From 97c2c9b84d0c1edf4926b13661d5af3f0edccbce Mon Sep 17 00:00:00 2001 From: Andrew Morton Date: Tue, 18 Apr 2006 22:20:38 -0700 Subject: [PATCH] oom-kill: mm locking fix Dave Peterson points out that badness() is playing with mm_structs without taking a reference on them. mmput() can sleep, so taking a reference here (inside tasklist_lock) is hard. Fix it up via task_lock() instead. Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/oom_kill.c | 26 ++++++++++++++++++-------- 1 file changed, 18 insertions(+), 8 deletions(-) (limited to 'mm/oom_kill.c') diff --git a/mm/oom_kill.c b/mm/oom_kill.c index 78747afad6b..9a643c4bf77 100644 --- a/mm/oom_kill.c +++ b/mm/oom_kill.c @@ -46,15 +46,25 @@ unsigned long badness(struct task_struct *p, unsigned long uptime) { unsigned long points, cpu_time, run_time, s; - struct list_head *tsk; + struct mm_struct *mm; + struct task_struct *child; - if (!p->mm) + task_lock(p); + mm = p->mm; + if (!mm) { + task_unlock(p); return 0; + } /* * The memory size of the process is the basis for the badness. */ - points = p->mm->total_vm; + points = mm->total_vm; + + /* + * After this unlock we can no longer dereference local variable `mm' + */ + task_unlock(p); /* * Processes which fork a lot of child processes are likely @@ -64,11 +74,11 @@ unsigned long badness(struct task_struct *p, unsigned long uptime) * child is eating the vast majority of memory, adding only half * to the parents will make the child our kill candidate of choice. */ - list_for_each(tsk, &p->children) { - struct task_struct *chld; - chld = list_entry(tsk, struct task_struct, sibling); - if (chld->mm != p->mm && chld->mm) - points += chld->mm->total_vm/2 + 1; + list_for_each_entry(child, &p->children, sibling) { + task_lock(child); + if (child->mm != mm && child->mm) + points += child->mm->total_vm/2 + 1; + task_unlock(child); } /* -- cgit From 013159227b840dfd441bd2e4c8b4d77ffb3cc42e Mon Sep 17 00:00:00 2001 From: Dave Peterson Date: Tue, 18 Apr 2006 22:20:44 -0700 Subject: [PATCH] mm: fix mm_struct reference counting bugs in mm/oom_kill.c Fix oom_kill_task() so it doesn't call mmput() (which may sleep) while holding tasklist_lock. Signed-off-by: David S. Peterson Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/oom_kill.c | 45 +++++++++++++++++++++++---------------------- 1 file changed, 23 insertions(+), 22 deletions(-) (limited to 'mm/oom_kill.c') diff --git a/mm/oom_kill.c b/mm/oom_kill.c index 9a643c4bf77..042e6436c3e 100644 --- a/mm/oom_kill.c +++ b/mm/oom_kill.c @@ -254,17 +254,24 @@ static void __oom_kill_task(task_t *p, const char *message) force_sig(SIGKILL, p); } -static struct mm_struct *oom_kill_task(task_t *p, const char *message) +static int oom_kill_task(task_t *p, const char *message) { - struct mm_struct *mm = get_task_mm(p); + struct mm_struct *mm; task_t * g, * q; - if (!mm) - return NULL; - if (mm == &init_mm) { - mmput(mm); - return NULL; - } + mm = p->mm; + + /* WARNING: mm may not be dereferenced since we did not obtain its + * value from get_task_mm(p). This is OK since all we need to do is + * compare mm to q->mm below. + * + * Furthermore, even if mm contains a non-NULL value, p->mm may + * change to NULL at any time since we do not hold task_lock(p). + * However, this is of no concern to us. + */ + + if (mm == NULL || mm == &init_mm) + return 1; __oom_kill_task(p, message); /* @@ -276,13 +283,12 @@ static struct mm_struct *oom_kill_task(task_t *p, const char *message) __oom_kill_task(q, message); while_each_thread(g, q); - return mm; + return 0; } -static struct mm_struct *oom_kill_process(struct task_struct *p, - unsigned long points, const char *message) +static int oom_kill_process(struct task_struct *p, unsigned long points, + const char *message) { - struct mm_struct *mm; struct task_struct *c; struct list_head *tsk; @@ -293,9 +299,8 @@ static struct mm_struct *oom_kill_process(struct task_struct *p, c = list_entry(tsk, struct task_struct, sibling); if (c->mm == p->mm) continue; - mm = oom_kill_task(c, message); - if (mm) - return mm; + if (!oom_kill_task(c, message)) + return 0; } return oom_kill_task(p, message); } @@ -310,7 +315,6 @@ static struct mm_struct *oom_kill_process(struct task_struct *p, */ void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask, int order) { - struct mm_struct *mm = NULL; task_t *p; unsigned long points = 0; @@ -330,12 +334,12 @@ void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask, int order) */ switch (constrained_alloc(zonelist, gfp_mask)) { case CONSTRAINT_MEMORY_POLICY: - mm = oom_kill_process(current, points, + oom_kill_process(current, points, "No available memory (MPOL_BIND)"); break; case CONSTRAINT_CPUSET: - mm = oom_kill_process(current, points, + oom_kill_process(current, points, "No available memory in cpuset"); break; @@ -357,8 +361,7 @@ retry: panic("Out of memory and no killable processes...\n"); } - mm = oom_kill_process(p, points, "Out of memory"); - if (!mm) + if (oom_kill_process(p, points, "Out of memory")) goto retry; break; @@ -367,8 +370,6 @@ retry: out: read_unlock(&tasklist_lock); cpuset_unlock(); - if (mm) - mmput(mm); /* * Give "p" a good chance of killing itself before we -- cgit