On 2025-11-07 09:43, Mathieu Desnoyers wrote:
On 2025-11-06 19:32, Shakeel Butt wrote:
[...]
[ 14.858862][ T67] BUG: Bad rss-counter state mm:ffff8881000655c0
type:MM_ANONPAGES val:0 Comm:kworker/u9:0 Pid:67
[ 14.894890][ T69] BUG: Bad rss-counter state mm:ffff888100061cc0
type:MM_FILEPAGES val:0 Comm:kworker/u9:0 Pid:69
[ 14.896108][ T69] BUG: Bad rss-counter state mm:ffff888100061cc0
type:MM_ANONPAGES val:0 Comm:kworker/u9:0 Pid:69
Hmm this shows that percpu_counter_tree_precise_sum() is returning 0 but
percpu_counter_tree_approximate_sum() is off more than
counter->inaccuracy. I have not dig deeper to find why but this needs to
be resolved before considering this series for upstream.
I notice that those BUG show up while loading modules at boot in kworker
context, e.g.:
[ 14.858862][ T67] BUG: Bad rss-counter state mm:ffff8881000655c0
type:MM_ANONPAGES val:0 Comm:kworker/u9:0 Pid:67
[ 14.894890][ T69] BUG: Bad rss-counter state mm:ffff888100061cc0
type:MM_FILEPAGES val:0 Comm:kworker/u9:0 Pid:69
[ 14.896108][ T69] BUG: Bad rss-counter state mm:ffff888100061cc0
type:MM_ANONPAGES val:0 Comm:kworker/u9:0 Pid:69
[ 14.918858][ T71] module: module-autoload: duplicate request for
module crypto-aes
[ 14.919479][ T71] module: module-autoload: duplicate request for
module crypto-aes-all
[ 14.920801][ T1] krb5: Running aes128-cts-hmac-sha256-128 enc
plain<block
[ 14.921844][ T1] krb5: Running aes128-cts-hmac-sha256-128 enc
plain==block
[ 14.922852][ T1] krb5: Running aes128-cts-hmac-sha256-128 enc
plain>block
[ 14.923843][ T1] krb5: Running aes256-cts-hmac-sha384-192 enc no
plain
[ 14.939591][ T1] krb5: Running aes256-cts-hmac-sha384-192 enc
plain<block
[ 14.940614][ T1] krb5: Running aes256-cts-hmac-sha384-192 enc
plain==block
[ 14.941586][ T1] krb5: Running aes256-cts-hmac-sha384-192 enc
plain>block
[ 14.942547][ T1] krb5: Running camellia128-cts-cmac enc no plain
[ 15.018568][ T85] BUG: Bad rss-counter state mm:ffff888160f81340
type:MM_ANONPAGES val:0 Comm:kworker/u9:0 Pid:85b
I used "module_init" similarly to lib/percpu_counter.c, but I think it
happens too late in the boot sequence:
module_init(percpu_counter_startup);
module_init maps to __initcall within a built-in compile unit, which
maps to device_initcall(), which happens quite late within the sequence
called from do_initcalls(), called from do_basic_setup().
And even do_basic_setup is documented as:
* Ok, the machine is now initialized. None of the devices
* have been touched yet, but the CPU subsystem is up and
* running, and memory and process management works.
which clearly requires that the mm subsystem is expected to
be ready at that point.
It probably was not an issue for the non-hierarchical percpu
counters because all it was initializing is handling of CPU hotplug,
but the new hierarchical counters initialize the pre-calculated
inaccuracy value which is used to figure out whether the approximate
sum is sufficient to compare values or if the precise sum is needed.
I think this is why we are hitting this BUG.
Now I wonder where I should move this initialization. It requires
"nr_cpu_ids" to be initialized, and pretty much need to be done
before mms are created. I'm starting to suspect that the module init
code can spawn kworkers that have a mm before the init process runs.
At least on x86, nr_cpu_ids appears to be set by set_nr_cpu_ids()
through early_param("possible_cpus", setup_possible_cpus), which is
AFAIU called from parse_early_param(), which happens very early in the
boot sequence.
It would make sense to call an explicit percpu counter tree init
function from start_kernel() between the call to mm_core_init() and the
call to maple_tree_init(). This way it would be initialized right after
mm, but given that the hierarchical counter tree is a lib that can be
used for other purposes than mm accounting, I think it makes sense
to call its init explicitly from start_kernel() rather than bury
it within mm_core_init().
Thoughts ?
Thanks,
Mathieu
--
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com
