Skip to contentSkip to conversation

FAILED: patch "[PATCH] jbd2: avoid leaking transaction credits when unreserving" failed to apply to 4.9-stable tree

PATCH [email protected] 1 participant 1 message Jun 19, 2020

Subsystems (2)
Stable branch Journalling layer for block devices (JBD2)
lore
Share & tools
lore

[email protected]

author maintainer
#0 lore raw

The patch below does not apply to the 4.9-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 <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 14ff6286309e2853aed50083c9a83328423fdd8c Mon Sep 17 00:00:00 2001
From: Jan Kara <[email protected]>
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 [email protected]
Fixes 8f7d89f36829 ("jbd2: transaction reservation support")
Reviewed-by Andreas Dilger <[email protected]>
Signed-off-by Jan Kara <[email protected]>
Link https://lore.kernel.org/r/[email protected] open here
Signed-off-by Theodore Ts'o <[email protected]>
fs/jbd2/transaction.c +11 -3
index 3dccc23cf010..e91aad3637a2 100644
@@ -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);