The patch titled
Subject: swapfile: fix soft lockup in scan_swap_map_slots
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
swapfile-fix-soft-lockup-in-scan_swap_map_slots.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/swapfile-fix-soft-lockup-in-scan_swap_map_slots.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: Chen Wandun <chenwandun@xxxxxxxxxx>
Subject: swapfile: fix soft lockup in scan_swap_map_slots
Date: Fri, 18 Nov 2022 21:38:50 +0800
A softlockup occurs in scan free swap slot under huge memory pressure.
The test scenario is: 64 CPU cores, 64GB memory, and 28 zram devices, the
disksize of each zram device is 50MB.
LATENCY_LIMIT is used to prevent softlockups in scan_swap_map_slots(), but
the real loop number would more than LATENCY_LIMIT because of "goto checks
and goto scan" repeatly without decreasing latency limit.
In order to fix it, decrease latency_ration in advance.
There is also a suspicious place that will cause softlockups in
get_swap_pages(). In this function, the "goto start_over" may result in
continuous scanning of the swap partition. If there is no cond_sched in
scan_swap_map_slots(), it would cause a softlockup (I am not sure about
this).
WARN: soft lockup - CPU#11 stuck for 11s! [kswapd0:466]
CPU: 11 PID: 466 Comm: kswapd@ Kdump: loaded Tainted: G
dump backtrace+0x0/0x1le4
show stack+0x20/@x2c
dump_stack+0xd8/0x140
watchdog print_info+0x48/0x54
watchdog_process_before_softlockup+0x98/0xa0
watchdog_timer_fn+0xlac/0x2d0
hrtimer_rum_queues+0xb0/0x130
hrtimer_interrupt+0x13c/0x3c0
arch_timer_handler_virt+0x3c/0x50
handLe_percpu_devid_irq+0x90/0x1f4
handle domain irq+0x84/0x100
gic_handle_irq+0x88/0x2b0
e11 ira+0xhB/Bx140
scan_swap_map_slots+0x678/0x890
get_swap_pages+0x29c/0x440
get_swap_page+0x120/0x2e0
add_to_swap+UX2U/0XyC
shrink_page_list+0x5d0/0x152c
shrink_inactive_list+0xl6c/Bx500
shrink_lruvec+0x270/0x304
WARN: soft lockup - CPU#32 stuck for 11s! [stress-ng:309915]
watchdog_timer_fn+0x1ac/0x2d0
__run_hrtimer+0x98/0x2a0
__hrtimer_run_queues+0xb0/0x130
hrtimer_interrupt+0x13c/0x3c0
arch_timer_handler_virt+0x3c/0x50
handle_percpu_devid_irq+0x90/0x1f4
__handle_domain_irq+0x84/0x100
gic_handle_irq+0x88/0x2b0
el1_irq+0xb8/0x140
get_swap_pages+0x1e8/0x440
get_swap_page+0x1c8/0x2e0
add_to_swap+0x20/0x9c
shrink_page_list+0x5d0/0x152c
reclaim_pages+0x160/0x310
madvise_cold_or_pageout_pte_range+0x7bc/0xe3c
walk_pmd_range.isra.0+0xac/0x22c
walk_pud_range+0xfc/0x1c0
walk_pgd_range+0x158/0x1b0
__walk_page_range+0x64/0x100
walk_page_range+0x104/0x150
Link: https://lkml.kernel.org/r/20221118133850.3360369-1-chenwandun@xxxxxxxxxx
Fixes: 048c27fd7281 ("[PATCH] swap: scan_swap_map latency breaks")
Signed-off-by: Chen Wandun <chenwandun@xxxxxxxxxx>
Cc: Hugh Dickins <hugh@xxxxxxxxxxx>
Cc: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
Cc: Nanyong Sun <sunnanyong@xxxxxxxxxx>
Cc: Huang Ying <ying.huang@xxxxxxxxx>
Cc: <xialonglong1@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/swapfile.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
--- a/mm/swapfile.c~swapfile-fix-soft-lockup-in-scan_swap_map_slots
+++ a/mm/swapfile.c
@@ -973,23 +973,23 @@ done:
scan:
spin_unlock(&si->lock);
while (++offset <= READ_ONCE(si->highest_bit)) {
- if (swap_offset_available_and_locked(si, offset))
- goto checks;
if (unlikely(--latency_ration < 0)) {
cond_resched();
latency_ration = LATENCY_LIMIT;
scanned_many = true;
}
+ if (swap_offset_available_and_locked(si, offset))
+ goto checks;
}
offset = si->lowest_bit;
while (offset < scan_base) {
- if (swap_offset_available_and_locked(si, offset))
- goto checks;
if (unlikely(--latency_ration < 0)) {
cond_resched();
latency_ration = LATENCY_LIMIT;
scanned_many = true;
}
+ if (swap_offset_available_and_locked(si, offset))
+ goto checks;
offset++;
}
spin_lock(&si->lock);
_
Patches currently in -mm which might be from chenwandun@xxxxxxxxxx are
swapfile-fix-soft-lockup-in-scan_swap_map_slots.patch
