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Message-ID: <e644e4bf-f1e0-3e22-7773-62f38f9b8963@huawei.com>
Date: Tue, 8 Nov 2022 17:32:52 +0800
From: Wei Yongjun <weiyongjun1@...wei.com>
To: Qi Zheng <zhengqi.arch@...edance.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 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
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
>
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