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    Subject[PATCH 5.13 194/351] ext4: fix WARN_ON_ONCE(!buffer_uptodate) after an error writing the superblock
    Date
    From: Ye Bin <yebin10@huawei.com>

    [ Upstream commit 558d6450c7755aa005d89021204b6cdcae5e848f ]

    If a writeback of the superblock fails with an I/O error, the buffer
    is marked not uptodate. However, this can cause a WARN_ON to trigger
    when we attempt to write superblock a second time. (Which might
    succeed this time, for cerrtain types of block devices such as iSCSI
    devices over a flaky network.)

    Try to detect this case in flush_stashed_error_work(), and also change
    __ext4_handle_dirty_metadata() so we always set the uptodate flag, not
    just in the nojournal case.

    Before this commit, this problem can be repliciated via:

    1. dmsetup create dust1 --table '0 2097152 dust /dev/sdc 0 4096'
    2. mount /dev/mapper/dust1 /home/test
    3. dmsetup message dust1 0 addbadblock 0 10
    4. cd /home/test
    5. echo "XXXXXXX" > t

    After a few seconds, we got following warning:

    [ 80.654487] end_buffer_async_write: bh=0xffff88842f18bdd0
    [ 80.656134] Buffer I/O error on dev dm-0, logical block 0, lost async page write
    [ 85.774450] EXT4-fs error (device dm-0): ext4_check_bdev_write_error:193: comm kworker/u16:8: Error while async write back metadata
    [ 91.415513] mark_buffer_dirty: bh=0xffff88842f18bdd0
    [ 91.417038] ------------[ cut here ]------------
    [ 91.418450] WARNING: CPU: 1 PID: 1944 at fs/buffer.c:1092 mark_buffer_dirty.cold+0x1c/0x5e
    [ 91.440322] Call Trace:
    [ 91.440652] __jbd2_journal_temp_unlink_buffer+0x135/0x220
    [ 91.441354] __jbd2_journal_unfile_buffer+0x24/0x90
    [ 91.441981] __jbd2_journal_refile_buffer+0x134/0x1d0
    [ 91.442628] jbd2_journal_commit_transaction+0x249a/0x3240
    [ 91.443336] ? put_prev_entity+0x2a/0x200
    [ 91.443856] ? kjournald2+0x12e/0x510
    [ 91.444324] kjournald2+0x12e/0x510
    [ 91.444773] ? woken_wake_function+0x30/0x30
    [ 91.445326] kthread+0x150/0x1b0
    [ 91.445739] ? commit_timeout+0x20/0x20
    [ 91.446258] ? kthread_flush_worker+0xb0/0xb0
    [ 91.446818] ret_from_fork+0x1f/0x30
    [ 91.447293] ---[ end trace 66f0b6bf3d1abade ]---

    Signed-off-by: Ye Bin <yebin10@huawei.com>
    Link: https://lore.kernel.org/r/20210615090537.3423231-1-yebin10@huawei.com
    Signed-off-by: Theodore Ts'o <tytso@mit.edu>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    fs/ext4/ext4_jbd2.c | 2 +-
    fs/ext4/super.c | 12 ++++++++++--
    2 files changed, 11 insertions(+), 3 deletions(-)

    diff --git a/fs/ext4/ext4_jbd2.c b/fs/ext4/ext4_jbd2.c
    index be799040a415..b96ecba91899 100644
    --- a/fs/ext4/ext4_jbd2.c
    +++ b/fs/ext4/ext4_jbd2.c
    @@ -327,6 +327,7 @@ int __ext4_handle_dirty_metadata(const char *where, unsigned int line,

    set_buffer_meta(bh);
    set_buffer_prio(bh);
    + set_buffer_uptodate(bh);
    if (ext4_handle_valid(handle)) {
    err = jbd2_journal_dirty_metadata(handle, bh);
    /* Errors can only happen due to aborted journal or a nasty bug */
    @@ -355,7 +356,6 @@ int __ext4_handle_dirty_metadata(const char *where, unsigned int line,
    err);
    }
    } else {
    - set_buffer_uptodate(bh);
    if (inode)
    mark_buffer_dirty_inode(bh, inode);
    else
    diff --git a/fs/ext4/super.c b/fs/ext4/super.c
    index 09f1f02e1d6d..6a4e040ea9b3 100644
    --- a/fs/ext4/super.c
    +++ b/fs/ext4/super.c
    @@ -705,15 +705,23 @@ static void flush_stashed_error_work(struct work_struct *work)
    * ext4 error handling code during handling of previous errors.
    */
    if (!sb_rdonly(sbi->s_sb) && journal) {
    + struct buffer_head *sbh = sbi->s_sbh;
    handle = jbd2_journal_start(journal, 1);
    if (IS_ERR(handle))
    goto write_directly;
    - if (jbd2_journal_get_write_access(handle, sbi->s_sbh)) {
    + if (jbd2_journal_get_write_access(handle, sbh)) {
    jbd2_journal_stop(handle);
    goto write_directly;
    }
    ext4_update_super(sbi->s_sb);
    - if (jbd2_journal_dirty_metadata(handle, sbi->s_sbh)) {
    + if (buffer_write_io_error(sbh) || !buffer_uptodate(sbh)) {
    + ext4_msg(sbi->s_sb, KERN_ERR, "previous I/O error to "
    + "superblock detected");
    + clear_buffer_write_io_error(sbh);
    + set_buffer_uptodate(sbh);
    + }
    +
    + if (jbd2_journal_dirty_metadata(handle, sbh)) {
    jbd2_journal_stop(handle);
    goto write_directly;
    }
    --
    2.30.2


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