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Date:   Thu, 22 Jul 2021 07:05:50 -0700
From:   "Paul E. McKenney" <paulmck@kernel.org>
To:     Chris Clayton <chris2553@googlemail.com>
Cc:     Zhouyi Zhou <zhouzhouyi@gmail.com>,
        Oleksandr Natalenko <oleksandr@natalenko.name>,
        Matthew Wilcox <willy@infradead.org>,
        Miaohe Lin <linmiaohe@huawei.com>,
        Boqun Feng <boqun.feng@gmail.com>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        stable@vger.kernel.org, Chris Rankin <rankincj@gmail.com>,
        Josh Triplett <josh@joshtriplett.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Lai Jiangshan <jiangshanlai@gmail.com>,
        Joel Fernandes <joel@joelfernandes.org>,
        rcu <rcu@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linux-MM <linux-mm@kvack.org>,
        "Huang, Ying" <ying.huang@intel.com>,
        Greg KH <gregkh@linuxfoundation.org>
Subject: Re: linux-5.13.2: warning from kernel/rcu/tree_plugin.h:359
Message-ID: <20210722140550.GA1568948@paulmck-ThinkPad-P17-Gen-1>
Reply-To: paulmck@kernel.org
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 <2237123.PRLUojbHBq@natalenko.name>
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 <CAABZP2yh3J8+P=3PLZVaC47ymKC7PcfQCBBxjXJ9Ybn+HREbdg@mail.gmail.com>
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On Thu, Jul 22, 2021 at 08:30:10AM +0100, Chris Clayton wrote:
> On 19/07/2021 17:56, Zhouyi Zhou wrote:
> > Attached is my kernel configuration file (config-5.13.2), dmesg (dmesg.txt)
> > My qemu box's memory layout is:
> >                     total        used        free      shared
> > buff/cache   available
> > Mem:           3915          92        3764           0          58        3676
> > Swap:          2044          39        2005
> > The memory exhausting program:
> > #include <stdlib.h>
> > int main()
> > {
> >         while(1)
> >         {
> >         void *ptr =
> >                 malloc(1024*1024);
> >          memset(ptr, 0, 1024*1024);
> >         }
> >         return 0;
> > }
> > 
> 
> I'm not sure what I'm supposed to make of this. Is it that my laptop simply ran out of memory? That would be odd
> because, as I said earlier, I was simply doing a weekly archive of my system. That involved using the dar backup utility
> to create the incremental backup (which in this instance resulted in a single archive file), compressing that archive
> with xz and copying (again one at a time) it and a directory containing about 7000 source and binary rpm files from an
> internal HDD to and external HDD connected via USB
> 
> My laptop, which I've had for a little over 3 months, has 32GB of memory. I have been using dar for a few years now (and
> the version currently installed since May) and have had no trouble with it. Similarly, I've used xz to compress the
> backup archives for year and the version currently installed since December 2020. The (incremental) archive file is
> about 7GB and 1.2GB when compressed. If copying files, the largest of which is 1.2GB, serially can cause 32GB fn RAM to
> be exhausted , then we are all up the creek. So I don't see where in my normal archiving process, the memory exhaustion
> would arise from (but I'm happy to be educated on this).
> 
> Or is the memory exhaustion likely to be a side effect of the fact that two patches applied in 5.13.2 are missing a
> pre-requisite? If that's the case there, seems to no disagreement on whether the two patches (which had not been tagged
> for stable) should be reverted or the missing prerequisite should be applied (along with another, related patch that was
> in the patch set). Perhaps the stable and mm teams are resolving this issue behind the scenes, but in the meantime I
> have backported the missing patches to 5.13.4 and 5.10.52 and am currently running the former as my default kernel.

