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Date: Wed, 24 Sep 2014 11:15:36 +0800
From: Zefan Li <lizefan@...wei.com>
To: David Rientjes <rientjes@...gle.com>
CC: Tejun Heo <tj@...nel.org>, Peter Zijlstra <peterz@...radead.org>,
"Ingo Molnar" <mingo@...nel.org>,
Kees Cook <keescook@...omium.org>,
Miao Xie <miaox@...fujitsu.com>,
Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
LKML <linux-kernel@...r.kernel.org>,
Cgroups <cgroups@...r.kernel.org>
Subject: Re: [PATCH v3 3/3] cpuset: PF_SPREAD_PAGE and PF_SPREAD_SLAB should
be atomic flags
于 2014/9/24 6:10, David Rientjes wrote:
> On Tue, 23 Sep 2014, Zefan Li wrote:
>
>> When we change cpuset.memory_spread_{page,slab}, cpuset will flip
>> PF_SPREAD_{PAGE,SLAB} bit of tsk->flags for each task in that cpuset.
>> This should be done using atomic bitops, but currently we don't,
>> which is broken.
>>
>> Tetsuo reported a hard-to-reproduce kernel crash on RHEL6, which happend
>> when one thread tried to clear PF_USED_MATH while at the same time another
>> thread tried to flip PF_SPREAD_PAGE/PF_SPREAD_SLAB. They both operate on
>> the same task.
>>
>> Here's the full report:
>> https://lkml.org/lkml/2014/9/19/230
>>
>> To fix this, we make PF_SPREAD_PAGE and PF_SPARED_SLAB atomic flags.
>>
>
> s/SPARED/SPREAD/
>
>> Cc: Peter Zijlstra <peterz@...radead.org>
>> Cc: Ingo Molnar <mingo@...nel.org>
>> Cc: Miao Xie <miaox@...fujitsu.com>
>> Cc: Kees Cook <keescook@...omium.org>
>> Fixes: 950592f7b991 ("cpusets: update tasks' page/slab spread flags in time")
>> Cc: <stable@...r.kernel.org> # 2.6.31+
>> Reported-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
>> Signed-off-by: Zefan Li <lizefan@...wei.com>
>> ---
>> include/linux/cpuset.h | 4 ++--
>> include/linux/sched.h | 13 +++++++++++--
>> kernel/cpuset.c | 9 +++++----
>> 3 files changed, 18 insertions(+), 8 deletions(-)
>>
>> diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
>> index 0d4e067..2f073db 100644
>> --- a/include/linux/cpuset.h
>> +++ b/include/linux/cpuset.h
>> @@ -94,12 +94,12 @@ extern int cpuset_slab_spread_node(void);
>>
>> static inline int cpuset_do_page_mem_spread(void)
>> {
>> - return current->flags & PF_SPREAD_PAGE;
>> + return task_spread_page(current);
>> }
>>
>> static inline int cpuset_do_slab_mem_spread(void)
>> {
>> - return current->flags & PF_SPREAD_SLAB;
>> + return task_spread_slab(current);
>> }
>>
>> extern int current_cpuset_is_being_rebound(void);
>> diff --git a/include/linux/sched.h b/include/linux/sched.h
>> index 5630763..7b1cafe 100644
>> --- a/include/linux/sched.h
>> +++ b/include/linux/sched.h
>> @@ -1903,8 +1903,6 @@ extern void thread_group_cputime_adjusted(struct task_struct *p, cputime_t *ut,
>> #define PF_KTHREAD 0x00200000 /* I am a kernel thread */
>> #define PF_RANDOMIZE 0x00400000 /* randomize virtual address space */
>> #define PF_SWAPWRITE 0x00800000 /* Allowed to write to swap */
>> -#define PF_SPREAD_PAGE 0x01000000 /* Spread page cache over cpuset */
>> -#define PF_SPREAD_SLAB 0x02000000 /* Spread some slab caches over cpuset */
>> #define PF_NO_SETAFFINITY 0x04000000 /* Userland is not allowed to meddle with cpus_allowed */
>> #define PF_MCE_EARLY 0x08000000 /* Early kill for mce process policy */
>> #define PF_MUTEX_TESTER 0x20000000 /* Thread belongs to the rt mutex tester */
>> @@ -1958,6 +1956,9 @@ static inline void memalloc_noio_restore(unsigned int flags)
>>
>> /* Per-process atomic flags. */
>> #define PFA_NO_NEW_PRIVS 0 /* May not gain new privileges. */
>> +#define PFA_SPREAD_PAGE 1 /* Spread page cache over cpuset */
>> +#define PFA_SPREAD_SLAB 2 /* Spread some slab caches over cpuset */
>> +
>>
>> #define TASK_PFA_TEST(name, func) \
>> static inline bool task_##func(struct task_struct *p) \
>> @@ -1972,6 +1973,14 @@ static inline void memalloc_noio_restore(unsigned int flags)
>> TASK_PFA_TEST(NO_NEW_PRIVS, no_new_privs)
>> TASK_PFA_SET(NO_NEW_PRIVS, no_new_privs)
>>
>> +TASK_PFA_TEST(SPREAD_PAGE, spread_page)
>> +TASK_PFA_SET(SPREAD_PAGE, spread_page)
>> +TASK_PFA_CLEAR(SPREAD_PAGE, spread_page)
>> +
>> +TASK_PFA_TEST(SPREAD_SLAB, spread_slab)
>> +TASK_PFA_SET(SPREAD_SLAB, spread_slab)
>> +TASK_PFA_CLEAR(SPREAD_SLAB, spread_slab)
>> +
>> /*
>> * task->jobctl flags
>> */
>> diff --git a/kernel/cpuset.c b/kernel/cpuset.c
>> index a37f4ed..1f107c7 100644
>> --- a/kernel/cpuset.c
>> +++ b/kernel/cpuset.c
>> @@ -365,13 +365,14 @@ static void cpuset_update_task_spread_flag(struct cpuset *cs,
>> struct task_struct *tsk)
>> {
>> if (is_spread_page(cs))
>> - tsk->flags |= PF_SPREAD_PAGE;
>> + task_set_spread_page(tsk);
>> else
>> - tsk->flags &= ~PF_SPREAD_PAGE;
>> + task_clear_spread_page(tsk);
>> +
>> if (is_spread_slab(cs))
>> - tsk->flags |= PF_SPREAD_SLAB;
>> + task_set_spread_slab(tsk);
>> else
>> - tsk->flags &= ~PF_SPREAD_SLAB;
>> + task_clear_spread_slab(tsk);
>> }
>>
>> /*
>
> This most certainly needs commentary to specify why these have to be
> atomic ops.
> .
It won't hurt to add more comment, but I don't think it's necessary, because
the reason to use atomic bitops seems obvious to me. Besides there's no such
comment for no_new_privs, which was tsk->atomic_flags introduced for.
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