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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>
a89573ce4a