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Date: Wed, 18 Feb 2015 19:03:53 +0100
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: linux-rt-users@...r.kernel.org
Cc: linux-kernel@...r.kernel.org,
Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: [PATCH RT] block/mq: drop per ctx cpu_lock
While converting the get_cpu() to get_cpu_light() I added a cpu lock to
ensure the same code is not invoked twice on the same CPU. And now I run
into this:
| kernel BUG at kernel/locking/rtmutex.c:996!
| invalid opcode: 0000 [#1] PREEMPT SMP
| CPU0: 13 PID: 75 Comm: kworker/u258:0 Tainted: G I 3.18.7-rt1.5+ #12
| Workqueue: writeback bdi_writeback_workfn (flush-8:0)
| task: ffff88023742a620 ti: ffff88023743c000 task.ti: ffff88023743c000
| RIP: 0010:[<ffffffff81523cc0>] [<ffffffff81523cc0>] rt_spin_lock_slowlock+0x280/0x2d0
| Call Trace:
| [<ffffffff815254e7>] rt_spin_lock+0x27/0x60
taking the same lock again
|
| [<ffffffff8127c771>] blk_mq_insert_requests+0x51/0x130
| [<ffffffff8127d4a9>] blk_mq_flush_plug_list+0x129/0x140
| [<ffffffff81272461>] blk_flush_plug_list+0xd1/0x250
| [<ffffffff81522075>] schedule+0x75/0xa0
| [<ffffffff8152474d>] do_nanosleep+0xdd/0x180
| [<ffffffff810c8312>] __hrtimer_nanosleep+0xd2/0x1c0
| [<ffffffff810c8456>] cpu_chill+0x56/0x80
| [<ffffffff8107c13d>] try_to_grab_pending+0x1bd/0x390
| [<ffffffff8107c431>] cancel_delayed_work+0x21/0x170
| [<ffffffff81279a98>] blk_mq_stop_hw_queue+0x18/0x40
| [<ffffffffa000ac6f>] scsi_queue_rq+0x7f/0x830 [scsi_mod]
| [<ffffffff8127b0de>] __blk_mq_run_hw_queue+0x1ee/0x360
| [<ffffffff8127b528>] blk_mq_map_request+0x108/0x190
take the lock ^^^
|
| [<ffffffff8127c8d2>] blk_sq_make_request+0x82/0x350
| [<ffffffff8126f6c0>] generic_make_request+0xd0/0x120
| [<ffffffff8126f788>] submit_bio+0x78/0x190
| [<ffffffff811bd537>] _submit_bh+0x117/0x180
| [<ffffffff811bf528>] __block_write_full_page.constprop.38+0x138/0x3f0
| [<ffffffff811bf880>] block_write_full_page+0xa0/0xe0
| [<ffffffff811c02b3>] blkdev_writepage+0x13/0x20
| [<ffffffff81127b25>] __writepage+0x15/0x40
| [<ffffffff8112873b>] write_cache_pages+0x1fb/0x440
| [<ffffffff811289be>] generic_writepages+0x3e/0x60
| [<ffffffff8112a17c>] do_writepages+0x1c/0x30
| [<ffffffff811b3603>] __writeback_single_inode+0x33/0x140
| [<ffffffff811b462d>] writeback_sb_inodes+0x2bd/0x490
| [<ffffffff811b4897>] __writeback_inodes_wb+0x97/0xd0
| [<ffffffff811b4a9b>] wb_writeback+0x1cb/0x210
| [<ffffffff811b505b>] bdi_writeback_workfn+0x25b/0x380
| [<ffffffff8107b50b>] process_one_work+0x1bb/0x490
| [<ffffffff8107c7ab>] worker_thread+0x6b/0x4f0
| [<ffffffff81081863>] kthread+0xe3/0x100
| [<ffffffff8152627c>] ret_from_fork+0x7c/0xb0
After looking at this for a while it seems that it is save if blk_mq_ctx is
used multiple times, the in struct lock protects the access.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
---
block/blk-mq.c | 4 ----
block/blk-mq.h | 8 --------
2 files changed, 12 deletions(-)
diff --git a/block/blk-mq.c b/block/blk-mq.c
index dce02cef145c..ec679b2c2229 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1272,9 +1272,7 @@ static void blk_sq_make_request(struct request_queue *q, struct bio *bio)
if (list_empty(&plug->mq_list))
trace_block_plug(q);
else if (request_count >= BLK_MAX_REQUEST_COUNT) {
- spin_unlock(&data.ctx->cpu_lock);
blk_flush_plug_list(plug, false);
- spin_lock(&data.ctx->cpu_lock);
trace_block_plug(q);
}
list_add_tail(&rq->queuelist, &plug->mq_list);
@@ -1470,7 +1468,6 @@ static int blk_mq_hctx_cpu_offline(struct blk_mq_hw_ctx *hctx, int cpu)
blk_mq_hctx_clear_pending(hctx, ctx);
}
spin_unlock(&ctx->lock);
- __blk_mq_put_ctx(ctx);
if (list_empty(&tmp))
return NOTIFY_OK;
@@ -1680,7 +1677,6 @@ static void blk_mq_init_cpu_queues(struct request_queue *q,
memset(__ctx, 0, sizeof(*__ctx));
__ctx->cpu = i;
spin_lock_init(&__ctx->lock);
- spin_lock_init(&__ctx->cpu_lock);
INIT_LIST_HEAD(&__ctx->rq_list);
__ctx->queue = q;
diff --git a/block/blk-mq.h b/block/blk-mq.h
index d0d4780ddfb6..d1d78dfe4123 100644
--- a/block/blk-mq.h
+++ b/block/blk-mq.h
@@ -9,7 +9,6 @@ struct blk_mq_ctx {
struct list_head rq_list;
} ____cacheline_aligned_in_smp;
- spinlock_t cpu_lock;
unsigned int cpu;
unsigned int index_hw;
@@ -77,7 +76,6 @@ static inline struct blk_mq_ctx *__blk_mq_get_ctx(struct request_queue *q,
struct blk_mq_ctx *ctx;
ctx = per_cpu_ptr(q->queue_ctx, cpu);
- spin_lock(&ctx->cpu_lock);
return ctx;
}
@@ -92,14 +90,8 @@ static inline struct blk_mq_ctx *blk_mq_get_ctx(struct request_queue *q)
return __blk_mq_get_ctx(q, get_cpu_light());
}
-static void __blk_mq_put_ctx(struct blk_mq_ctx *ctx)
-{
- spin_unlock(&ctx->cpu_lock);
-}
-
static inline void blk_mq_put_ctx(struct blk_mq_ctx *ctx)
{
- __blk_mq_put_ctx(ctx);
put_cpu_light();
}
--
2.1.4
--
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