Re: [PATCH v2] mm: fix unexpected changes to {failslab|fail_page_alloc}.attr

[Wei Yongjun]

On 2022/11/8 16:58, Qi Zheng wrote:
> 
> 
> On 2022/11/8 16:44, Wei Yongjun wrote:
>> Hi Zheng Qi,
>>
>> On 2022/11/8 11:52, Qi Zheng wrote:
>>> When we specify __GFP_NOWARN, we only expect that no warnings
>>> will be issued for current caller. But in the __should_failslab()
>>> and __should_fail_alloc_page(), the local GFP flags alter the
>>> global {failslab|fail_page_alloc}.attr, which is persistent and
>>> shared by all tasks. This is not what we expected, let's fix it.
>>>
>>> Cc: stable@xxxxxxxxxxxxxxx
>>> Fixes: 3f913fc5f974 ("mm: fix missing handler for __GFP_NOWARN")
>>> Reported-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
>>> Signed-off-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
>>> ---
>>>   v1: https://lore.kernel.org/lkml/20221107033109.59709-1-zhengqi.arch@xxxxxxxxxxxxx/
>>>
>>>   Changelog in v1 -> v2:
>>>    - add comment for __should_failslab() and __should_fail_alloc_page()
>>>      (suggested by Jason)
>>>
>>>   include/linux/fault-inject.h |  7 +++++--
>>>   lib/fault-inject.c           | 14 +++++++++-----
>>>   mm/failslab.c                | 12 ++++++++++--
>>>   mm/page_alloc.c              |  7 +++++--
>>>   4 files changed, 29 insertions(+), 11 deletions(-)
>>>
>>> diff --git a/include/linux/fault-inject.h b/include/linux/fault-inject.h
>>> index 9f6e25467844..444236dadcf0 100644
>>> --- a/include/linux/fault-inject.h
>>> +++ b/include/linux/fault-inject.h
>>> @@ -20,7 +20,6 @@ struct fault_attr {
>>>       atomic_t space;
>>>       unsigned long verbose;
>>>       bool task_filter;
>>> -    bool no_warn;
>>>       unsigned long stacktrace_depth;
>>>       unsigned long require_start;
>>>       unsigned long require_end;
>>> @@ -32,6 +31,10 @@ struct fault_attr {
>>>       struct dentry *dname;
>>>   };
>>>   +enum fault_flags {
>>> +    FAULT_NOWARN =    1 << 0,
>>> +};
>>> +
>>>   #define FAULT_ATTR_INITIALIZER {                    \
>>>           .interval = 1,                        \
>>>           .times = ATOMIC_INIT(1),                \
>>> @@ -40,11 +43,11 @@ struct fault_attr {
>>>           .ratelimit_state = RATELIMIT_STATE_INIT_DISABLED,    \
>>>           .verbose = 2,                        \
>>>           .dname = NULL,                        \
>>> -        .no_warn = false,                    \
>>
>> How about keep no_warn attr as it be, and export it to user?
>>
>> When testing with fault injection, and each fault will print an backtrace.
>> but not all of the testsuit can tell us which one is fault injection
>> message or other is a real warning/crash like syzkaller do.
>>
>> In my case, to make things simple, we usually used a regex to detect whether
>> wanring/error happend. So we disabled the slab/page fault warning message by
>> default, and only enable it when debug real issue.
> 
> So you want to set/clear this no_warn attr through the procfs or sysfs
> interface, so that you can easily disable/enable the slab/page fault
> warning message from the user mode. Right?

Yes, just like:

echo 1 > /sys/kernel/debug/failslab/no_warn  #disable message
echo 0 > /sys/kernel/debug/failslab/no_warn  #enable message

