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@xxxxxxxxxx>
Signed-off-by: Jan Kara <jack@xxxxxxx>
---
fs/jbd2/transaction.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
index dd89ad2..8cdf489 100644
--- a/fs/jbd2/transaction.c
+++ b/fs/jbd2/transaction.c
@@ -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);
--
1.8.1.4
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