Re: [PATCH] blk-mq: Fix kmemleak in blk_mq_init_allocated_queue

Ming Lei
2022-10-31T14:09:08Z

On Mon, Oct 31, 2022 at 03:12:42AM +0000, Chen Jun wrote:
> There is a kmemleak caused by modprobe null_blk.ko
>
> unreferenced object 0xffff8881acb1f000 (size 1024):
> comm "modprobe", pid 836, jiffies 4294971190 (age 27.068s)
> hex dump (first 32 bytes):
> 00 00 00 00 ad 4e ad de ff ff ff ff 00 00 00 00 .....N..........
> ff ff ff ff ff ff ff ff 00 53 99 9e ff ff ff ff .........S......
> backtrace:
> [<000000004a10c249>] kmalloc_node_trace+0x22/0x60
> [<00000000648f7950>] blk_mq_alloc_and_init_hctx+0x289/0x350
> [<00000000af06de0e>] blk_mq_realloc_hw_ctxs+0x2fe/0x3d0
> [<00000000e00c1872>] blk_mq_init_allocated_queue+0x48c/0x1440
> [<00000000d16b4e68>] __blk_mq_alloc_disk+0xc8/0x1c0
> [<00000000d10c98c3>] 0xffffffffc450d69d
> [<00000000b9299f48>] 0xffffffffc4538392
> [<0000000061c39ed6>] do_one_initcall+0xd0/0x4f0
> [<00000000b389383b>] do_init_module+0x1a4/0x680
> [<0000000087cf3542>] load_module+0x6249/0x7110
> [<00000000beba61b8>] __do_sys_finit_module+0x140/0x200
> [<00000000fdcfff51>] do_syscall_64+0x35/0x80
> [<000000003c0f1f71>] entry_SYSCALL_64_after_hwframe+0x46/0xb0
>
> That is because q->ma_ops is set to NULL before blk_release_queue is
> called.
>
> blk_mq_init_queue_data
> blk_mq_init_allocated_queue
> blk_mq_realloc_hw_ctxs
> for (i = 0; i < set->nr_hw_queues; i++) {
> old_hctx = xa_load(&q->hctx_table, i);
> if (!blk_mq_alloc_and_init_hctx(.., i, ..)) [1]
> if (!old_hctx)
> break;
>
> xa_for_each_start(&q->hctx_table, j, hctx, j)
> blk_mq_exit_hctx(q, set, hctx, j); [2]
>
> if (!q->nr_hw_queues) [3]
> goto err_hctxs;
>
> err_exit:
> q->mq_ops = NULL; [4]
>
> blk_put_queue
> blk_release_queue
> if (queue_is_mq(q)) [5]
> blk_mq_release(q);
>
> [1]: blk_mq_alloc_and_init_hctx failed at i != 0.
> [2]: The hctxs allocated by [1] are moved to q->unused_hctx_list and
> will be cleaned up in blk_mq_release.
> [3]: q->nr_hw_queues is 0.
> [4]: Set q->mq_ops to NULL.
> [5]: queue_is_mq returns false due to [4]. And blk_mq_release
> will not be called. The hctxs in q->unused_hctx_list are leaked.
>
> To fix it, call blk_release_queue in exception path.
>
> Fixes: 2f8f1336a48b ("blk-mq: always free hctx after request queue is freed")
> Signed-off-by: Yuan Can <yuancan@huawei.com>
> Signed-off-by: Chen Jun <chenjun102@huawei.com>

Reviewed-by: Ming Lei <ming.lei@redhat.com>

Thanks,
Ming