Regards
Wei Yongjun

> 
> Seems reasonable to me. Anyone else has an opinion on this? If it is
> really needed, I can do it later.
> 
> Thanks,
> Qi
> 
>>
>> Regards,
>>
>>
>>>       }
>>>     #define DECLARE_FAULT_ATTR(name) struct fault_attr name = FAULT_ATTR_INITIALIZER
>>>   int setup_fault_attr(struct fault_attr *attr, char *str);
>>> +bool should_fail_ex(struct fault_attr *attr, ssize_t size, int flags);
>>>   bool should_fail(struct fault_attr *attr, ssize_t size);
>>>     #ifdef CONFIG_FAULT_INJECTION_DEBUG_FS
>>> diff --git a/lib/fault-inject.c b/lib/fault-inject.c
>>> index 4b8fafce415c..5971f7c3e49e 100644
>>> --- a/lib/fault-inject.c
>>> +++ b/lib/fault-inject.c
>>> @@ -41,9 +41,6 @@ EXPORT_SYMBOL_GPL(setup_fault_attr);
>>>     static void fail_dump(struct fault_attr *attr)
>>>   {
>>> -    if (attr->no_warn)
>>> -        return;
>>> -
>>>       if (attr->verbose > 0 && __ratelimit(&attr->ratelimit_state)) {
>>>           printk(KERN_NOTICE "FAULT_INJECTION: forcing a failure.\n"
>>>                  "name %pd, interval %lu, probability %lu, "
>>> @@ -103,7 +100,7 @@ static inline bool fail_stacktrace(struct fault_attr *attr)
>>>    * http://www.nongnu.org/failmalloc/
>>>    */
>>>   -bool should_fail(struct fault_attr *attr, ssize_t size)
>>> +bool should_fail_ex(struct fault_attr *attr, ssize_t size, int flags)
>>>   {
>>>       bool stack_checked = false;
>>>   @@ -152,13 +149,20 @@ bool should_fail(struct fault_attr *attr, ssize_t size)
>>>           return false;
>>>     fail:
>>> -    fail_dump(attr);
>>> +    if (!(flags & FAULT_NOWARN))
>>> +        fail_dump(attr);
>>>         if (atomic_read(&attr->times) != -1)
>>>           atomic_dec_not_zero(&attr->times);
>>>         return true;
>>>   }
>>> +EXPORT_SYMBOL_GPL(should_fail_ex);
>>> +
>>> +bool should_fail(struct fault_attr *attr, ssize_t size)
>>> +{
>>> +    return should_fail_ex(attr, size, 0);
>>> +}
>>>   EXPORT_SYMBOL_GPL(should_fail);
>>>     #ifdef CONFIG_FAULT_INJECTION_DEBUG_FS
>>> diff --git a/mm/failslab.c b/mm/failslab.c
>>> index 58df9789f1d2..ffc420c0e767 100644
>>> --- a/mm/failslab.c
>>> +++ b/mm/failslab.c
>>> @@ -16,6 +16,8 @@ static struct {
>>>     bool __should_failslab(struct kmem_cache *s, gfp_t gfpflags)
>>>   {
>>> +    int flags = 0;
>>> +
>>>       /* No fault-injection for bootstrap cache */
>>>       if (unlikely(s == kmem_cache))
>>>           return false;
>>> @@ -30,10 +32,16 @@ bool __should_failslab(struct kmem_cache *s, gfp_t gfpflags)
>>>       if (failslab.cache_filter && !(s->flags & SLAB_FAILSLAB))
>>>           return false;
>>>   +    /*
>>> +     * In some cases, it expects to specify __GFP_NOWARN
>>> +     * to avoid printing any information(not just a warning),
>>> +     * thus avoiding deadlocks. See commit 6b9dbedbe349 for
>>> +     * details.
>>> +     */
>>>       if (gfpflags & __GFP_NOWARN)
>>> -        failslab.attr.no_warn = true;
>>> +        flags |= FAULT_NOWARN;
>>>   -    return should_fail(&failslab.attr, s->object_size);
>>> +    return should_fail_ex(&failslab.attr, s->object_size, flags);
>>>   }
>>>     static int __init setup_failslab(char *str)
>>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>>> index 7192ded44ad0..cb6fe715d983 100644
>>> --- a/mm/page_alloc.c
>>> +++ b/mm/page_alloc.c
>>> @@ -3902,6 +3902,8 @@ __setup("fail_page_alloc=", setup_fail_page_alloc);
>>>     static bool __should_fail_alloc_page(gfp_t gfp_mask, unsigned int order)
>>>   {
>>> +    int flags = 0;
>>> +
>>>       if (order < fail_page_alloc.min_order)
>>>           return false;
>>>       if (gfp_mask & __GFP_NOFAIL)
>>> @@ -3912,10 +3914,11 @@ static bool __should_fail_alloc_page(gfp_t gfp_mask, unsigned int order)
>>>               (gfp_mask & __GFP_DIRECT_RECLAIM))
>>>           return false;
>>>   +    /* See comment in __should_failslab() */
>>>       if (gfp_mask & __GFP_NOWARN)
>>> -        fail_page_alloc.attr.no_warn = true;
>>> +        flags |= FAULT_NOWARN;
>>>   -    return should_fail(&fail_page_alloc.attr, 1 << order);
>>> +    return should_fail_ex(&fail_page_alloc.attr, 1 << order, flags);
>>>   }
>>>     #ifdef CONFIG_FAULT_INJECTION_DEBUG_FS
>