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Message-ID: <70dfbac1-4c84-9567-30be-1e2594157e62@bytedance.com>
Date:   Tue, 8 Nov 2022 16:58:04 +0800
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Subject: Re: [PATCH v2] mm: fix unexpected changes to
 {failslab|fail_page_alloc}.attr
Content-Language: en-US
To:     Wei Yongjun <weiyongjun1@huawei.com>, dvyukov@google.com,
        jgg@nvidia.com, willy@infradead.org, akinobu.mita@gmail.com
Cc:     akpm@linux-foundation.org, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, linux-fsdevel@vger.kernel.org,
        stable@vger.kernel.org
References: <Y2kxrerISWIxQsFO@nvidia.com>
 <20221108035232.87180-1-zhengqi.arch@bytedance.com>
 <65863340-b32f-a2fe-67ae-f1079b19eee4@huawei.com>
From:   Qi Zheng <zhengqi.arch@bytedance.com>
In-Reply-To: <65863340-b32f-a2fe-67ae-f1079b19eee4@huawei.com>
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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@vger.kernel.org
>> Fixes: 3f913fc5f974 ("mm: fix missing handler for __GFP_NOWARN")
>> Reported-by: Dmitry Vyukov <dvyukov@google.com>
>> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
>> ---
>>   v1: https://lore.kernel.org/lkml/20221107033109.59709-1-zhengqi.arch@bytedance.com/
>>
>>   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?

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

-- 
Thanks,
Qi