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jbd2: fix race in t_outstanding_credits update in jbd2_journal_extend()

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jbd2_journal_extend() first checked whether transaction can accept
extending handle with more credits and then added credits to
t_outstanding_credits.  This can race with start_this_handle() adding
another handle to a transaction and thus overbooking a transaction.
Make jbd2_journal_extend() use atomic_add_return() to close the race.

Reviewed-by: Zheng Liu <wenqing.lz@taobao.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
This commit is contained in:
Jan Kara 2013-06-04 12:22:15 -04:00 committed by Theodore Ts'o
parent 76c3990456
commit fe1e8db598
1 changed files with 4 additions and 2 deletions
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6
fs/jbd2/transaction.c
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@ -433,11 +433,13 @@ int jbd2_journal_extend(handle_t *handle, int nblocks)
}
spin_lock(&transaction->t_handle_lock);
wanted = atomic_read(&transaction->t_outstanding_credits) + nblocks;
wanted = atomic_add_return(nblocks,
&transaction->t_outstanding_credits);
if (wanted > journal->j_max_transaction_buffers) {
jbd_debug(3, "denied handle %p %d blocks: "
"transaction too large\n", handle, nblocks);
atomic_sub(nblocks, &transaction->t_outstanding_credits);
goto unlock;
}
@ -445,6 +447,7 @@ int jbd2_journal_extend(handle_t *handle, int nblocks)
jbd2_log_space_left(journal)) {
jbd_debug(3, "denied handle %p %d blocks: "
"insufficient log space\n", handle, nblocks);
atomic_sub(nblocks, &transaction->t_outstanding_credits);
goto unlock;
}
@ -456,7 +459,6 @@ int jbd2_journal_extend(handle_t *handle, int nblocks)
handle->h_buffer_credits += nblocks;
handle->h_requested_credits += nblocks;
atomic_add(nblocks, &transaction->t_outstanding_credits);
result = 0;
jbd_debug(3, "extended handle %p by %d\n", handle, nblocks);