Indeed, one of the possible side effects of omitting an rcu_read_unlock()
is running out of memory.  This is because RCU never sees a quiescent
state from the task that failed to execute rcu_read_unlock(), which
in turn means that RCU can never again free any memory, which in
turn of course means that your system will sooner or later exhaust
memory.  Greg's revert should restore the balance of rcu_read_lock()
and rcu_read_unlock(), which will eliminate this particular cause of
memory exhaustion.

							Thanx, Paul

> I also have a patch that reverts the two patches that were applied to stable, so could run with that applied if it would
> be more helpful. It would, of course, leave open the races that the patches are designed to close., but if I've manually
> run swapoff more than once or twice in the twenty years I've been using Linux-based systems, I'd be very surprised.
> 
> > On Tue, Jul 20, 2021 at 12:47 AM Zhouyi Zhou <zhouzhouyi@gmail.com> wrote:
> >>
> >> I downloaded linux-5.13.2, configure and compile the kernel with
> >> CONFIG_LOCKDEP=y
> >> CONFIG_LOCK_DEBUGGING_SUPPORT=y
> >> CONFIG_PROVE_LOCKING=y
> >> CONFIG_DEBUG_SPINLOCK=y
> >> CONFIG_DEBUG_LOCK_ALLOC=y
> >> install the kernel on a qemu box, then run following C Program
> >> #include <stdlib.h>
> >> int main()
> >> {
> >>         while(1)
> >>         {
> >>                 malloc(1024*1024);
> >>         }
> >>         return 0;
> >> }
> >> And following is the dmesg:
> >> [   96.155017] ------------[ cut here ]------------
> >> [   96.155030] WARNING: CPU: 10 PID: 770 at
> >> kernel/rcu/tree_plugin.h:359 rcu_note_context_switch+0x91/0x610
> >> [   96.155074] Modules linked in: ppdev intel_rapl_msr
> >> intel_rapl_common crct10dif_pclmul crc32_pclmul ghash_clmulni_intel
> >> bochs_drm aesni_intel drm_vram_helper evdev crypto_simd drm_ttm_helper
> >> snd_pcm cryptd ttm snd_timer parport_pc serio_raw drm_kms_helper sg
> >> snd parport soundcore drm pcspkr button ip_tables autofs4 psmouse
> >> sr_mod i2c_piix4 sd_mod crc32c_intel t10_pi cdrom i2c_core e1000
> >> ata_generic floppy
> >> [   96.155180] CPU: 10 PID: 770 Comm: containerd Not tainted 5.13.2 #1
> >> [   96.155185] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
> >> BIOS rel-1.11.0-0-g63451fca13-prebuilt.qemu-project.org 04/01/2014
> >> [   96.155189] RIP: 0010:rcu_note_context_switch+0x91/0x610
> >> [   96.155195] Code: ff 74 0f 65 8b 05 a7 10 e5 7e 85 c0 0f 84 22 01
> >> 00 00 45 84 ed 75 15 65 48 8b 04 25 80 7f 01 00 8b b0 44 03 00 00 85
> >> f6 7e 02 <0f> 0b 65 48 8b 04 25 80 7f 01 00 8b 88 44 03 00 00 85 c9 7e
> >> 0f 41
> >> [   96.155200] RSP: 0000:ffffc90000a8bc50 EFLAGS: 00010002
> >> [   96.155204] RAX: ffff88810830c300 RBX: ffff88813bcae680 RCX: 0000000000000000
> >> [   96.155208] RDX: 0000000000000002 RSI: 0000000000000001 RDI: 0000000000000001
> >> [   96.155210] RBP: ffffc90000a8bcd0 R08: 0000000000000001 R09: 0000000000000001
> >> [   96.155213] R10: 0000000000000000 R11: ffffffff81319b93 R12: ffff88810830c300
