From: Baokun Li <libaokun1@xxxxxxxxxx>
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 <libaokun1@xxxxxxxxxx>
---
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
