On Wed 27-09-17 15:15:08, Zumeng Chen wrote:
> It seems kfree(new_congested) does nothing since new_congested has already
> been set null pointer before kfree, so remove it.
>
> Meanwhile kmemleak reports the following memory leakage:
>
> unreferenced object 0xcadbb440 (size 64):
> comm "kworker/0:4", pid 1399, jiffies 4294946504 (age 808.290s)
> hex dump (first 32 bytes):
> 00 00 00 00 01 00 00 00 00 00 00 00 01 00 00 00 ................
> 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
> backtrace:
> [<c028fb64>] kmem_cache_alloc_trace+0x2c4/0x3cc
> [<c025fe70>] wb_congested_get_create+0x9c/0x140
> [<c0260100>] wb_init+0x184/0x1f4
> [<c02601fc>] bdi_init+0x8c/0xd4
> [<c051f75c>] blk_alloc_queue_node+0x9c/0x2d8
> [<c05227e8>] blk_init_queue_node+0x2c/0x64
> [<c052283c>] blk_init_queue+0x1c/0x20
> [<c06c7b30>] __scsi_alloc_queue+0x28/0x44
> [<c06caf4c>] scsi_alloc_queue+0x24/0x80
> [<c06cc0b8>] scsi_alloc_sdev+0x21c/0x34c
> [<c06ccc00>] scsi_probe_and_add_lun+0x878/0xb04
> [<c06cd114>] __scsi_scan_target+0x288/0x59c
> [<c06cd4b0>] scsi_scan_channel+0x88/0x9c
> [<c06cd9b8>] scsi_scan_host_selected+0x118/0x130
> [<c06cda70>] do_scsi_scan_host+0xa0/0xa4
> [<c06cdbe4>] scsi_scan_host+0x170/0x1b4
>
> wb_congested allocates memory for congested when wb_congested_get_create,
> and release it when exit or failure by wb_congested_put.
>
The patch is just wrong. Think what will happen if we decide to allocate
new_congested but then loose a race with somebody creating the same congested
structure (so we find it in the rb-tree).
Honza
> Signed-off-by: Zumeng Chen <zumeng.c...@gmail.com>
> ---
> mm/backing-dev.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/backing-dev.c b/mm/backing-dev.c
> index e19606b..d816b2a 100644
> --- a/mm/backing-dev.c
> +++ b/mm/backing-dev.c
> @@ -457,6 +457,7 @@ wb_congested_get_create(struct backing_dev_info *bdi, int
> blkcg_id, gfp_t gfp)
>
> /* allocate storage for new one and retry */
> new_congested = kzalloc(sizeof(*new_congested), gfp);
> + kmemleak_ignore(new_congested);
> if (!new_congested)
> return NULL;
>
> @@ -468,7 +469,6 @@ wb_congested_get_create(struct backing_dev_info *bdi, int
> blkcg_id, gfp_t gfp)
> found:
> atomic_inc(&congested->refcnt);
> spin_unlock_irqrestore(&cgwb_lock, flags);
> - kfree(new_congested);
> return congested;
> }
>
> --
> 2.7.4
>
--
Jan Kara <j...@suse.com>
SUSE Labs, CR
