The patch titled
Subject: padata: Fix possible divide-by-0 panic in padata_mt_helper()
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
padata-fix-possible-divide-by-0-panic-in-padata_mt_helper.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/padata-fix-possible-divide-by-0-panic-in-padata_mt_helper.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Waiman Long <longman@xxxxxxxxxx>
Subject: padata: Fix possible divide-by-0 panic in padata_mt_helper()
Date: Tue, 6 Aug 2024 13:46:47 -0400
We are hit with a not easily reproducible divide-by-0 panic in padata.c at
bootup time.
[ 10.017908] Oops: divide error: 0000 1 PREEMPT SMP NOPTI
[ 10.017908] CPU: 26 PID: 2627 Comm: kworker/u1666:1 Not tainted 6.10.0-15.el10.x86_64 #1
[ 10.017908] Hardware name: Lenovo ThinkSystem SR950 [7X12CTO1WW]/[7X12CTO1WW], BIOS [PSE140J-2.30] 07/20/2021
[ 10.017908] Workqueue: events_unbound padata_mt_helper
[ 10.017908] RIP: 0010:padata_mt_helper+0x39/0xb0
:
[ 10.017963] Call Trace:
[ 10.017968] <TASK>
[ 10.018004] ? padata_mt_helper+0x39/0xb0
[ 10.018084] process_one_work+0x174/0x330
[ 10.018093] worker_thread+0x266/0x3a0
[ 10.018111] kthread+0xcf/0x100
[ 10.018124] ret_from_fork+0x31/0x50
[ 10.018138] ret_from_fork_asm+0x1a/0x30
[ 10.018147] </TASK>
Looking at the padata_mt_helper() function, the only way a divide-by-0
panic can happen is when ps->chunk_size is 0. The way that chunk_size is
initialized in padata_do_multithreaded(), chunk_size can be 0 when the
min_chunk in the passed-in padata_mt_job structure is 0.
Fix this divide-by-0 panic by making sure that chunk_size will be at least
1 no matter what the input parameters are.
Link: https://lkml.kernel.org/r/20240806174647.1050398-1-longman@xxxxxxxxxx
Fixes: 004ed42638f4 ("padata: add basic support for multithreaded jobs")
Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
Cc: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx>
Cc: Steffen Klassert <steffen.klassert@xxxxxxxxxxx>
Cc: Waiman Long <longman@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/padata.c | 7 +++++++
1 file changed, 7 insertions(+)
--- a/kernel/padata.c~padata-fix-possible-divide-by-0-panic-in-padata_mt_helper
+++ a/kernel/padata.c
@@ -517,6 +517,13 @@ void __init padata_do_multithreaded(stru
ps.chunk_size = max(ps.chunk_size, job->min_chunk);
ps.chunk_size = roundup(ps.chunk_size, job->align);
+ /*
+ * chunk_size can be 0 if the caller sets min_chunk to 0. So force it
+ * to at least 1 to prevent divide-by-0 panic in padata_mt_helper().`
+ */
+ if (!ps.chunk_size)
+ ps.chunk_size = 1U;
+
list_for_each_entry(pw, &works, pw_list)
if (job->numa_aware) {
int old_node = atomic_read(&last_used_nid);
_
Patches currently in -mm which might be from longman@xxxxxxxxxx are
padata-fix-possible-divide-by-0-panic-in-padata_mt_helper.patch
watchdog-handle-the-enodev-failure-case-of-lockup_detector_delay_init-separately.patch
