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authorMing Lei <ming.lei@redhat.com>2020-05-29 15:53:15 +0200
committerJens Axboe <axboe@kernel.dk>2020-05-29 10:23:25 -0600
commitbf0beec0607db3c6f6fb7bd2c6d503792b05cf3f (patch)
tree10b8e3b1cc69eb2e8b4f23cc176726c371d2c239 /block/blk-mq-tag.c
parent602380d28e28b454683efac41dc4b2862d055d91 (diff)
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blk-mq: drain I/O when all CPUs in a hctx are offline
Most of blk-mq drivers depend on managed IRQ's auto-affinity to setup up queue mapping. Thomas mentioned the following point[1]: "That was the constraint of managed interrupts from the very beginning: The driver/subsystem has to quiesce the interrupt line and the associated queue _before_ it gets shutdown in CPU unplug and not fiddle with it until it's restarted by the core when the CPU is plugged in again." However, current blk-mq implementation doesn't quiesce hw queue before the last CPU in the hctx is shutdown. Even worse, CPUHP_BLK_MQ_DEAD is a cpuhp state handled after the CPU is down, so there isn't any chance to quiesce the hctx before shutting down the CPU. Add new CPUHP_AP_BLK_MQ_ONLINE state to stop allocating from blk-mq hctxs where the last CPU goes away, and wait for completion of in-flight requests. This guarantees that there is no inflight I/O before shutting down the managed IRQ. Add a BLK_MQ_F_STACKING and set it for dm-rq and loop, so we don't need to wait for completion of in-flight requests from these drivers to avoid a potential dead-lock. It is safe to do this for stacking drivers as those do not use interrupts at all and their I/O completions are triggered by underlying devices I/O completion. [1] https://lore.kernel.org/linux-block/alpine.DEB.2.21.1904051331270.1802@nanos.tec.linutronix.de/ [hch: different retry mechanism, merged two patches, minor cleanups] Signed-off-by: Ming Lei <ming.lei@redhat.com> Signed-off-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Hannes Reinecke <hare@suse.de> Reviewed-by: Daniel Wagner <dwagner@suse.de> Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'block/blk-mq-tag.c')
-rw-r--r--block/blk-mq-tag.c8
1 files changed, 8 insertions, 0 deletions
diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index 762198b62088..96a39d0724a2 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -180,6 +180,14 @@ unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data)
sbitmap_finish_wait(bt, ws, &wait);
found_tag:
+ /*
+ * Give up this allocation if the hctx is inactive. The caller will
+ * retry on an active hctx.
+ */
+ if (unlikely(test_bit(BLK_MQ_S_INACTIVE, &data->hctx->state))) {
+ blk_mq_put_tag(tags, data->ctx, tag + tag_offset);
+ return BLK_MQ_NO_TAG;
+ }
return tag + tag_offset;
}