From: Baokun Li The implicit __GFP_NOFAIL flag in ext4_sb_bread() was removed in commit 8a83ac54940d ("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: 8a83ac54940d ("ext4: call bdev_getblk() from sb_getblk_gfp()") Signed-off-by: Baokun Li --- fs/ext4/ext4.h | 2 ++ fs/ext4/indirect.c | 2 +- fs/ext4/super.c | 9 +++++++++ 3 files changed, 12 insertions(+), 1 deletion(-) diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h index 106484739932..32315e51639e 100644 --- a/fs/ext4/ext4.h +++ b/fs/ext4/ext4.h @@ -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, diff --git a/fs/ext4/indirect.c b/fs/ext4/indirect.c index 7de327fa7b1c..39350a18e919 100644 --- a/fs/ext4/indirect.c +++ b/fs/ext4/indirect.c @@ -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 diff --git a/fs/ext4/super.c b/fs/ext4/super.c index c7d39da7e733..a0e2b396aa76 100644 --- a/fs/ext4/super.c +++ b/fs/ext4/super.c @@ -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, -- 2.39.2