diff options
authorGabriel Krisman Bertazi <krisman@linux.vnet.ibm.com>2016-12-14 18:48:36 -0200
committerJens Axboe <axboe@fb.com>2016-12-14 13:57:47 -0700
commitd1b1cea1e58477dad88ff769f54c0d2dfa56d923 (patch)
parent36e1f3d107867b25c616c2fd294f5a1c9d4e5d09 (diff)
blk-mq: Fix failed allocation path when mapping queues
In blk_mq_map_swqueue, there is a memory optimization that frees the tags of a queue that has gone unmapped. Later, if that hctx is remapped after another topology change, the tags need to be reallocated. If this allocation fails, a simple WARN_ON triggers, but the block layer ends up with an active hctx without any corresponding set of tags. Then, any income IO to that hctx can trigger an Oops. I can reproduce it consistently by running IO, flipping CPUs on and off and eventually injecting a memory allocation failure in that path. In the fix below, if the system experiences a failed allocation of any hctx's tags, we remap all the ctxs of that queue to the hctx_0, which should always keep it's tags. There is a minor performance hit, since our mapping just got worse after the error path, but this is the simplest solution to handle this error path. The performance hit will disappear after another successful remap. I considered dropping the memory optimization all together, but it seemed a bad trade-off to handle this very specific error case. This should apply cleanly on top of Jens' for-next branch. The Oops is the one below: SP (3fff935ce4d0) is in userspace 1:mon> e cpu 0x1: Vector: 300 (Data Access) at [c000000fe99eb110] pc: c0000000005e868c: __sbitmap_queue_get+0x2c/0x180 lr: c000000000575328: __bt_get+0x48/0xd0 sp: c000000fe99eb390 msr: 900000010280b033 dar: 28 dsisr: 40000000 current = 0xc000000fe9966800 paca = 0xc000000007e80300 softe: 0 irq_happened: 0x01 pid = 11035, comm = aio-stress Linux version 4.8.0-rc6+ (root@bean) (gcc version 5.4.0 20160609 (Ubuntu/IBM 5.4.0-6ubuntu1~16.04.2) ) #3 SMP Mon Oct 10 20:16:53 CDT 2016 1:mon> s [c000000fe99eb3d0] c000000000575328 __bt_get+0x48/0xd0 [c000000fe99eb400] c000000000575838 bt_get.isra.1+0x78/0x2d0 [c000000fe99eb480] c000000000575cb4 blk_mq_get_tag+0x44/0x100 [c000000fe99eb4b0] c00000000056f6f4 __blk_mq_alloc_request+0x44/0x220 [c000000fe99eb500] c000000000570050 blk_mq_map_request+0x100/0x1f0 [c000000fe99eb580] c000000000574650 blk_mq_make_request+0xf0/0x540 [c000000fe99eb640] c000000000561c44 generic_make_request+0x144/0x230 [c000000fe99eb690] c000000000561e00 submit_bio+0xd0/0x200 [c000000fe99eb740] c0000000003ef740 ext4_io_submit+0x90/0xb0 [c000000fe99eb770] c0000000003e95d8 ext4_writepages+0x588/0xdd0 [c000000fe99eb910] c00000000025a9f0 do_writepages+0x60/0xc0 [c000000fe99eb940] c000000000246c88 __filemap_fdatawrite_range+0xf8/0x180 [c000000fe99eb9e0] c000000000246f90 filemap_write_and_wait_range+0x70/0xf0 [c000000fe99eba20] c0000000003dd844 ext4_sync_file+0x214/0x540 [c000000fe99eba80] c000000000364718 vfs_fsync_range+0x78/0x130 [c000000fe99ebad0] c0000000003dd46c ext4_file_write_iter+0x35c/0x430 [c000000fe99ebb90] c00000000038c280 aio_run_iocb+0x3b0/0x450 [c000000fe99ebce0] c00000000038dc28 do_io_submit+0x368/0x730 [c000000fe99ebe30] c000000000009404 system_call+0x38/0xec Signed-off-by: Gabriel Krisman Bertazi <krisman@linux.vnet.ibm.com> Cc: Brian King <brking@linux.vnet.ibm.com> Cc: Douglas Miller <dougmill@linux.vnet.ibm.com> Cc: linux-block@vger.kernel.org Cc: linux-scsi@vger.kernel.org Reviewed-by: Douglas Miller <dougmill@linux.vnet.ibm.com> Signed-off-by: Jens Axboe <axboe@fb.com>
1 files changed, 21 insertions, 5 deletions
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 7ad7c11fe01d..4bf850e8d6b5 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1870,7 +1870,7 @@ static void blk_mq_init_cpu_queues(struct request_queue *q,
static void blk_mq_map_swqueue(struct request_queue *q,
const struct cpumask *online_mask)
- unsigned int i;
+ unsigned int i, hctx_idx;
struct blk_mq_hw_ctx *hctx;
struct blk_mq_ctx *ctx;
struct blk_mq_tag_set *set = q->tag_set;
@@ -1893,6 +1893,21 @@ static void blk_mq_map_swqueue(struct request_queue *q,
if (!cpumask_test_cpu(i, online_mask))
+ hctx_idx = q->mq_map[i];
+ /* unmapped hw queue can be remapped after CPU topo changed */
+ if (!set->tags[hctx_idx]) {
+ set->tags[hctx_idx] = blk_mq_init_rq_map(set, hctx_idx);
+ /*
+ * If tags initialization fail for some hctx,
+ * that hctx won't be brought online. In this
+ * case, remap the current ctx to hctx[0] which
+ * is guaranteed to always have tags allocated
+ */
+ if (!set->tags[hctx_idx])
+ q->mq_map[i] = 0;
+ }
ctx = per_cpu_ptr(q->queue_ctx, i);
hctx = blk_mq_map_queue(q, i);
@@ -1909,7 +1924,11 @@ static void blk_mq_map_swqueue(struct request_queue *q,
* disable it and free the request entries.
if (!hctx->nr_ctx) {
- if (set->tags[i]) {
+ /* Never unmap queue 0. We need it as a
+ * fallback in case of a new remap fails
+ * allocation
+ */
+ if (i && set->tags[i]) {
blk_mq_free_rq_map(set, set->tags[i], i);
set->tags[i] = NULL;
@@ -1917,9 +1936,6 @@ static void blk_mq_map_swqueue(struct request_queue *q,
- /* unmapped hw queue can be remapped after CPU topo changed */
- if (!set->tags[i])
- set->tags[i] = blk_mq_init_rq_map(set, i);
hctx->tags = set->tags[i];