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 <pet...@infradead.org>
> Cc: Ingo Molnar <mi...@kernel.org>
> Cc: Miao Xie <mi...@cn.fujitsu.com>
> Cc: Kees Cook <keesc...@chromium.org>
> Fixes: 950592f7b991 ("cpusets: update tasks' page/slab spread flags in time")
> Cc: <sta...@vger.kernel.org> # 2.6.31+
> Reported-by: Tetsuo Handa <penguin-ker...@i-love.sakura.ne.jp>
> Signed-off-by: Zefan Li <lize...@huawei.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.
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