Re: [PATCH 1/2] md/raid5: Remove unnecessary bio_put() in raid5_read_one_chunk()

Guoqing Jiang
2022-09-06T06:04:38Z

On 9/3/22 1:16 AM, Logan Gunthorpe wrote:
> From: David Sloan <david.sloan@eideticom.com>
>
> When running chunk-sized reads on disks with badblocks duplicate bio
> free/puts are observed:
>
> =============================================================================
> BUG bio-200 (Not tainted): Object already free
> -----------------------------------------------------------------------------
> Allocated in mempool_alloc_slab+0x17/0x20 age=3 cpu=2 pid=7504
> __slab_alloc.constprop.0+0x5a/0xb0
> kmem_cache_alloc+0x31e/0x330
> mempool_alloc_slab+0x17/0x20
> mempool_alloc+0x100/0x2b0
> bio_alloc_bioset+0x181/0x460
> do_mpage_readpage+0x776/0xd00
> mpage_readahead+0x166/0x320
> blkdev_readahead+0x15/0x20
> read_pages+0x13f/0x5f0
> page_cache_ra_unbounded+0x18d/0x220
> force_page_cache_ra+0x181/0x1c0
> page_cache_sync_ra+0x65/0xb0
> filemap_get_pages+0x1df/0xaf0
> filemap_read+0x1e1/0x700
> blkdev_read_iter+0x1e5/0x330
> vfs_read+0x42a/0x570
> Freed in mempool_free_slab+0x17/0x20 age=3 cpu=2 pid=7504
> kmem_cache_free+0x46d/0x490
> mempool_free_slab+0x17/0x20
> mempool_free+0x66/0x190
> bio_free+0x78/0x90
> bio_put+0x100/0x1a0
> raid5_make_request+0x2259/0x2450
> md_handle_request+0x402/0x600
> md_submit_bio+0xd9/0x120
> __submit_bio+0x11f/0x1b0
> submit_bio_noacct_nocheck+0x204/0x480
> submit_bio_noacct+0x32e/0xc70
> submit_bio+0x98/0x1a0
> mpage_readahead+0x250/0x320
> blkdev_readahead+0x15/0x20
> read_pages+0x13f/0x5f0
> page_cache_ra_unbounded+0x18d/0x220
> Slab 0xffffea000481b600 objects=21 used=0 fp=0xffff8881206d8940 flags=0x17ffffc0010201(locked|slab|head|node=0|zone=2|lastcpupid=0x1fffff)
> CPU: 0 PID: 34525 Comm: kworker/u24:2 Not tainted 6.0.0-rc2-localyes-265166-gf11c5343fa3f #143
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.13.0-1ubuntu1.1 04/01/2014
> Workqueue: raid5wq raid5_do_work
> Call Trace:
> <TASK>
> dump_stack_lvl+0x5a/0x78
> dump_stack+0x10/0x16
> print_trailer+0x158/0x165
> object_err+0x35/0x50
> free_debug_processing.cold+0xb7/0xbe
> __slab_free+0x1ae/0x330
> kmem_cache_free+0x46d/0x490
> mempool_free_slab+0x17/0x20
> mempool_free+0x66/0x190
> bio_free+0x78/0x90
> bio_put+0x100/0x1a0
> mpage_end_io+0x36/0x150
> bio_endio+0x2fd/0x360
> md_end_io_acct+0x7e/0x90
> bio_endio+0x2fd/0x360
> handle_failed_stripe+0x960/0xb80
> handle_stripe+0x1348/0x3760
> handle_active_stripes.constprop.0+0x72a/0xaf0
> raid5_do_work+0x177/0x330
> process_one_work+0x616/0xb20
> worker_thread+0x2bd/0x6f0
> kthread+0x179/0x1b0
> ret_from_fork+0x22/0x30
> </TASK>
>
> The double free is caused by an unnecessary bio_put() in the
> if(is_badblock(...)) error path in raid5_read_one_chunk().
>
> The error path was moved ahead of bio_alloc_clone() in c82aa1b76787c
> ("md/raid5: move checking badblock before clone bio in
> raid5_read_one_chunk"). The previous code checked and freed align_bio
> which required a bio_put. After he move that is no longer needed as
> raid_bio is returned to the control of the common io path which
> performs its own endio resulting in a double free on bad device blocks.
>
> Fixes: c82aa1b76787c ("md/raid5: move checking badblock before clone bio in raid5_read_one_chunk")
> Signed-off-by: David Sloan <david.sloan@eideticom.com>
> [logang@deltatee.com: minor rewording of commit message]
> Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
> ---
> drivers/md/raid5.c | 1 -
> 1 file changed, 1 deletion(-)
>
> diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
> index 4e6d865a6456..734f92e75f85 100644
> --- a/drivers/md/raid5.c
> +++ b/drivers/md/raid5.c
> @@ -5538,7 +5538,6 @@ static int raid5_read_one_chunk(struct mddev *mddev, struct bio *raid_bio)
>
> if (is_badblock(rdev, sector, bio_sectors(raid_bio), &first_bad,
> &bad_sectors)) {
> - bio_put(raid_bio);
> rdev_dec_pending(rdev, mddev);
> return 0;
> }

Acked-by: Guoqing Jiang <Guoqing.jiang@linux.dev>

Thanks,
Guoqing