The patch below does not apply to the 5.4-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From 14ff6286309e2853aed50083c9a83328423fdd8c Mon Sep 17 00:00:00 2001
From: Jan Kara jack@suse.cz Date: Wed, 20 May 2020 15:31:19 +0200 Subject: [PATCH] jbd2: avoid leaking transaction credits when unreserving handle
When reserved transaction handle is unused, we subtract its reserved credits in __jbd2_journal_unreserve_handle() called from jbd2_journal_stop(). However this function forgets to remove reserved credits from transaction->t_outstanding_credits and thus the transaction space that was reserved remains effectively leaked. The leaked transaction space can be quite significant in some cases and leads to unnecessarily small transactions and thus reducing throughput of the journalling machinery. E.g. fsmark workload creating lots of 4k files was observed to have about 20% lower throughput due to this when ext4 is mounted with dioread_nolock mount option.
Subtract reserved credits from t_outstanding_credits as well.
CC: stable@vger.kernel.org Fixes: 8f7d89f36829 ("jbd2: transaction reservation support") Reviewed-by: Andreas Dilger adilger@dilger.ca Signed-off-by: Jan Kara jack@suse.cz Link: https://lore.kernel.org/r/20200520133119.1383-3-jack@suse.cz Signed-off-by: Theodore Ts'o tytso@mit.edu
diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c index 3dccc23cf010..e91aad3637a2 100644 --- a/fs/jbd2/transaction.c +++ b/fs/jbd2/transaction.c @@ -541,17 +541,24 @@ handle_t *jbd2_journal_start(journal_t *journal, int nblocks) } EXPORT_SYMBOL(jbd2_journal_start);
-static void __jbd2_journal_unreserve_handle(handle_t *handle) +static void __jbd2_journal_unreserve_handle(handle_t *handle, transaction_t *t) { journal_t *journal = handle->h_journal;
WARN_ON(!handle->h_reserved); sub_reserved_credits(journal, handle->h_total_credits); + if (t) + atomic_sub(handle->h_total_credits, &t->t_outstanding_credits); }
void jbd2_journal_free_reserved(handle_t *handle) { - __jbd2_journal_unreserve_handle(handle); + journal_t *journal = handle->h_journal; + + /* Get j_state_lock to pin running transaction if it exists */ + read_lock(&journal->j_state_lock); + __jbd2_journal_unreserve_handle(handle, journal->j_running_transaction); + read_unlock(&journal->j_state_lock); jbd2_free_handle(handle); } EXPORT_SYMBOL(jbd2_journal_free_reserved); @@ -722,7 +729,8 @@ static void stop_this_handle(handle_t *handle) atomic_sub(handle->h_total_credits, &transaction->t_outstanding_credits); if (handle->h_rsv_handle) - __jbd2_journal_unreserve_handle(handle->h_rsv_handle); + __jbd2_journal_unreserve_handle(handle->h_rsv_handle, + transaction); if (atomic_dec_and_test(&transaction->t_updates)) wake_up(&journal->j_wait_updates);