On Thu, 21 May 2020, Johannes Weiner wrote:
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@cmpxchg.org: use mem_cgroup_disabled() in all API functions] Reported-by: Naresh Kamboju naresh.kamboju@linaro.org Debugged-by: Hugh Dickins hughd@google.com Debugged-by: Michal Hocko mhocko@kernel.org Signed-off-by: Johannes Weiner hannes@cmpxchg.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.
I like this version *a lot*, thank you. I got worried for a bit by the "#define cgroup_memory_noswap 1" when #ifndef CONFIG_MEMCG_SWAP, but now realize that fits perfectly.
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.
Absolutely okay, these are yours: I was a little uncomfortable to see me on the From line before, but it also seemed just too petty to insist that my name be removed.
(By the way, off-topic for this particular issue, but advance warning that I hope to post a couple of patches to __read_swap_cache_async() before the end of the day, first being fixup to some of your mods - I suspect you got it working well enough, and intended to come back to check a few details later, but never quite got around to that.)
From d9e7ed15d1c9248a3fd99e35e82437549154dac7 Mon Sep 17 00:00:00 2001 From: Johannes Weiner hannes@cmpxchg.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@linaro.org Debugged-by: Hugh Dickins hughd@google.com Debugged-by: Michal Hocko mhocko@kernel.org Signed-off-by: Johannes Weiner hannes@cmpxchg.org
Acked-by: Hugh Dickins hughd@google.com
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