On 2019/09/29 22:50, Xiubo Li wrote: > On 2019/9/30 13:28, Damien Le Moal wrote: >> On 2019/09/29 18:52, [email protected] wrote: >>> From: Xiubo Li <[email protected]> >>> >>> 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 <[email protected]> >>> CC: Gabriel Krisman Bertazi <[email protected]> >>> Reviewed-by: Ming Lei <[email protected]> >>> --- >>> 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); >> You added the gfp_t argument to blk_mq_init_tags() but you are only using >> that >> argument with a hardcoded value here. So why not simply call kzalloc_node() >> in >> that function with the flags GFP_NOIO | __GFP_NOWARN | __GFP_NORETRY ? That >> would avoid needing to add the "gfp_t flags" argument and still fit with your >> patch 2 definition of BLK_MQ_GFP_FLAGS. > > The blk_mq_init_tags() is defined in another separate file, which I think it > means to provide a common way of initializing the tags stuff, and currently > in this path it needs GFP_NOIO while in others in future it may not.
blk_mq_alloc_rq_map() is currently the only user of blk_mq_init_tags(), so I do not see the point in doing this change now. If it is needed "in the future" then do it then. I do not mind the patch going in as is, but I really think that everything can be folded into your patch 2 without the addition of blk_mq_init_tags() additional argument. > > Thanks, > BRs > > >>> if (!tags) >>> return NULL; >>> >>> >> > > -- Damien Le Moal Western Digital Research
