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.chen@xxxxxxxxx> > --- > 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 <jack@xxxxxxxx> SUSE Labs, CR -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