> >> [   96.155216] R13: 0000000000000000 R14: ffff88813bcad958 R15: 0000000000004970
> >> [   96.155220] FS:  00007fc09cff9700(0000) GS:ffff88813bc80000(0000)
> >> knlGS:0000000000000000
> >> [   96.155223] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> >> [   96.155226] CR2: 00005594d2ff0530 CR3: 0000000103be4001 CR4: 0000000000060ee0
> >> [   96.155233] Call Trace:
> >> [   96.155243]  __schedule+0xda/0xa30
> >> [   96.155283]  schedule+0x46/0xf0
> >> [   96.155289]  io_schedule+0x12/0x40
> >> [   96.155295]  __lock_page_or_retry+0x1f9/0x510
> >> [   96.155319]  ? __page_cache_alloc+0x140/0x140
> >> [   96.155345]  do_swap_page+0x33f/0x930
> >> [   96.155364]  __handle_mm_fault+0xa54/0x1550
> >> [   96.155390]  handle_mm_fault+0x17f/0x420
> >> [   96.155400]  do_user_addr_fault+0x1be/0x770
> >> [   96.155422]  exc_page_fault+0x69/0x280
> >> [   96.155435]  ? asm_exc_page_fault+0x8/0x30
> >> [   96.155443]  asm_exc_page_fault+0x1e/0x30
> >> [   96.155448] RIP: 0033:0x5594d15ec98f
> >> [   96.155454] Code: 44 24 58 48 85 c0 48 b9 00 e4 0b 54 02 00 00 00
> >> 48 0f 44 c1 48 89 44 24 58 eb 05 48 8b 44 24 58 48 89 04 24 e8 e2 c9
> >> 9c ff 90 <48> 8b 05 9a 3b a0 01 48 8b 4c 24 50 48 89 0c 24 48 8d 15 9a
> >> c4 ec
> >> [   96.155457] RSP: 002b:000000c0001f7f80 EFLAGS: 00010206
> >> [   96.155462] RAX: 0000000000000000 RBX: 00005594d0f9cf55 RCX: fffffffffffffff8
> >> [   96.155465] RDX: 0000000000000000 RSI: 0000000000000000 RDI: 00005594d0fa2d01
> >> [   96.155467] RBP: 000000c0001f7fc0 R08: 0000000000000000 R09: 0000000000000000
> >> [   96.155470] R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000000004
> >> [   96.155472] R13: 0000000000000013 R14: 00005594d1ee96e6 R15: 0000000000000039
> >> [   96.155495] irq event stamp: 10464
> >> [   96.155497] hardirqs last  enabled at (10463): [<ffffffff81c0a574>]
> >> _raw_spin_unlock_irq+0x24/0x50
> >> [   96.155508] hardirqs last disabled at (10464): [<ffffffff81c01882>]
> >> __schedule+0x412/0xa30
> >> [   96.155512] softirqs last  enabled at (8668): [<ffffffff82000401>]
> >> __do_softirq+0x401/0x51b
> >> [   96.155517] softirqs last disabled at (8657): [<ffffffff81129c22>]
> >> irq_exit_rcu+0x142/0x150
> >> [   96.155531] ---[ end trace 165ff31fd86ffc12 ]---
> >>
> >> [   96.177669] =============================
> >> [   96.177693] [ BUG: Invalid wait context ]
> >> [   96.177717] 5.13.2 #1 Tainted: G        W
> >> [   96.177743] -----------------------------
> >> [   96.177765] containerd/770 is trying to lock:
> >> [   96.177790] ffff88813ba69b30 (&cache->alloc_lock){+.+.}-{3:3}, at:
> >> get_swap_page+0x126/0x200
> >> [   96.177867] other info that might help us debug this:
> >> [   96.177894] context-{4:4}
> >> [   96.177910] 3 locks held by containerd/770:
> >> [   96.177934]  #0: ffff88810815ea28 (&mm->mmap_lock#2){++++}-{3:3},
> >> at: do_user_addr_fault+0x115/0x770
> >> [   96.177999]  #1: ffffffff82915020 (rcu_read_lock){....}-{1:2}, at:
> >> get_swap_device+0x33/0x140
