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ext4: add ext4_sb_bread_nofail() helper function for ext4_free_branches() 

The implicit __GFP_NOFAIL flag in ext4_sb_bread() was removed in commit
8a83ac5494 ("ext4: call bdev_getblk() from sb_getblk_gfp()"), meaning
the function can now fail under memory pressure.

Most callers of ext4_sb_bread() propagate the error to userspace and do not
remount the filesystem read-only. However, ext4_free_branches() handles
ext4_sb_bread() failure by remounting the filesystem read-only.

This implies that an ext3 filesystem (mounted via the ext4 driver) could be
forcibly remounted read-only due to a transient page allocation failure,
which is unacceptable.

To mitigate this, introduce a new helper function, ext4_sb_bread_nofail(),
which explicitly uses __GFP_NOFAIL, and use it in ext4_free_branches().

Fixes: 8a83ac5494 ("ext4: call bdev_getblk() from sb_getblk_gfp()")
Cc: stable@kernel.org
Signed-off-by: Baokun Li <libaokun1@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
This commit is contained in:
Baokun Li 2025-08-21 21:38:57 +08:00 committed by Theodore Ts'o
parent 981b696faf
commit d8b90e6387
3 changed files with 12 additions and 1 deletions
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2
fs/ext4/ext4.h
View File

@ -3134,6 +3134,8 @@ extern struct buffer_head *ext4_sb_bread(struct super_block *sb,
sector_t block, blk_opf_t op_flags);
extern struct buffer_head *ext4_sb_bread_unmovable(struct super_block *sb,
sector_t block);
extern struct buffer_head *ext4_sb_bread_nofail(struct super_block *sb,
sector_t block);
extern void ext4_read_bh_nowait(struct buffer_head *bh, blk_opf_t op_flags,
bh_end_io_t *end_io, bool simu_fail);
extern int ext4_read_bh(struct buffer_head *bh, blk_opf_t op_flags,

2
fs/ext4/indirect.c
View File

@ -1025,7 +1025,7 @@ static void ext4_free_branches(handle_t *handle, struct inode *inode,
}
/* Go read the buffer for the next level down */
bh = ext4_sb_bread(inode->i_sb, nr, 0);
bh = ext4_sb_bread_nofail(inode->i_sb, nr);
/*
* A read failure? Report error and clear slot

9
fs/ext4/super.c
View File

@ -265,6 +265,15 @@ struct buffer_head *ext4_sb_bread_unmovable(struct super_block *sb,
return __ext4_sb_bread_gfp(sb, block, 0, gfp);
}
struct buffer_head *ext4_sb_bread_nofail(struct super_block *sb,
sector_t block)
{
gfp_t gfp = mapping_gfp_constraint(sb->s_bdev->bd_mapping,
~__GFP_FS) | __GFP_MOVABLE | __GFP_NOFAIL;
return __ext4_sb_bread_gfp(sb, block, 0, gfp);
}
void ext4_sb_breadahead_unmovable(struct super_block *sb, sector_t block)
{
struct buffer_head *bh = bdev_getblk(sb->s_bdev, block,