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Date: Thu, 21 May 2020 17:58:55 -0400 From: Johannes Weiner <hannes@...xchg.org> To: Hugh Dickins <hughd@...gle.com> Cc: Michal Hocko <mhocko@...nel.org>, Naresh Kamboju <naresh.kamboju@...aro.org>, Chris Down <chris@...isdown.name>, Yafang Shao <laoar.shao@...il.com>, Anders Roxell <anders.roxell@...aro.org>, "Linux F2FS DEV, Mailing List" <linux-f2fs-devel@...ts.sourceforge.net>, linux-ext4 <linux-ext4@...r.kernel.org>, linux-block <linux-block@...r.kernel.org>, Andrew Morton <akpm@...ux-foundation.org>, open list <linux-kernel@...r.kernel.org>, Linux-Next Mailing List <linux-next@...r.kernel.org>, linux-mm <linux-mm@...ck.org>, Arnd Bergmann <arnd@...db.de>, Andreas Dilger <adilger.kernel@...ger.ca>, Jaegeuk Kim <jaegeuk@...nel.org>, Theodore Ts'o <tytso@....edu>, Chao Yu <chao@...nel.org>, Andrea Arcangeli <aarcange@...hat.com>, Matthew Wilcox <willy@...radead.org>, Chao Yu <yuchao0@...wei.com>, lkft-triage@...ts.linaro.org, Roman Gushchin <guro@...com>, Cgroups <cgroups@...r.kernel.org> Subject: Re: mm: mkfs.ext4 invoked oom-killer on i386 - pagecache_get_page On Thu, May 21, 2020 at 01:06:28PM -0700, Hugh Dickins wrote: > On Thu, 21 May 2020, Johannes Weiner wrote: > > do_memsw_account() used to be automatically false when the cgroup > > controller was disabled. Now that it's replaced by > > cgroup_memory_noswap, for which this isn't true, make the > > mem_cgroup_disabled() checks explicit in the swap control API. > > > > [hannes@...xchg.org: use mem_cgroup_disabled() in all API functions] > > Reported-by: Naresh Kamboju <naresh.kamboju@...aro.org> > > Debugged-by: Hugh Dickins <hughd@...gle.com> > > Debugged-by: Michal Hocko <mhocko@...nel.org> > > Signed-off-by: Johannes Weiner <hannes@...xchg.org> > > --- > > mm/memcontrol.c | 47 +++++++++++++++++++++++++++++++++++++++++------ > > 1 file changed, 41 insertions(+), 6 deletions(-) > > I'm certainly not against a mem_cgroup_disabled() check in the only > place that's been observed to need it, as a fixup to merge into your > original patch; but this seems rather an over-reaction - and I'm a > little surprised that setting mem_cgroup_disabled() doesn't just > force cgroup_memory_noswap, saving repetitious checks elsewhere > (perhaps there's a difficulty in that, I haven't looked). Fair enough, I changed it to set the flag at initialization time if mem_cgroup_disabled(). I was never a fan of the old flags, where it was never clear what was commandline, and what was internal runtime state - do_swap_account? really_do_swap_account? But I think it's straight-forward in this case now. > Historically, I think we've added mem_cgroup_disabled() checks > (accessing a cacheline we'd rather avoid) where they're necessary, > rather than at every "interface". To me that always seemed like bugs waiting to happen. Like this one! It's a jump label nowadays, so I've been liberal with these to avoid subtle bugs. > And you seem to be in a very "goto out" mood today - we all have > our "goto out" days, alternating with our "return 0" days :) :-) But I agree, best to keep this fixup self-contained and defer anything else to separate cleanup patches. How about the below? It survives a swaptest with cgroup_disable=memory for me. Hugh, I started with your patch, which is why I kept you as the author, but as the patch now (and arguably the previous one) is sufficiently different, I dropped that now. I hope that's okay. --- >From d9e7ed15d1c9248a3fd99e35e82437549154dac7 Mon Sep 17 00:00:00 2001 From: Johannes Weiner <hannes@...xchg.org> Date: Thu, 21 May 2020 17:44:25 -0400 Subject: [PATCH] mm: memcontrol: prepare swap controller setup for integration fix Fix crash with cgroup_disable=memory: > > > > + mkfs -t ext4 /dev/disk/by-id/ata-TOSHIBA_MG04ACA100N_Y8NRK0BPF6XF > > > > mke2fs 1.43.8 (1-Jan-2018) > > > > Creating filesystem with 244190646 4k blocks and 61054976 inodes > > > > Filesystem UUID: 3bb1a285-2cb4-44b4-b6e8-62548f3ac620 > > > > Superblock backups stored on blocks: > > > > 32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208, > > > > 4096000, 7962624, 11239424, 20480000, 23887872, 71663616, 78675968, > > > > 102400000, 214990848 > > > > Allocating group tables: 0/7453 done > > > > Writing inode tables: 0/7453 done > > > > Creating journal (262144 blocks): [ 35.502102] BUG: kernel NULL > > > > pointer dereference, address: 000000c8 > > > > [ 35.508372] #PF: supervisor read access in kernel mode > > > > [ 35.513506] #PF: error_code(0x0000) - not-present page > > > > [ 35.518638] *pde = 00000000 > > > > [ 35.521514] Oops: 0000 [#1] SMP > > > > [ 35.524652] CPU: 0 PID: 145 Comm: kswapd0 Not tainted > > > > 5.7.0-rc6-next-20200519+ #1 > > > > [ 35.532121] Hardware name: Supermicro SYS-5019S-ML/X11SSH-F, BIOS > > > > 2.2 05/23/2018 > > > > [ 35.539507] EIP: mem_cgroup_get_nr_swap_pages+0x28/0x60 Swap accounting used to be implied-disabled when the cgroup controller was disabled. Restore that for the new cgroup_memory_noswap, so that we bail out of this function instead of dereferencing a NULL memcg. Reported-by: Naresh Kamboju <naresh.kamboju@...aro.org> Debugged-by: Hugh Dickins <hughd@...gle.com> Debugged-by: Michal Hocko <mhocko@...nel.org> Signed-off-by: Johannes Weiner <hannes@...xchg.org> --- mm/memcontrol.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 3e000a316b59..e3b785d6e771 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -7075,7 +7075,11 @@ static struct cftype memsw_files[] = { static int __init mem_cgroup_swap_init(void) { - if (mem_cgroup_disabled() || cgroup_memory_noswap) + /* No memory control -> no swap control */ + if (mem_cgroup_disabled()) + cgroup_memory_noswap = true; + + if (cgroup_memory_noswap) return 0; WARN_ON(cgroup_add_dfl_cftypes(&memory_cgrp_subsys, swap_files)); -- 2.26.2
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