> >> [   96.178057]  #2: ffffffff82955ba0 (fs_reclaim){+.+.}-{0:0}, at:
> >> __fs_reclaim_acquire+0x5/0x30
> >> [   96.178115] stack backtrace:
> >> [   96.178133] CPU: 1 PID: 770 Comm: containerd Tainted: G        W
> >>      5.13.2 #1
> >> [   96.178183] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
> >> BIOS rel-1.11.0-0-g63451fca13-prebuilt.qemu-project.org 04/01/2014
> >> [   96.178254] Call Trace:
> >> [   96.178274]  dump_stack+0x82/0xa4
> >> [   96.178314]  __lock_acquire+0x9a5/0x20a0
> >> [   96.178347]  ? find_held_lock+0x3a/0xb0
> >> [   96.178381]  lock_acquire+0xe9/0x320
> >> [   96.178405]  ? get_swap_page+0x126/0x200
> >> [   96.178433]  ? _raw_spin_unlock+0x29/0x40
> >> [   96.178461]  ? page_vma_mapped_walk+0x3a3/0x960
> >> [   96.178491]  __mutex_lock+0x99/0x980
> >> [   96.178515]  ? get_swap_page+0x126/0x200
> >> [   96.178541]  ? find_held_lock+0x3a/0xb0
> >> [   96.178577]  ? get_swap_page+0x126/0x200
> >> [   96.178603]  ? page_referenced+0xd5/0x170
> >> [   96.178637]  ? lock_release+0x1b4/0x300
> >> [   96.178663]  ? get_swap_page+0x126/0x200
> >> [   96.178698]  get_swap_page+0x126/0x200
> >> [   96.178725]  add_to_swap+0x14/0x60
> >> [   96.178749]  shrink_page_list+0xb13/0xe70
> >> [   96.178787]  shrink_inactive_list+0x243/0x550
> >> [   96.178819]  shrink_lruvec+0x4fd/0x780
> >> [   96.178849]  ? shrink_node+0x257/0x7c0
> >> [   96.178873]  shrink_node+0x257/0x7c0
> >> [   96.178900]  do_try_to_free_pages+0xdd/0x410
> >> [   96.178929]  try_to_free_pages+0x110/0x300
> >> [   96.178966]  __alloc_pages_slowpath.constprop.126+0x2ae/0xfa0
> >> [   96.179002]  ? lock_release+0x1b4/0x300
> >> [   96.179028]  __alloc_pages+0x37d/0x400
> >> [   96.179054]  alloc_pages_vma+0x73/0x1d0
> >> [   96.179878]  __read_swap_cache_async+0xb8/0x280
> >> [   96.180684]  swap_cluster_readahead+0x194/0x270
> >> [   96.181459]  ? swapin_readahead+0x62/0x530
> >> [   96.182008]  swapin_readahead+0x62/0x530
> >> [   96.182558]  ? find_held_lock+0x3a/0xb0
> >> [   96.183109]  ? lookup_swap_cache+0x5c/0x1c0
> >> [   96.183657]  ? lock_release+0x1b4/0x300
> >> [   96.184207]  ? do_swap_page+0x232/0x930
> >> [   96.184753]  do_swap_page+0x232/0x930
> >> [   96.185326]  __handle_mm_fault+0xa54/0x1550
> >> [   96.185850]  handle_mm_fault+0x17f/0x420
> >> [   96.186361]  do_user_addr_fault+0x1be/0x770
> >> [   96.186880]  exc_page_fault+0x69/0x280
> >> [   96.187382]  ? asm_exc_page_fault+0x8/0x30
> >> [   96.187879]  asm_exc_page_fault+0x1e/0x30
> >> [   96.188363] RIP: 0033:0x5594d0f78da4
> >> [   96.188829] Code: cc cc cc cc cc cc 48 8b 0d 39 d2 01 02 64 48 8b
> >> 09 48 3b 61 10 76 3d 48 83 ec 28 48 89 6c 24 20 48 8d 6c 24 20 48 8b
> >> 44 24 30 <48> 8b 08 48 89 0c 24 48 89 44 24 08 c6 44 24 10 01 e8 76 f4
> >> ff ff
> >> [   96.189894] RSP: 002b:000000c0001f7de8 EFLAGS: 00010216
> >> [   96.190406] RAX: 00005594d2308160 RBX: 0000000000000000 RCX: 000000c0004ea480
> >> [   96.190902] RDX: 000000c0002a4270 RSI: 0000000000000010 RDI: 0000000000000011
