x3c8 [btrfs])
([<000003ff80c3075c>] btrfs_submit_bio_hook+0x104/0x210
[...]

Seems that blk-cgroup can handle allocation failures quite will - it
does check the result and the system continues to run, so let's make
allocation failures silent in here.

There are other GFP_NOWAIT places in that file, but not all seem to
check the return value. In addition this warning seems to be the only
one that I can reliably reproduce so I decided to only touch
blkg_create.

Signed-off-by: Christian Borntraeger <borntraeger@...ibm.com>
---
 block/blk-cgroup.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index b08ccbb..d22bd95 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -185,7 +185,8 @@ static struct blkcg_gq *blkg_create(struct blkcg *blkcg,
 	}
 
 	wb_congested = wb_congested_get_create(&q->backing_dev_info,
-					       blkcg->css.id, GFP_NOWAIT);
+					       blkcg->css.id,
+					       GFP_NOWAIT | __GFP_NOWARN);
 	if (!wb_congested) {
 		ret = -ENOMEM;
 		goto err_put_css;
@@ -193,7 +194,7 @@ static struct blkcg_gq *blkg_create(struct blkcg *blkcg,
 
 	/* allocate */
 	if (!new_blkg) {
-		new_blkg = blkg_alloc(blkcg, q, GFP_NOWAIT);
+		new_blkg = blkg_alloc(blkcg, q, GFP_NOWAIT | __GFP_NOWARN);
 		if (unlikely(!new_blkg)) {
 			ret = -ENOMEM;
 			goto err_put_congested;
-- 
2.5.5