Messages in this thread Patch in this message | | | Date | Mon, 2 Dec 2013 16:24:40 +0100 | From | Oleg Nesterov <> | Subject | [PATCH 2/2] oom_kill: change oom_kill.c to use for_each_thread() |
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1. Change oom_kill.c to use for_each_thread() rather than the racy while_each_thread() which can loop forever if we race with exit.
Note also that most users were buggy even if while_each_thread() was fine, the task can exit even _before_ rcu_read_lock().
Fortunately the new for_each_thread() only requires the stable task_struct, so this change fixes both problems.
2. At least out_of_memory() calls has_intersects_mems_allowed() without even rcu_read_lock(), this is obviously buggy.
Add the necessary rcu_read_lock(). This means that we can not simply return from the loop, we need "bool ret" and "break".
Signed-off-by: Oleg Nesterov <oleg@redhat.com> --- mm/oom_kill.c | 37 ++++++++++++++++++++----------------- 1 files changed, 20 insertions(+), 17 deletions(-)
diff --git a/mm/oom_kill.c b/mm/oom_kill.c index 1e4a600..47dd4ce 100644 --- a/mm/oom_kill.c +++ b/mm/oom_kill.c @@ -54,12 +54,14 @@ static DEFINE_SPINLOCK(zone_scan_lock); * shares the same mempolicy nodes as current if it is bound by such a policy * and whether or not it has the same set of allowed cpuset nodes. */ -static bool has_intersects_mems_allowed(struct task_struct *tsk, +static bool has_intersects_mems_allowed(struct task_struct *start, const nodemask_t *mask) { - struct task_struct *start = tsk; + struct task_struct *tsk; + bool ret = false; - do { + rcu_read_lock(); + for_each_thread(start, tsk) { if (mask) { /* * If this is a mempolicy constrained oom, tsk's @@ -67,19 +69,20 @@ static bool has_intersects_mems_allowed(struct task_struct *tsk, * mempolicy intersects current, otherwise it may be * needlessly killed. */ - if (mempolicy_nodemask_intersects(tsk, mask)) - return true; + ret = mempolicy_nodemask_intersects(tsk, mask); } else { /* * This is not a mempolicy constrained oom, so only * check the mems of tsk's cpuset. */ - if (cpuset_mems_allowed_intersects(current, tsk)) - return true; + ret = cpuset_mems_allowed_intersects(current, tsk); } - } while_each_thread(start, tsk); + if (ret) + break; + } + rcu_read_unlock(); - return false; + return ret; } #else static bool has_intersects_mems_allowed(struct task_struct *tsk, @@ -97,14 +100,14 @@ static bool has_intersects_mems_allowed(struct task_struct *tsk, */ struct task_struct *find_lock_task_mm(struct task_struct *p) { - struct task_struct *t = p; + struct task_struct *t; - do { + for_each_thread(p, t) { task_lock(t); if (likely(t->mm)) return t; task_unlock(t); - } while_each_thread(p, t); + } return NULL; } @@ -301,7 +304,7 @@ static struct task_struct *select_bad_process(unsigned int *ppoints, unsigned long chosen_points = 0; rcu_read_lock(); - do_each_thread(g, p) { + for_each_process_thread(g, p) { unsigned int points; switch (oom_scan_process_thread(p, totalpages, nodemask, @@ -323,7 +326,7 @@ static struct task_struct *select_bad_process(unsigned int *ppoints, chosen = p; chosen_points = points; } - } while_each_thread(g, p); + } if (chosen) get_task_struct(chosen); rcu_read_unlock(); @@ -406,7 +409,7 @@ void oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order, { struct task_struct *victim = p; struct task_struct *child; - struct task_struct *t = p; + struct task_struct *t; struct mm_struct *mm; unsigned int victim_points = 0; static DEFINE_RATELIMIT_STATE(oom_rs, DEFAULT_RATELIMIT_INTERVAL, @@ -437,7 +440,7 @@ void oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order, * still freeing memory. */ read_lock(&tasklist_lock); - do { + for_each_thread(p, t) { list_for_each_entry(child, &t->children, sibling) { unsigned int child_points; @@ -455,7 +458,7 @@ void oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order, get_task_struct(victim); } } - } while_each_thread(p, t); + } read_unlock(&tasklist_lock); rcu_read_lock(); -- 1.5.5.1
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