> >> [   96.191394] RBP: 000000c0001f7e08 R08: 0000000000000002 R09: 0000000000000011
> >> [   96.191891] R10: 00005594d22f6ce0 R11: 00005594d1ee96e4 R12: ffffffffffffffff
> >> [   96.192396] R13: 0000000000000028 R14: 0000000000000027 R15: 0000000000000200
> >> [  115.344546] exaust invoked oom-killer:
> >> gfp_mask=0x100dca(GFP_HIGHUSER_MOVABLE|__GFP_ZERO), order=0,
> >> oom_score_adj=0
> >> [  115.346019] CPU: 1 PID: 969 Comm: exaust Tainted: G        W
> >>  5.13.2 #1
> >> [  115.346569] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
> >> BIOS rel-1.11.0-0-g63451fca13-prebuilt.qemu-project.org 04/01/2014
> >> [  115.347712] Call Trace:
> >> [  115.348287]  dump_stack+0x82/0xa4
> >> [  115.348867]  dump_header+0x55/0x3f0
> >> [  115.349491]  oom_kill_process+0x160/0x210
> >> [  115.350068]  out_of_memory+0x10b/0x630
> >> [  115.350646]  __alloc_pages_slowpath.constprop.126+0xec7/0xfa0
> >> [  115.351255]  __alloc_pages+0x37d/0x400
> >> [  115.351861]  alloc_pages_vma+0x73/0x1d0
> >> [  115.352449]  __handle_mm_fault+0xe1b/0x1550
> >> [  115.353042]  handle_mm_fault+0x17f/0x420
> >> [  115.353646]  do_user_addr_fault+0x1be/0x770
> >> [  115.354239]  exc_page_fault+0x69/0x280
> >> [  115.354833]  ? asm_exc_page_fault+0x8/0x30
> >> [  115.355428]  asm_exc_page_fault+0x1e/0x30
> >> [  115.356021] RIP: 0033:0x7fe8ee633543
> >> [  115.356617] Code: Unable to access opcode bytes at RIP 0x7fe8ee633519.
> >> [  115.357245] RSP: 002b:00007fff742c68c8 EFLAGS: 00010206
> >> [  115.357857] RAX: 00007fe798041010 RBX: 0000000000000000 RCX: 00007fe7980fd000
> >> [  115.358469] RDX: 00007fe798141000 RSI: 0000000000000000 RDI: 00007fe798041010
> >> [  115.359077] RBP: 00007fff742c68e0 R08: 00000000ffffffff R09: 0000000000000000
> >> [  115.359686] R10: 0000000000000022 R11: 0000000000000246 R12: 0000561abe3fa060
> >> [  115.360300] R13: 00007fff742c69c0 R14: 0000000000000000 R15: 0000000000000000
> >> [  115.361313] Mem-Info:
> >> [  115.362285] active_anon:188386 inactive_anon:764572 isolated_anon:64
> >>                 active_file:61 inactive_file:0 isolated_file:0
> >>                 unevictable:0 dirty:0 writeback:2
> >>                 slab_reclaimable:6676 slab_unreclaimable:6200
> >>                 mapped:155 shmem:180 pagetables:3124 bounce:0
> >>                 free:25647 free_pcp:0 free_cma:0
> >> [  115.366889] Node 0 active_anon:782092kB inactive_anon:3029744kB
> >> active_file:244kB inactive_file:0kB unevictable:0kB
> >> isolated(anon):256kB isolated(file):0kB mapped:620kB dirty:0kB
> >> writeback:8kB shmem:720kB shmem_thp: 0kB shmem_pmdmapped: 0kB
> >> anon_thp: 0kB writeback_tmp:0kB kernel_stack:3904kB pagetables:12496kB
> >> all_unreclaimable? no
> >> [  115.369378] Node 0 DMA free:15296kB min:260kB low:324kB high:388kB
> >> reserved_highatomic:0KB active_anon:0kB inactive_anon:0kB
> >> active_file:0kB inactive_file:0kB unevictable:0kB writepending:0kB
> >> present:15992kB managed:15360kB mlocked:0kB bounce:0kB free_pcp:0kB
