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    Subject[PATCH 5.10 359/545] jbd2: fix outstanding credits assert in jbd2_journal_commit_transaction()
    Date
    From: Zhang Yi <yi.zhang@huawei.com>

    [ Upstream commit a89573ce4ad32f19f43ec669771726817e185be0 ]

    We catch an assert problem in jbd2_journal_commit_transaction() when
    doing fsstress and request falut injection tests. The problem is
    happened in a race condition between jbd2_journal_commit_transaction()
    and ext4_end_io_end(). Firstly, ext4_writepages() writeback dirty pages
    and start reserved handle, and then the journal was aborted due to some
    previous metadata IO error, jbd2_journal_abort() start to commit current
    running transaction, the committing procedure could be raced by
    ext4_end_io_end() and lead to subtract j_reserved_credits twice from
    commit_transaction->t_outstanding_credits, finally the
    t_outstanding_credits is mistakenly smaller than t_nr_buffers and
    trigger assert.

    kjournald2 kworker

    jbd2_journal_commit_transaction()
    write_unlock(&journal->j_state_lock);
    atomic_sub(j_reserved_credits, t_outstanding_credits); //sub once

    jbd2_journal_start_reserved()
    start_this_handle() //detect aborted journal
    jbd2_journal_free_reserved() //get running transaction
    read_lock(&journal->j_state_lock)
    __jbd2_journal_unreserve_handle()
    atomic_sub(j_reserved_credits, t_outstanding_credits);
    //sub again
    read_unlock(&journal->j_state_lock);

    journal->j_running_transaction = NULL;
    J_ASSERT(t_nr_buffers <= t_outstanding_credits) //bomb!!!

    Fix this issue by using journal->j_state_lock to protect the subtraction
    in jbd2_journal_commit_transaction().

    Fixes: 96f1e0974575 ("jbd2: avoid long hold times of j_state_lock while committing a transaction")
    Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
    Reviewed-by: Jan Kara <jack@suse.cz>
    Link: https://lore.kernel.org/r/20220611130426.2013258-1-yi.zhang@huawei.com
    Signed-off-by: Theodore Ts'o <tytso@mit.edu>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    fs/jbd2/commit.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c
    index 867362f45cf6..98cfa73cb165 100644
    --- a/fs/jbd2/commit.c
    +++ b/fs/jbd2/commit.c
    @@ -564,13 +564,13 @@ void jbd2_journal_commit_transaction(journal_t *journal)
    */
    jbd2_journal_switch_revoke_table(journal);

    + write_lock(&journal->j_state_lock);
    /*
    * Reserved credits cannot be claimed anymore, free them
    */
    atomic_sub(atomic_read(&journal->j_reserved_credits),
    &commit_transaction->t_outstanding_credits);

    - write_lock(&journal->j_state_lock);
    trace_jbd2_commit_flushing(journal, commit_transaction);
    stats.run.rs_flushing = jiffies;
    stats.run.rs_locked = jbd2_time_diff(stats.run.rs_locked,
    --
    2.35.1


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