The patch titled
oom: introduce find_lock_task_mm() to fix !mm false positives
has been added to the -mm tree. Its filename is
oom-introduce-find_lock_task_mm-to-fix-mm-false-positives.patch
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------------------------------------------------------
Subject: oom: introduce find_lock_task_mm() to fix !mm false positives
From: Oleg Nesterov <oleg@xxxxxxxxxx>
Almost all ->mm == NUL checks in oom_kill.c are wrong.
The current code assumes that the task without ->mm has already
released its memory and ignores the process. However this is not
necessarily true when this process is multithreaded, other live
sub-threads can use this ->mm.
- Remove the "if (!p->mm)" check in select_bad_process(), it is
just wrong.
- Add the new helper, find_lock_task_mm(), which finds the live
thread which uses the memory and takes task_lock() to pin ->mm
- change oom_badness() to use this helper instead of just checking
->mm != NULL.
- As David pointed out, select_bad_process() must never choose the
task without ->mm, but no matter what oom_badness() returns the
task can be chosen if nothing else has been found yet.
Change oom_badness() to return int, change it to return -1 if
find_lock_task_mm() fails, and change select_bad_process() to
check points >= 0.
Note! This patch is not enough, we need more changes.
- oom_badness() was fixed, but oom_kill_task() still ignores
the task without ->mm
- oom_forkbomb_penalty() should use find_lock_task_mm() too,
and it also needs other changes to actually find the first
first-descendant children
This will be addressed later.
Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/oom.h | 2 +-
mm/oom_kill.c | 39 +++++++++++++++++++++------------------
2 files changed, 22 insertions(+), 19 deletions(-)
diff -puN include/linux/oom.h~oom-introduce-find_lock_task_mm-to-fix-mm-false-positives include/linux/oom.h
--- a/include/linux/oom.h~oom-introduce-find_lock_task_mm-to-fix-mm-false-positives
+++ a/include/linux/oom.h
@@ -40,7 +40,7 @@ enum oom_constraint {
CONSTRAINT_MEMORY_POLICY,
};
-extern unsigned int oom_badness(struct task_struct *p,
+extern int oom_badness(struct task_struct *p,
unsigned long totalpages, unsigned long uptime);
extern int try_set_zone_oom(struct zonelist *zonelist, gfp_t gfp_flags);
extern void clear_zonelist_oom(struct zonelist *zonelist, gfp_t gfp_flags);
diff -puN mm/oom_kill.c~oom-introduce-find_lock_task_mm-to-fix-mm-false-positives mm/oom_kill.c
--- a/mm/oom_kill.c~oom-introduce-find_lock_task_mm-to-fix-mm-false-positives
+++ a/mm/oom_kill.c
@@ -70,6 +70,19 @@ static bool has_intersects_mems_allowed(
return false;
}
+static struct task_struct *find_lock_task_mm(struct task_struct *p)
+{
+ struct task_struct *t = p;
+ do {
+ task_lock(t);
+ if (likely(t->mm))
+ return t;
+ task_unlock(t);
+ } while_each_thread(p, t);
+
+ return NULL;
+}
+
/*
* Tasks that fork a very large number of children with seperate address spaces
* may be the result of a bug, user error, malicious applications, or even those
@@ -140,10 +153,9 @@ static unsigned long oom_forkbomb_penalt
* predictable as possible. The goal is to return the highest value for the
* task consuming the most memory to avoid subsequent oom conditions.
*/
-unsigned int oom_badness(struct task_struct *p, unsigned long totalpages,
+int oom_badness(struct task_struct *p, unsigned long totalpages,
unsigned long uptime)
{
- struct mm_struct *mm;
int points;
/*
@@ -160,19 +172,15 @@ unsigned int oom_badness(struct task_str
if (p->flags & PF_OOM_ORIGIN)
return 1000;
- task_lock(p);
- mm = p->mm;
- if (!mm) {
- task_unlock(p);
- return 0;
- }
-
+ p = find_lock_task_mm(p);
+ if (!p)
+ return -1;
/*
* The baseline for the badness score is the proportion of RAM that each
* task's rss and swap space use.