> >> local_pcp:0kB free_cma:0kB
> >> [  115.372121] lowmem_reserve[]: 0 2925 3874 3874
> >> [  115.373195] Node 0 DMA32 free:54436kB min:50824kB low:63528kB
> >> high:76232kB reserved_highatomic:0KB active_anon:819596kB
> >> inactive_anon:2135980kB active_file:48kB inactive_file:24kB
> >> unevictable:0kB writepending:8kB present:3129212kB managed:3021488kB
> >> mlocked:0kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB
> >> [  115.375958] lowmem_reserve[]: 0 0 949 949
> >> [  115.377064] Node 0 Normal free:32856kB min:32880kB low:37004kB
> >> high:41128kB reserved_highatomic:0KB active_anon:2232kB
> >> inactive_anon:853384kB active_file:80kB inactive_file:76kB
> >> unevictable:0kB writepending:0kB present:1048576kB managed:972400kB
> >> mlocked:0kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB
> >> [  115.380050] lowmem_reserve[]: 0 0 0 0
> >> [  115.380908] Node 0 DMA: 0*4kB 0*8kB 0*16kB 0*32kB 1*64kB (U)
> >> 1*128kB (U) 1*256kB (U) 1*512kB (U) 0*1024kB 1*2048kB (M) 3*4096kB (M)
> >> = 15296kB
> >> [  115.382728] Node 0 DMA32: 86*4kB (UM) 52*8kB (UME) 33*16kB (UM)
> >> 28*32kB (UME) 11*64kB (U) 2*128kB (UE) 0*256kB 1*512kB (U) 2*1024kB
> >> (UM) 2*2048kB (ME) 11*4096kB (M) = 54856kB
> >> [  115.384560] Node 0 Normal: 597*4kB (UME) 904*8kB (UME) 414*16kB
> >> (UME) 187*32kB (UME) 64*64kB (UME) 19*128kB (UME) 3*256kB (U) 3*512kB
> >> (UE) 2*1024kB (M) 0*2048kB 0*4096kB = 33108kB
> >> [  115.386558] Node 0 hugepages_total=0 hugepages_free=0
> >> hugepages_surp=0 hugepages_size=1048576kB
> >> [  115.387543] Node 0 hugepages_total=0 hugepages_free=0
> >> hugepages_surp=0 hugepages_size=2048kB
> >> [  115.388503] 61467 total pagecache pages
> >> [  115.389532] 61242 pages in swap cache
> >> [  115.390450] Swap cache stats: add 523756, delete 462538, find 69/171
> >> [  115.391383] Free swap  = 0kB
> >> [  115.392312] Total swap = 2094076kB
> >> [  115.393506] 1048445 pages RAM
> >> [  115.394538] 0 pages HighMem/MovableOnly
> >> [  115.395514] 46133 pages reserved
> >> [  115.396525] 0 pages hwpoisoned
> >> [  115.397824] Tasks state (memory values in pages):
> >> [  115.398778] [  pid  ]   uid  tgid total_vm      rss pgtables_bytes
> >> swapents oom_score_adj name
> >> [  115.399792] [    312]     0   312     6603      217    98304
> >> 181             0 systemd-journal
> >> [  115.400749] [    339]     0   339     5562        1    69632
> >> 395         -1000 systemd-udevd
> >> [  115.401869] [    379]   101   379    23271       17    81920
> >> 197             0 systemd-timesyn
> >> [  115.402873] [    388]   107   388     1707        7    53248
> >> 101             0 rpcbind
> >> [  115.403869] [    479]     0   479     2373       39    53248
> >> 284             0 dhclient
> >> [  115.404849] [    485]     0   485     2120        8    53248
> >> 43             0 cron
> >> [  115.406291] [    487]     0   487     4869       44    77824
> >> 197             0 systemd-logind
> >> [  115.407536] [    494]   104   494     2247       58    57344
