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Message-ID: <70dfbac1-4c84-9567-30be-1e2594157e62@bytedance.com>
Date: Tue, 8 Nov 2022 16:58:04 +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 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?
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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