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Date: Fri, 27 May 2022 17:16:42 +0800 From: yebin <yebin10@...wei.com> To: Jan Kara <jack@...e.cz>, Ritesh Harjani <ritesh.list@...il.com> CC: <tytso@....edu>, <adilger.kernel@...ger.ca>, <linux-ext4@...r.kernel.org>, <linux-kernel@...r.kernel.org> Subject: Re: [PATCH -next] ext4: fix super block checksum incorrect after mount On 2022/5/25 19:54, Jan Kara wrote: > On Wed 25-05-22 13:21:23, Ritesh Harjani wrote: >> On 22/05/25 09:29AM, Ye Bin wrote: >>> We got issue as follows: >>> [home]# mount /dev/sda test >>> EXT4-fs (sda): warning: mounting fs with errors, running e2fsck is recommended >>> [home]# dmesg >>> EXT4-fs (sda): warning: mounting fs with errors, running e2fsck is recommended >>> EXT4-fs (sda): Errors on filesystem, clearing orphan list. >>> EXT4-fs (sda): recovery complete >>> EXT4-fs (sda): mounted filesystem with ordered data mode. Quota mode: none. >>> [home]# debugfs /dev/sda >>> debugfs 1.46.5 (30-Dec-2021) >>> Checksum errors in superblock! Retrying... >>> >>> Reason is ext4_orphan_cleanup will reset ‘s_last_orphan’ but not update >>> super block checksum. >>> To solve above issue, defer update super block checksum after ext4_orphan_cleanup. >> I agree with the analysis. However after [1], I think all updates to superblock >> (including checksum computation) should be done within buffer lock. >> (lock_buffer(), unlock_buffer()). >> >> [1]: https://lore.kernel.org/all/20201216101844.22917-4-jack@suse.cz/ > So technically you're right that we should hold buffer lock all the time > from before we modify superblock buffer until we recompute the checksum (so > that we avoid writing superblock with mismatched checksum). To do this we'd > have to put checksum recomputations and superblock buffer locking into > ext4_orphan_cleanup() around setting of es->s_last_orphan (in three places > there AFAICS). A bit tedious but it would actually also fix a (theoretical) > race that someone decides to write out superblock after we set > s_last_orphan but before we set the checksum. > > Overall I'm not convinced this is really necessary so I'd be OK even with > what Ye suggested. That is IMHO better than mostly pointless locking just > around checksum computation because that just makes reader wonder why is it > needed... > > Honza Thanks for your reply. Does my patch need to be adjusted? >> With lock changes added, feel free to add - >> >> Reviewed-by: Ritesh Harjani <ritesh.list@...il.com> >> >> >>> >>> Signed-off-by: Ye Bin <yebin10@...wei.com> >>> --- >>> fs/ext4/super.c | 16 ++++++++-------- >>> 1 file changed, 8 insertions(+), 8 deletions(-) >>> >>> diff --git a/fs/ext4/super.c b/fs/ext4/super.c >>> index f9a3ad683b4a..c47204029429 100644 >>> --- a/fs/ext4/super.c >>> +++ b/fs/ext4/super.c >>> @@ -5300,14 +5300,6 @@ static int __ext4_fill_super(struct fs_context *fc, struct super_block *sb) >>> err = percpu_counter_init(&sbi->s_freeinodes_counter, freei, >>> GFP_KERNEL); >>> } >>> - /* >>> - * Update the checksum after updating free space/inode >>> - * counters. Otherwise the superblock can have an incorrect >>> - * checksum in the buffer cache until it is written out and >>> - * e2fsprogs programs trying to open a file system immediately >>> - * after it is mounted can fail. >>> - */ >>> - ext4_superblock_csum_set(sb); >>> if (!err) >>> err = percpu_counter_init(&sbi->s_dirs_counter, >>> ext4_count_dirs(sb), GFP_KERNEL); >>> @@ -5365,6 +5357,14 @@ static int __ext4_fill_super(struct fs_context *fc, struct super_block *sb) >>> EXT4_SB(sb)->s_mount_state |= EXT4_ORPHAN_FS; >>> ext4_orphan_cleanup(sb, es); >>> EXT4_SB(sb)->s_mount_state &= ~EXT4_ORPHAN_FS; >>> + /* >>> + * Update the checksum after updating free space/inode counters and >>> + * ext4_orphan_cleanup. Otherwise the superblock can have an incorrect >>> + * checksum in the buffer cache until it is written out and >>> + * e2fsprogs programs trying to open a file system immediately >>> + * after it is mounted can fail. >>> + */ >>> + ext4_superblock_csum_set(sb); >>> if (needs_recovery) { >>> ext4_msg(sb, KERN_INFO, "recovery complete"); >>> err = ext4_mark_recovery_complete(sb, es); >>> -- >>> 2.31.1 >>>
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