> >> 80          -900 dbus-daemon
> >> [  115.408772] [    501]     0   501    56457        0    86016
> >> 226             0 rsyslogd
> >> [  115.410041] [    503]     0   503   315093      769   311296
> >> 3943             0 containerd
> >> [  115.411289] [    507]     0   507     1404        2    45056
> >> 26             0 agetty
> >> [  115.412563] [    521]     0   521    27588      235   110592
> >> 1678             0 unattended-upgr
> >> [  115.413834] [    860]     0   860     3964       28    73728
> >> 187         -1000 sshd
> >> [  115.415062] [    866]   106   866     5015       19    81920
> >> 187             0 exim4
> >> [  115.416286] [    901]     0   901     4233        1    73728
> >> 281             0 sshd
> >> [  115.417534] [    928]     0   928     5287       57    73728
> >> 280             0 systemd
> >> [  115.418755] [    929]     0   929     5710       77    90112
> >> 488             0 (sd-pam)
> >> [  115.419921] [    943]     0   943     2013        1    53248
> >> 407             0 bash
> >> [  115.421061] [    969]     0   969  1402762   888995 11276288
> >> 513120             0 exaust
> >> [  115.421973] [    970]     0   970     4233      272    77824
> >> 5             0 sshd
> >> [  115.422840] [    976]     0   976     1980      297    53248
> >> 64             0 bash
> >> [  115.423664] oom-kill:constraint=CONSTRAINT_NONE,nodemask=(null),cpuset=/,mems_allowed=0,global_oom,task_memcg=/user.slice/user-0.slice/session-1.scope,task=exaust,pid=969,uid=0
> >> [  115.425344] Out of memory: Killed process 969 (exaust)
> >> total-vm:5611048kB, anon-rss:3555976kB, file-rss:4kB, shmem-rss:0kB,
> >> UID:0 pgtables:11012kB oom_score_adj:0
> >> [  115.912696] oom_reaper: reaped process 969 (exaust), now
> >> anon-rss:0kB, file-rss:0kB, shmem-rss:0kB
> >>
> >>
> >> I can tell from above that:  [   96.177999]  #1: ffffffff82915020
> >> (rcu_read_lock){....}-{1:2}, at: get_swap_device+0x33/0x140
> >>  get_swap_device did help the rcu_read_lock
> >>
> >> Thanks
> >> Zhouyi
> >>
> >> On Mon, Jul 19, 2021 at 8:23 PM Oleksandr Natalenko
> >> <oleksandr@natalenko.name> wrote:
> >>>
> >>> On pondělí 19. července 2021 14:16:04 CEST Matthew Wilcox wrote:
> >>>> On Mon, Jul 19, 2021 at 02:12:15PM +0200, Oleksandr Natalenko wrote:
> >>>>> On pondělí 19. července 2021 14:08:37 CEST Miaohe Lin wrote:
> >>>>>> On 2021/7/19 19:59, Oleksandr Natalenko wrote:
> >>>>>>> On pondělí 19. července 2021 13:50:07 CEST Miaohe Lin wrote:
> >>>>>>>> On 2021/7/19 19:22, Matthew Wilcox wrote:
> >>>>>>>>> On Mon, Jul 19, 2021 at 07:12:58PM +0800, Miaohe Lin wrote:
> >>>>>>>>>> When in the commit 2799e77529c2a, we're using the percpu_ref to
> >>>>>>>>>> serialize
> >>>>>>>>>> against concurrent swapoff, i.e. there's percpu_ref inside
> >>>>>>>>>> get_swap_device() instead of rcu_read_lock(). Please see commit
> >>>>>>>>>> 63d8620ecf93 ("mm/swapfile: use percpu_ref to serialize against
> >>>>>>>>>> concurrent swapoff") for detail.
