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

[Ming Lei]

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@xxxxxxxxxx>
> Signed-off-by: Chen Jun <chenjun102@xxxxxxxxxx>

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

Thanks,
Ming