*/
- points = (get_mm_rss(mm) + get_mm_counter(mm, MM_SWAPENTS)) * 1000 /
- totalpages;
+ points = (get_mm_rss(p->mm) + get_mm_counter(p->mm, MM_SWAPENTS)) *
+ 1000 / totalpages;
task_unlock(p);
points += oom_forkbomb_penalty(p);
@@ -289,7 +297,7 @@ static struct task_struct *select_bad_pr
do_posix_clock_monotonic_gettime(&uptime);
for_each_process(p) {
- unsigned int points;
+ int points;
/* skip the init task and kthreads */
if (is_global_init(p) || (p->flags & PF_KTHREAD))
@@ -331,16 +339,11 @@ static struct task_struct *select_bad_pr
*ppoints = 1000;
}
- /*
- * skip the tasks which have already released their mm.
- */
- if (!p->mm)
- continue;
if (p->signal->oom_score_adj == OOM_SCORE_ADJ_MIN)
continue;
points = oom_badness(p, totalpages, uptime.tv_sec);
- if (points > *ppoints || !chosen) {
+ if (points >= 0 && (points > *ppoints || !chosen)) {
chosen = p;
*ppoints = points;
}
_
Patches currently in -mm which might be from oleg@xxxxxxxxxx are
origin.patch
linux-next.patch
cpu-timers-simplify-rlimit_cpu-handling.patch
cpu-timers-cleanup-arm_timer.patch
cpu-timers-return-correct-previous-timer-reload-value.patch
cpu-timers-change-sigev_none-timer-implementation.patch
cpu-timers-assure-to-not-iterate-over-all-threads-in-fastpath_timer_check.patch
cpu-timers-optimize-run_posix_cpu_timers.patch
oom-select_bad_process-check-pf_kthread-instead-of-mm-to-skip-kthreads.patch
oom-select_bad_process-pf_exiting-check-should-take-mm-into-account.patch
oom-introduce-find_lock_task_mm-to-fix-mm-false-positives.patch
oom-oom_forkbomb_penalty-move-thread_group_cputime-out-of-task_lock.patch
kmod-add-init-function-to-usermodehelper.patch
exec-replace-call_usermodehelper_pipe-with-use-of-umh-init-function-and-resolve-limit.patch
umh-creds-convert-call_usermodehelper_keys-to-use-subprocess_info-init.patch
umh-creds-kill-subprocess_info-cred-logic.patch
call_usermodehelper-no-need-to-unblock-signals.patch
wait_for_helper-sigchld-from-user-space-can-lead-to-use-after-free.patch
call_usermodehelper-simplify-fix-umh_no_wait-case.patch
call_usermodehelper-umh_wait_exec-ignores-kernel_thread-failure.patch
coredump-factor-out-the-not-ispipe-file-checks.patch
coredump-cleanup-ispipe-code.patch
coredump-factor-out-put_cred-calls.patch
coredump-shift-down_writemmap_sem-into-coredump_wait.patch
exit-exit_notify-can-trust-signal-notify_count-0.patch
exit-change-zap_other_threads-to-count-sub-threads.patch
exit-avoid-sig-count-in-de_thread-__exit_signal-synchronization.patch
exit-avoid-sig-count-in-__exit_signal-to-detect-the-group-dead-case.patch
posix-cpu-timers-avoid-task-signal-=-null-checks.patch
ia64-ptrace_attach_sync_user_rbs-avoid-task-signal-=-null-checks.patch
fork-exit-move-tty_kref_put-outside-of-__cleanup_signal.patch
signals-make-task_struct-signal-immutable-refcountable.patch
signals-clear-signal-tty-when-the-last-thread-exits.patch
signals-clear-signal-tty-when-the-last-thread-exits-fix.patch
signals-kill-the-awful-task_rq_unlock_wait-hack.patch
exit-__exit_signal-use-thread_group_leader-consistently.patch
kill-the-obsolete-thread_group_cputime_free-and-taskstats_tgid_init-helpers.patch
exit-move-taskstats_tgid_free-from-__exit_signal-to-free_signal_struct.patch
check_unshare_flags-kill-the-bogus-clone_sighand-sig-count-check.patch
proc-get_nr_threads-doesnt-need-siglock-any-longer.patch
proc-make-collect_sigign_sigcatch-rcu-safe.patch
proc-make-task_sig-lockless.patch
proc_sched_show_task-use-get_nr_threads.patch
keyctl_session_to_parent-use-thread_group_empty-to-check-singlethreadness.patch
proc-turn-signal_struct-count-into-int-nr_threads.patch
proc-turn-signal_struct-count-into-int-nr_threads-checkpatch-fixes.patch
proc-cleanup-remove-unused-assignments.patch
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