Commit 2ad654bc authored by Zefan Li's avatar Zefan Li Committed by Tejun Heo
Browse files

cpuset: PF_SPREAD_PAGE and PF_SPREAD_SLAB should be atomic flags 

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 happened
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_SPREAD_SLAB atomic flags.

v4:
- updated mm/slab.c. (Fengguang Wu)
- updated Documentation.

Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Miao Xie <miaox@cn.fujitsu.com>
Cc: Kees Cook <keescook@chromium.org>
Fixes: 950592f7 ("cpusets: update tasks' page/slab spread flags in time")
Cc: <stable@vger.kernel.org> # 2.6.31+
Reported-by: default avatarTetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: default avatarZefan Li <lizefan@huawei.com>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent e0e5070b

Documentation/cgroups/cpusets.txt

+3 −3
Original line number Diff line number Diff line
@@ -345,14 +345,14 @@ the named feature on. 
The implementation is simple.



Setting the flag 'cpuset.memory_spread_page' turns on a per-process flag

PF_SPREAD_PAGE for each task that is in that cpuset or subsequently

PFA_SPREAD_PAGE for each task that is in that cpuset or subsequently

joins that cpuset.  The page allocation calls for the page cache

is modified to perform an inline check for this PF_SPREAD_PAGE task

is modified to perform an inline check for this PFA_SPREAD_PAGE task

flag, and if set, a call to a new routine cpuset_mem_spread_node()

returns the node to prefer for the allocation.



Similarly, setting 'cpuset.memory_spread_slab' turns on the flag

PF_SPREAD_SLAB, and appropriately marked slab caches will allocate

PFA_SPREAD_SLAB, and appropriately marked slab caches will allocate

pages from the node returned by cpuset_mem_spread_node().



The cpuset_mem_spread_node() routine is also simple.  It uses the

include/linux/cpuset.h

+2 −2
Original line number Diff line number Diff line
@@ -93,12 +93,12 @@ 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);

include/linux/sched.h

+11 −2
Original line number Diff line number Diff line
@@ -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

 */

kernel/cpuset.c

+5 −4
Original line number Diff line number Diff line
@@ -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);

}



/*

mm/slab.c

+2 −2
Original line number Diff line number Diff line
@@ -2994,7 +2994,7 @@ out: 


#ifdef CONFIG_NUMA

/*

 * Try allocating on another node if PF_SPREAD_SLAB is a mempolicy is set.

 * Try allocating on another node if PFA_SPREAD_SLAB is a mempolicy is set.

 *

 * If we are in_interrupt, then process context, including cpusets and

 * mempolicy, may not apply and should not be used for allocation policy.
@@ -3226,7 +3226,7 @@ __do_cache_alloc(struct kmem_cache *cache, gfp_t flags) 
{

	void *objp;



	if (current->mempolicy || unlikely(current->flags & PF_SPREAD_SLAB)) {

	if (current->mempolicy || cpuset_do_slab_mem_spread()) {

		objp = alternate_node_alloc(cache, flags);

		if (objp)

			goto out;

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