lists.openwall.net   lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  PHC 
Open Source and information security mailing list archives
 
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [thread-next>] [day] [month] [year] [list]
Date:   Mon, 14 Sep 2020 18:47:42 +0800
From:   Ye Bin <yebin10@...wei.com>
To:     <riteshh@...ux.ibm.com>, <jack@...e.cz>, <tytso@....edu>,
        <adilger.kernel@...ger.ca>, <jack@...e.com>,
        <linux-ext4@...r.kernel.org>
CC:     Ye Bin <yebin10@...wei.com>
Subject: [PATCH v4]  ext4: Fix dead loop in ext4_mb_new_blocks

As we test disk offline/online with running fsstress, we find fsstress
process is keeping running state.
kworker/u32:3-262   [004] ...1   140.787471: ext4_mb_discard_preallocations: dev 8,32 needed 114
....
kworker/u32:3-262   [004] ...1   140.787471: ext4_mb_discard_preallocations: dev 8,32 needed 114

ext4_mb_new_blocks
repeat:
        ext4_mb_discard_preallocations_should_retry(sb, ac, &seq)
                freed = ext4_mb_discard_preallocations
                        ext4_mb_discard_group_preallocations
                                this_cpu_inc(discard_pa_seq);
                ---> freed == 0
                seq_retry = ext4_get_discard_pa_seq_sum
                        for_each_possible_cpu(__cpu)
                                __seq += per_cpu(discard_pa_seq, __cpu);
                if (seq_retry != *seq) {
                        *seq = seq_retry;
                        ret = true;
                }

As we see seq_retry is sum of discard_pa_seq every cpu, if
ext4_mb_discard_group_preallocations return zero discard_pa_seq in this
cpu maybe increase one, so condition "seq_retry != *seq" have always
been met.
Ritesh Harjani suggest to in ext4_mb_discard_group_preallocations function we
only increase discard_pa_seq when there is some PA to free.

Fixes: 07b5b8e1ac40 ("ext4: mballoc: introduce pcpu seqcnt for freeing PA to improve ENOSPC handling")
Signed-off-by: Ye Bin <yebin10@...wei.com>
---
 fs/ext4/mballoc.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 132c118d12e1..ff47347012f4 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -4189,7 +4189,6 @@ ext4_mb_discard_group_preallocations(struct super_block *sb,
 	INIT_LIST_HEAD(&list);
 repeat:
 	ext4_lock_group(sb, group);
-	this_cpu_inc(discard_pa_seq);
 	list_for_each_entry_safe(pa, tmp,
 				&grp->bb_prealloc_list, pa_group_list) {
 		spin_lock(&pa->pa_lock);
@@ -4206,6 +4205,9 @@ ext4_mb_discard_group_preallocations(struct super_block *sb,
 		/* seems this one can be freed ... */
 		ext4_mb_mark_pa_deleted(sb, pa);
 
+		if (!free)
+			this_cpu_inc(discard_pa_seq);
+
 		/* we can trust pa_free ... */
 		free += pa->pa_free;
 
-- 
2.25.4

Powered by blists - more mailing lists