From: Takashi Iwai Date: Wed, 10 Dec 2014 16:38:30 +0100 Subject: [PATCH] blk-mq: Fix uninitialized kobject at CPU hotplugging When a CPU is hotplugged, the current blk-mq spews a warning like: kobject '(null)' (ffffe8ffffc8b5d8): tried to add an uninitialized object, something is seriously wrong. CPU: 1 PID: 1386 Comm: systemd-udevd Not tainted 3.18.0-rc7-2.g088d59b-default #1 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.7.5-20140531_171129-lamiak 04/01/2014 0000000000000000 0000000000000002 ffffffff81605f07 ffffe8ffffc8b5d8 ffffffff8132c7a0 ffff88023341d370 0000000000000020 ffff8800bb05bd58 ffff8800bb05bd08 000000000000a0a0 000000003f441940 0000000000000007 Call Trace: [] dump_trace+0x86/0x330 [] show_stack_log_lvl+0x94/0x170 [] show_stack+0x21/0x50 [] dump_stack+0x41/0x51 [] kobject_add+0xa0/0xb0 [] blk_mq_register_hctx+0x91/0xb0 [] blk_mq_sysfs_register+0x3e/0x60 [] blk_mq_queue_reinit_notify+0xf8/0x190 [] notifier_call_chain+0x4c/0x70 [] cpu_notify+0x23/0x50 [] _cpu_up+0x157/0x170 [] cpu_up+0x89/0xb0 [] cpu_subsys_online+0x35/0x80 [] device_online+0x5d/0xa0 [] online_store+0x75/0x80 [] kernfs_fop_write+0xda/0x150 [] vfs_write+0xb2/0x1f0 [] SyS_write+0x42/0xb0 [] system_call_fastpath+0x16/0x1b [<00007f0132fb24e0>] 0x7f0132fb24e0 This is indeed because of an uninitialized kobject for blk_mq_ctx. The blk_mq_ctx kobjects are initialized in blk_mq_sysfs_init(), but it goes loop over hctx_for_each_ctx(), i.e. it initializes only for online CPUs. Thus, when a CPU is hotplugged, the ctx for the newly onlined CPU is registered without initialization. This patch fixes the issue by initializing the all ctx kobjects belonging to each queue. Bugzilla: https://bugzilla.novell.com/show_bug.cgi?id=908794 Cc: Signed-off-by: Takashi Iwai Signed-off-by: Jens Axboe --- block/blk-mq-sysfs.c | 9 ++++----- 1 file changed, 4 insertions(+), 5 deletions(-) diff --git a/block/blk-mq-sysfs.c b/block/blk-mq-sysfs.c index ed5217867555..e0fb3f4a628f 100644 --- a/block/blk-mq-sysfs.c +++ b/block/blk-mq-sysfs.c @@ -390,16 +390,15 @@ static void blk_mq_sysfs_init(struct request_queue *q) { struct blk_mq_hw_ctx *hctx; struct blk_mq_ctx *ctx; - int i, j; + int i; kobject_init(&q->mq_kobj, &blk_mq_ktype); - queue_for_each_hw_ctx(q, hctx, i) { + queue_for_each_hw_ctx(q, hctx, i) kobject_init(&hctx->kobj, &blk_mq_hw_ktype); - hctx_for_each_ctx(hctx, ctx, j) - kobject_init(&ctx->kobj, &blk_mq_ctx_ktype); - } + queue_for_each_ctx(q, ctx, i) + kobject_init(&ctx->kobj, &blk_mq_ctx_ktype); } int blk_mq_register_disk(struct gendisk *disk) -- 2.1.0