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loop: Fix ABBA locking race

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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 no reason to hold q->limits_locks while getting
discord 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@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=a5d8c609c02f508672cc
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
OGAWA Hirofumi 2024-11-19 23:42:23 +09:00 committed by Jens Axboe
parent 46fd48ab3e
commit b49125574c
1 changed files with 15 additions and 15 deletions
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30
drivers/block/loop.c
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@ -770,12 +770,11 @@ static void loop_sysfs_exit(struct loop_device *lo)
&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;
/*
@ -788,24 +787,17 @@ static void loop_config_discard(struct loop_device *lo,
if (S_ISBLK(inode->i_mode)) {
struct block_device *bdev = I_BDEV(inode);
max_discard_sectors = bdev_write_zeroes_sectors(bdev);
granularity = bdev_discard_granularity(bdev);
*max_discard_sectors = bdev_write_zeroes_sectors(bdev);
*granularity = bdev_discard_granularity(bdev);
/*
* We use punch hole to reclaim the free space used by the
* 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 {
@ -991,6 +983,7 @@ static int loop_reconfigure_limits(struct loop_device *lo, unsigned int bsize)
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);
@ -1000,6 +993,8 @@ static int loop_reconfigure_limits(struct loop_device *lo, unsigned int bsize)
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;
@ -1009,7 +1004,12 @@ static int loop_reconfigure_limits(struct loop_device *lo, unsigned int bsize)
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);
}