From: Sebastian Andrzej Siewior Date: Wed, 9 Apr 2014 10:37:23 +0200 Subject: block: mq: use cpu_light() Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.4/patches-4.4.1-rt5.tar.xz there is a might sleep splat because get_cpu() disables preemption and later we grab a lock. As a workaround for this we use get_cpu_light() and an additional lock to prevent taking the same ctx. There is a lock member in the ctx already but there some functions which do ++ on the member and this works with irq off but on RT we would need the extra lock. Signed-off-by: Sebastian Andrzej Siewior --- block/blk-mq.c | 4 ++++ block/blk-mq.h | 17 ++++++++++++++--- 2 files changed, 18 insertions(+), 3 deletions(-) --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -1385,7 +1385,9 @@ static blk_qc_t blk_sq_make_request(stru blk_mq_put_ctx(data.ctx); 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); } @@ -1587,6 +1589,7 @@ static int blk_mq_hctx_cpu_offline(struc blk_mq_hctx_clear_pending(hctx, ctx); } spin_unlock(&ctx->lock); + __blk_mq_put_ctx(ctx); if (list_empty(&tmp)) return NOTIFY_OK; @@ -1780,6 +1783,7 @@ static void blk_mq_init_cpu_queues(struc 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; --- a/block/blk-mq.h +++ b/block/blk-mq.h @@ -9,6 +9,7 @@ struct blk_mq_ctx { struct list_head rq_list; } ____cacheline_aligned_in_smp; + spinlock_t cpu_lock; unsigned int cpu; unsigned int index_hw; @@ -74,7 +75,11 @@ struct blk_align_bitmap { static inline struct blk_mq_ctx *__blk_mq_get_ctx(struct request_queue *q, unsigned int cpu) { - return per_cpu_ptr(q->queue_ctx, cpu); + struct blk_mq_ctx *ctx; + + ctx = per_cpu_ptr(q->queue_ctx, cpu); + spin_lock(&ctx->cpu_lock); + return ctx; } /* @@ -85,12 +90,18 @@ static inline struct blk_mq_ctx *__blk_m */ static inline struct blk_mq_ctx *blk_mq_get_ctx(struct request_queue *q) { - return __blk_mq_get_ctx(q, get_cpu()); + 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) { - put_cpu(); + __blk_mq_put_ctx(ctx); + put_cpu_light(); } struct blk_mq_alloc_data {