[Devel] [PATCH v3 RH9] cgroup_freezer: print information about unfreezable process

[nb]

On 7.12.22 г. 14:27 ч., nb wrote:
> 
> 
> On 30.11.22 г. 13:22 ч., Pavel Tikhomirov wrote:
>> Add a sysctl kernel.freeze_cgroup_timeout (default value 30 * HZ).
>>
>> If one writes FROZEN to freezer.state file and after a timeout of
>> kernel.freeze_cgroup_timeout one still reads FREEZING from freezer.state
>> file (meaning that kernel does not succeed to freeze cgroup processes
>> still) - let's print a warning with information about the problem, e.g.:
>>
>> [ 7196.621368] Freeze of /test took 0 sec, due to unfreezable process 
>> 13732:bash, stack:
>> [ 7196.621396] [<ffffffffa2df9556>] retint_careful+0x14/0x32
>> [ 7196.621431] [<ffffffffffffffff>] 0xffffffffffffffff
>>
>> The output includes:
>> - path to problematic freezer cgroup
>> - timeout in seconds
>> - unfeezable process pid, comm and stack
>>
>> https://jira.sw.ru/browse/PSBM-142970
>>
>> Signed-off-by: Pavel Tikhomirov <ptikhomirov at virtuozzo.com>
>> ---
>> v3: use kmalloc for entries and freezer_cg_name + reformat
>> ---
>>   include/linux/sysctl.h         |  2 +
>>   kernel/cgroup/legacy_freezer.c | 71 ++++++++++++++++++++++++++++++++--
>>   kernel/sysctl.c                | 10 +++++
>>   3 files changed, 80 insertions(+), 3 deletions(-)
>>
>> diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
>> index 8fd2d3c217c2..b641dd2bba82 100644
>> --- a/include/linux/sysctl.h
>> +++ b/include/linux/sysctl.h
>> @@ -188,6 +188,8 @@ struct ctl_path {
>>   };
>>   extern int trusted_exec;
>> +#define DEFAULT_FREEZE_TIMEOUT (30 * HZ)
>> +extern int sysctl_freeze_timeout;
>>   extern int ve_allow_module_load;
>> diff --git a/kernel/cgroup/legacy_freezer.c 
>> b/kernel/cgroup/legacy_freezer.c
>> index 08236798d173..eea2f0b924f1 100644
>> --- a/kernel/cgroup/legacy_freezer.c
>> +++ b/kernel/cgroup/legacy_freezer.c
>> @@ -22,6 +22,10 @@
>>   #include <linux/freezer.h>
>>   #include <linux/seq_file.h>
>>   #include <linux/mutex.h>
>> +#include <linux/jiffies.h>
>> +#include <linux/ratelimit.h>
>> +#include <linux/stacktrace.h>
>> +#include <linux/sysctl.h>
>>   /*
>>    * A cgroup is freezing if any FREEZING flags are set.  
>> FREEZING_SELF is
>> @@ -43,6 +47,7 @@ enum freezer_state_flags {
>>   struct freezer {
>>       struct cgroup_subsys_state    css;
>>       unsigned int            state;
>> +    unsigned long            freeze_jiffies;
>>   };
>>   static DEFINE_MUTEX(freezer_mutex);
>> @@ -225,6 +230,60 @@ static void freezer_fork(struct task_struct *task)
>>       mutex_unlock(&freezer_mutex);
>>   }
>> +#define MAX_STACK_TRACE_DEPTH   64
>> +
>> +static void check_freezer_timeout(struct cgroup_subsys_state *css,
>> +                  struct task_struct *task)
>> +
>> +{
>> +    static DEFINE_RATELIMIT_STATE(freeze_timeout_rs,
>> +                      DEFAULT_FREEZE_TIMEOUT, 1);
>> +    int __freeze_timeout = READ_ONCE(sysctl_freeze_timeout);
>> +    struct freezer *freezer = css_freezer(css);
>> +    unsigned long nr_entries;
>> +    unsigned long *entries;
>> +    char *freezer_cg_name;
>> +    pid_t tgid;
>> +    int i;
>> +
>> +    if (!freezer->freeze_jiffies ||
>> +        freezer->freeze_jiffies + __freeze_timeout > get_jiffies_64())
>> +        return;
> 
> Don't you want to execute the logic if freeze_jiffies + __freeze_timeout 
> is larger than get_jiffies_64() ? Because this means the timeout has 
> elapsed and you consider the freezer hung?

Ok, disregard it, the code is indeed correct.

> 
> <snip>
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