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Message-ID: <CAFj5m9+FmQLLQkO7EUKnuuj+mpSUOY3EeUxSpXjJUvWtKfz26w@mail.gmail.com>
Date: Tue, 19 Nov 2024 20:10:46 +0800
From: Ming Lei <ming.lei@...hat.com>
To: OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
Cc: Jens Axboe <axboe@...nel.dk>, linux-block@...r.kernel.org,
syzbot <syzbot+a5d8c609c02f508672cc@...kaller.appspotmail.com>,
linkinjeon@...nel.org, linux-fsdevel@...r.kernel.org,
linux-kernel@...r.kernel.org, sj1557.seo@...sung.com,
syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [exfat?] possible deadlock in fat_count_free_clusters
On Tue, Nov 12, 2024 at 12:44 AM OGAWA Hirofumi
<hirofumi@...l.parknet.co.jp> wrote:
>
> Hi,
>
> syzbot <syzbot+a5d8c609c02f508672cc@...kaller.appspotmail.com> writes:
>
> > syzbot found the following issue on:
> >
> > HEAD commit: 929beafbe7ac Add linux-next specific files for 20241108
> > git tree: linux-next
> > console output: https://syzkaller.appspot.com/x/log.txt?x=1621bd87980000
> > kernel config: https://syzkaller.appspot.com/x/.config?x=75175323f2078363
> > dashboard link: https://syzkaller.appspot.com/bug?extid=a5d8c609c02f508672cc
> > compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
>
> This patch is to fix the above race. Please check this.
>
> Thanks
>
>
> From: OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
> Subject: [PATCH] loop: Fix ABBA locking race
> Date: Mon, 11 Nov 2024 21:53:36 +0900
>
> Current loop calls vfs_statfs() while holding the q->limits_lock. If
> FS takes some locking in vfs_statfs callback, this may lead to ABBA
> locking bug (at least, FAT fs has this issue actually).
>
> So this patch calls vfs_statfs() outside q->limits_locks instead,
> because looks like there is no reason to hold q->limits_locks while
> getting discard configs.
>
> Chain exists of:
> &sbi->fat_lock --> &q->q_usage_counter(io)#17 --> &q->limits_lock
>
> Possible unsafe locking scenario:
>
> CPU0 CPU1
> ---- ----
> lock(&q->limits_lock);
> lock(&q->q_usage_counter(io)#17);
> lock(&q->limits_lock);
> lock(&sbi->fat_lock);
>
> *** DEADLOCK ***
>
> Reported-by: syzbot+a5d8c609c02f508672cc@...kaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=a5d8c609c02f508672cc
> Signed-off-by: OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
> ---
> drivers/block/loop.c | 31 ++++++++++++++++---------------
> 1 file changed, 16 insertions(+), 15 deletions(-)
>
> diff --git a/drivers/block/loop.c b/drivers/block/loop.c
> index 78a7bb2..5f3ce51 100644
> --- a/drivers/block/loop.c 2024-09-16 13:45:20.253220178 +0900
> +++ b/drivers/block/loop.c 2024-11-11 21:51:00.910135443 +0900
> @@ -770,12 +770,11 @@ static void loop_sysfs_exit(struct loop_
> &loop_attribute_group);
> }
>
> -static void loop_config_discard(struct loop_device *lo,
> - struct queue_limits *lim)
> +static void loop_get_discard_config(struct loop_device *lo,
> + u32 *granularity, u32 *max_discard_sectors)
> {
> struct file *file = lo->lo_backing_file;
> struct inode *inode = file->f_mapping->host;
> - u32 granularity = 0, max_discard_sectors = 0;
> struct kstatfs sbuf;
>
> /*
> @@ -788,8 +787,9 @@ static void loop_config_discard(struct l
> if (S_ISBLK(inode->i_mode)) {
> struct request_queue *backingq = bdev_get_queue(I_BDEV(inode));
>
> - max_discard_sectors = backingq->limits.max_write_zeroes_sectors;
> - granularity = bdev_discard_granularity(I_BDEV(inode)) ?:
> + *max_discard_sectors =
> + backingq->limits.max_write_zeroes_sectors;
> + *granularity = bdev_discard_granularity(I_BDEV(inode)) ?:
> queue_physical_block_size(backingq);
>
> /*
> @@ -797,16 +797,9 @@ static void loop_config_discard(struct l
> * image a.k.a. discard.
> */
> } else if (file->f_op->fallocate && !vfs_statfs(&file->f_path, &sbuf)) {
> - max_discard_sectors = UINT_MAX >> 9;
> - granularity = sbuf.f_bsize;
> + *max_discard_sectors = UINT_MAX >> 9;
> + *granularity = sbuf.f_bsize;
> }
> -
> - lim->max_hw_discard_sectors = max_discard_sectors;
> - lim->max_write_zeroes_sectors = max_discard_sectors;
> - if (max_discard_sectors)
> - lim->discard_granularity = granularity;
> - else
> - lim->discard_granularity = 0;
> }
>
> struct loop_worker {
> @@ -992,6 +985,7 @@ static int loop_reconfigure_limits(struc
> struct inode *inode = file->f_mapping->host;
> struct block_device *backing_bdev = NULL;
> struct queue_limits lim;
> + u32 granularity = 0, max_discard_sectors = 0;
>
> if (S_ISBLK(inode->i_mode))
> backing_bdev = I_BDEV(inode);
> @@ -1001,6 +995,8 @@ static int loop_reconfigure_limits(struc
> if (!bsize)
> bsize = loop_default_blocksize(lo, backing_bdev);
>
> + loop_get_discard_config(lo, &granularity, &max_discard_sectors);
> +
> lim = queue_limits_start_update(lo->lo_queue);
> lim.logical_block_size = bsize;
> lim.physical_block_size = bsize;
> @@ -1010,7 +1006,12 @@ static int loop_reconfigure_limits(struc
> lim.features |= BLK_FEAT_WRITE_CACHE;
> if (backing_bdev && !bdev_nonrot(backing_bdev))
> lim.features |= BLK_FEAT_ROTATIONAL;
> - loop_config_discard(lo, &lim);
> + lim.max_hw_discard_sectors = max_discard_sectors;
> + lim.max_write_zeroes_sectors = max_discard_sectors;
> + if (max_discard_sectors)
> + lim.discard_granularity = granularity;
> + else
> + lim.discard_granularity = 0;
> return queue_limits_commit_update(lo->lo_queue, &lim);
> }
Looks fine,
Reviewed-by: Ming Lei <ming.lei@...hat.com>
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