> >>>>>>>>>
> >>>>>>>>> Oh, so this is a backport problem.  2799e77529c2 was backported
> >>>>>>>>> without
> >>>>>>>>> its prerequisite 63d8620ecf93.  Greg, probably best to just drop
> >>>>>>>>
> >>>>>>>> Yes, they're posted as a patch set:
> >>>>>>>>
> >>>>>>>> https://lkml.kernel.org/r/20210426123316.806267-1-linmiaohe@huawei.co
> >>>>>>>> m
> >>>>>>>>
> >>>>>>>>> 2799e77529c2 from all stable trees; the race described is not very
> >>>>>>>>> important (swapoff vs reading a page back from that swap device).
> >>>>>>>>> .
> >>>>>>>>
> >>>>>>>> The swapoff races with reading a page back from that swap device
> >>>>>>>> should
> >>>>>>>> be
> >>>>>>>> really uncommon as most users only do swapoff when the system is
> >>>>>>>> going to
> >>>>>>>> shutdown.
> >>>>>>>>
> >>>>>>>> Sorry for the trouble!
> >>>>>>>
> >>>>>>> git log --oneline v5.13..v5.13.3 --author="Miaohe Lin"
> >>>>>>> 11ebc09e50dc mm/zswap.c: fix two bugs in zswap_writeback_entry()
> >>>>>>> 95d192da198d mm/z3fold: use release_z3fold_page_locked() to release
> >>>>>>> locked
> >>>>>>> z3fold page
> >>>>>>> ccb7848e2344 mm/z3fold: fix potential memory leak in
> >>>>>>> z3fold_destroy_pool()
> >>>>>>> 9f7229c901c1 mm/huge_memory.c: don't discard hugepage if other
> >>>>>>> processes
> >>>>>>> are mapping it
> >>>>>>> f13259175e4f mm/huge_memory.c: add missing read-only THP checking in
> >>>>>>> transparent_hugepage_enabled()
> >>>>>>> afafd371e7de mm/huge_memory.c: remove dedicated macro
> >>>>>>> HPAGE_CACHE_INDEX_MASK a533a21b692f mm/shmem: fix shmem_swapin() race
> >>>>>>> with swapoff
> >>>>>>> c3b39134bbd0 swap: fix do_swap_page() race with swapoff
> >>>>>>>
> >>>>>>> Do you suggest reverting "mm/shmem: fix shmem_swapin() race with
> >>>>>>> swapoff"
> >>>>>>> as well?
> >>>>>>
> >>>>>> This patch also rely on its prerequisite 63d8620ecf93. I think we should
> >>>>>> either revert any commit in this series or just backport the entire
> >>>>>> series.
> >>>>>
> >>>>> Then why not just pick up 2 more patches instead of dropping 2 patches.
> >>>>> Greg, could you please make sure the whole series from [1] gets pulled?
> >>>>
> >>>> Because none of these patches should have been backported in the first
> >>>> place.  It's just not worth the destabilisation.
> >>>
> >>> What about the rest then?
> >>>
> >>> git log --oneline v5.13..v5.13.3 -- mm/ | wc -l
> >>> 18
> >>>
> >>> Those look to be fixes, these ones too.
> >>>
> >>> --
> >>> Oleksandr Natalenko (post-factum)
> >>>
> >>>