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Date: Tue, 8 Nov 2022 17:45:30 +0800
From: Qi Zheng <zhengqi.arch@...edance.com>
To: Wei Yongjun <weiyongjun1@...wei.com>, dvyukov@...gle.com,
jgg@...dia.com, willy@...radead.org, akinobu.mita@...il.com
Cc: akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
stable@...r.kernel.org
Subject: Re: [PATCH v2] mm: fix unexpected changes to
{failslab|fail_page_alloc}.attr
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@...r.kernel.org
>>>> Fixes: 3f913fc5f974 ("mm: fix missing handler for __GFP_NOWARN")
>>>> Reported-by: Dmitry Vyukov <dvyukov@...gle.com>
>>>> Signed-off-by: Qi Zheng <zhengqi.arch@...edance.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
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