Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <ab916d48-16cb-8d22-1006-a2906a6296ea@bytedance.com>
Date:   Tue, 8 Nov 2022 17:45:30 +0800
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:102.0)
 Gecko/20100101 Thunderbird/102.3.3
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>
 <70dfbac1-4c84-9567-30be-1e2594157e62@bytedance.com>
 <e644e4bf-f1e0-3e22-7773-62f38f9b8963@huawei.com>
From:   Qi Zheng <zhengqi.arch@bytedance.com>
In-Reply-To: <e644e4bf-f1e0-3e22-7773-62f38f9b8963@huawei.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 8bit
Precedence: bulk


On 2022/11/8 17:32, Wei Yongjun wrote:
> 
> 
> 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@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?
> 
> Yes, just like:
> 
> echo 1 > /sys/kernel/debug/failslab/no_warn  #disable message
> echo 0 > /sys/kernel/debug/failslab/no_warn  #enable message

Got it. Let's wait for the other people's comments and suggestions. :)

> 
> 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
>>

-- 
Thanks,
Qi