Commit d8b90e63 authored by Baokun Li's avatar Baokun Li Committed by Theodore Ts'o
Browse files

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
8a83ac54 ("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: 8a83ac54 ("ext4: call bdev_getblk() from sb_getblk_gfp()")
Cc: stable@kernel.org
Signed-off-by: default avatarBaokun Li <libaokun1@huawei.com>
Reviewed-by: default avatarJan Kara <jack@suse.cz>
Signed-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
parent 981b696f

fs/ext4/ext4.h

+2 −0
Original line number Diff line number Diff line
@@ -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,

fs/ext4/indirect.c

+1 −1
Original line number Diff line number Diff line
@@ -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

fs/ext4/super.c

+9 −0
Original line number Diff line number Diff line
@@ -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,