On Sun, Sep 15, 2019 at 05:56:56PM +0530, xiubli@xxxxxxxxxx wrote:
> From: Xiubo Li <xiubli@xxxxxxxxxx>
>
> For some storage drivers, such as the nbd, when there has new socket
> connections added, it will update the hardware queue number by calling
> blk_mq_update_nr_hw_queues(), in which it will freeze all the queues
> first. And then tries to do the hardware queue updating stuff.
>
> But int blk_mq_alloc_rq_map()-->blk_mq_init_tags(), when allocating
> memory for tags, it may cause the mm do the memories direct reclaiming,
> since the queues has been freezed, so if needs to flush the page cache
> to disk, it will stuck in generic_make_request()-->blk_queue_enter() by
> waiting the queues to be unfreezed and then cause deadlock here.
>
> Since the memory size requested here is a small one, which will make
> it not that easy to happen with a large size, but in theory this could
> happen when the OS is running in pressure and out of memory.
>
> Gabriel Krisman Bertazi has hit the similar issue by fixing it in
> commit 36e1f3d10786 ("blk-mq: Avoid memory reclaim when remapping
> queues"), but might forget this part.
>
> Signed-off-by: Xiubo Li <xiubli@xxxxxxxxxx>
> CC: Gabriel Krisman Bertazi <krisman@xxxxxxxxxxxxxxxxxx>
> ---
> block/blk-mq-tag.c | 5 +++--
> block/blk-mq-tag.h | 5 ++++-
> block/blk-mq.c | 3 ++-
> 3 files changed, 9 insertions(+), 4 deletions(-)
>
> diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
> index 008388e82b5c..04ee0e4c3fa1 100644
> --- a/block/blk-mq-tag.c
> +++ b/block/blk-mq-tag.c
> @@ -462,7 +462,8 @@ static struct blk_mq_tags *blk_mq_init_bitmap_tags(struct blk_mq_tags *tags,
>
> struct blk_mq_tags *blk_mq_init_tags(unsigned int total_tags,
> unsigned int reserved_tags,
> - int node, int alloc_policy)
> + int node, int alloc_policy,
> + gfp_t flags)
> {
> struct blk_mq_tags *tags;
>
> @@ -471,7 +472,7 @@ struct blk_mq_tags *blk_mq_init_tags(unsigned int total_tags,
> return NULL;
> }
>
> - tags = kzalloc_node(sizeof(*tags), GFP_KERNEL, node);
> + tags = kzalloc_node(sizeof(*tags), flags, node);
> if (!tags)
> return NULL;
>
> diff --git a/block/blk-mq-tag.h b/block/blk-mq-tag.h
> index 61deab0b5a5a..296e0bc97126 100644
> --- a/block/blk-mq-tag.h
> +++ b/block/blk-mq-tag.h
> @@ -22,7 +22,10 @@ struct blk_mq_tags {
> };
>
>
> -extern struct blk_mq_tags *blk_mq_init_tags(unsigned int nr_tags, unsigned int reserved_tags, int node, int alloc_policy);
> +extern struct blk_mq_tags *blk_mq_init_tags(unsigned int nr_tags,
> + unsigned int reserved_tags,
> + int node, int alloc_policy,
> + gfp_t flags);
> extern void blk_mq_free_tags(struct blk_mq_tags *tags);
>
> extern unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data);
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index 240416057f28..9c52e4dfe132 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -2090,7 +2090,8 @@ struct blk_mq_tags *blk_mq_alloc_rq_map(struct blk_mq_tag_set *set,
> node = set->numa_node;
>
> tags = blk_mq_init_tags(nr_tags, reserved_tags, node,
> - BLK_MQ_FLAG_TO_ALLOC_POLICY(set->flags));
> + BLK_MQ_FLAG_TO_ALLOC_POLICY(set->flags),
> + GFP_NOIO | __GFP_NOWARN | __GFP_NORETRY);
Now, there are three uses on 'GFP_NOIO | __GFP_NOWARN | __GFP_NORETRY',
and code gets cleaner if you make it as one const variable in
blk_mq_alloc_rq_map.
Otherwise, looks fine:
Reviewed-by: Ming Lei <ming.lei@xxxxxxxxxx>
thanks,
Ming
