From 40af1bbdca47e5c8a2044039bb78ca8fd8b20f94 Mon Sep 17 00:00:00 2001 From: Konstantin Khlebnikov Date: Thu, 7 Jun 2012 14:21:14 -0700 Subject: mm: correctly synchronize rss-counters at exit/exec mm->rss_stat counters have per-task delta: task->rss_stat. Before changing task->mm pointer the kernel must flush this delta with sync_mm_rss(). do_exit() already calls sync_mm_rss() to flush the rss-counters before committing the rss statistics into task->signal->maxrss, taskstats, audit and other stuff. Unfortunately the kernel does this before calling mm_release(), which can call put_user() for processing task->clear_child_tid. So at this point we can trigger page-faults and task->rss_stat becomes non-zero again. As a result mm->rss_stat becomes inconsistent and check_mm() will print something like this: | BUG: Bad rss-counter state mm:ffff88020813c380 idx:1 val:-1 | BUG: Bad rss-counter state mm:ffff88020813c380 idx:2 val:1 This patch moves sync_mm_rss() into mm_release(), and moves mm_release() out of do_exit() and calls it earlier. After mm_release() there should be no pagefaults. [akpm@linux-foundation.org: tweak comment] Signed-off-by: Konstantin Khlebnikov Reported-by: Markus Trippelsdorf Cc: Hugh Dickins Cc: KAMEZAWA Hiroyuki Cc: Oleg Nesterov Cc: [3.4.x] Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/exec.c | 1 - 1 file changed, 1 deletion(-) (limited to 'fs/exec.c') diff --git a/fs/exec.c b/fs/exec.c index a79786a8d2c8..b926ed19301e 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -819,7 +819,6 @@ static int exec_mmap(struct mm_struct *mm) /* Notify parent that we're no longer interested in the old VM */ tsk = current; old_mm = current->mm; - sync_mm_rss(old_mm); mm_release(tsk, old_mm); if (old_mm) { -- cgit v1.2.3 From 48d212a2eecaca2e1875925837ad27b2f43f48a3 Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Thu, 7 Jun 2012 17:54:07 -0700 Subject: Revert "mm: correctly synchronize rss-counters at exit/exec" This reverts commit 40af1bbdca47e5c8a2044039bb78ca8fd8b20f94. It's horribly and utterly broken for at least the following reasons: - calling sync_mm_rss() from mmput() is fundamentally wrong, because there's absolutely no reason to believe that the task that does the mmput() always does it on its own VM. Example: fork, ptrace, /proc - you name it. - calling it *after* having done mmdrop() on it is doubly insane, since the mm struct may well be gone now. - testing mm against NULL before you call it is insane too, since a NULL mm there would have caused oopses long before. .. and those are just the three bugs I found before I decided to give up looking for me and revert it asap. I should have caught it before I even took it, but I trusted Andrew too much. Cc: Konstantin Khlebnikov Cc: Markus Trippelsdorf Cc: Hugh Dickins Cc: KAMEZAWA Hiroyuki Cc: Oleg Nesterov Cc: Andrew Morton Signed-off-by: Linus Torvalds --- fs/exec.c | 1 + kernel/exit.c | 13 +++++-------- kernel/fork.c | 8 -------- 3 files changed, 6 insertions(+), 16 deletions(-) (limited to 'fs/exec.c') diff --git a/fs/exec.c b/fs/exec.c index b926ed19301e..a79786a8d2c8 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -819,6 +819,7 @@ static int exec_mmap(struct mm_struct *mm) /* Notify parent that we're no longer interested in the old VM */ tsk = current; old_mm = current->mm; + sync_mm_rss(old_mm); mm_release(tsk, old_mm); if (old_mm) { diff --git a/kernel/exit.c b/kernel/exit.c index 804fb6bb8161..34867cc5b42a 100644 --- a/kernel/exit.c +++ b/kernel/exit.c @@ -423,7 +423,6 @@ void daemonize(const char *name, ...) * user space pages. We don't need them, and if we didn't close them * they would be locked into memory. */ - mm_release(current, current->mm); exit_mm(current); /* * We don't want to get frozen, in case system-wide hibernation @@ -641,6 +640,7 @@ static void exit_mm(struct task_struct * tsk) struct mm_struct *mm = tsk->mm; struct core_state *core_state; + mm_release(tsk, mm); if (!mm) return; /* @@ -960,13 +960,9 @@ void do_exit(long code) preempt_count()); acct_update_integrals(tsk); - - /* Set exit_code before complete_vfork_done() in mm_release() */ - tsk->exit_code = code; - - /* Release mm and sync mm's RSS info before statistics gathering */ - mm_release(tsk, tsk->mm); - + /* sync mm's RSS info before statistics gathering */ + if (tsk->mm) + sync_mm_rss(tsk->mm); group_dead = atomic_dec_and_test(&tsk->signal->live); if (group_dead) { hrtimer_cancel(&tsk->signal->real_timer); @@ -979,6 +975,7 @@ void do_exit(long code) tty_audit_exit(); audit_free(tsk); + tsk->exit_code = code; taskstats_exit(tsk, group_dead); exit_mm(tsk); diff --git a/kernel/fork.c b/kernel/fork.c index 0560781c6904..ab5211b9e622 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -619,14 +619,6 @@ void mmput(struct mm_struct *mm) module_put(mm->binfmt->module); mmdrop(mm); } - - /* - * Final rss-counter synchronization. After this point there must be - * no pagefaults into this mm from the current context. Otherwise - * mm->rss_stat will be inconsistent. - */ - if (mm) - sync_mm_rss(mm); } EXPORT_SYMBOL_GPL(mmput); -- cgit v1.2.3 From 4fe7efdbdfb1c7e7a7f31decfd831c0f31d37091 Mon Sep 17 00:00:00 2001 From: Konstantin Khlebnikov Date: Wed, 20 Jun 2012 12:53:01 -0700 Subject: mm: correctly synchronize rss-counters at exit/exec do_exit() and exec_mmap() call sync_mm_rss() before mm_release() does put_user(clear_child_tid) which can update task->rss_stat and thus make mm->rss_stat inconsistent. This triggers the "BUG:" printk in check_mm(). Let's fix this bug in the safest way, and optimize/cleanup this later. Reported-by: Markus Trippelsdorf Signed-off-by: Konstantin Khlebnikov Cc: Oleg Nesterov Cc: KAMEZAWA Hiroyuki Cc: Hugh Dickins Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/exec.c | 2 +- kernel/exit.c | 1 + 2 files changed, 2 insertions(+), 1 deletion(-) (limited to 'fs/exec.c') diff --git a/fs/exec.c b/fs/exec.c index a79786a8d2c8..da27b91ff1e8 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -819,10 +819,10 @@ static int exec_mmap(struct mm_struct *mm) /* Notify parent that we're no longer interested in the old VM */ tsk = current; old_mm = current->mm; - sync_mm_rss(old_mm); mm_release(tsk, old_mm); if (old_mm) { + sync_mm_rss(old_mm); /* * Make sure that if there is a core dump in progress * for the old mm, we get out and die instead of going diff --git a/kernel/exit.c b/kernel/exit.c index 34867cc5b42a..c0277d3f1aaa 100644 --- a/kernel/exit.c +++ b/kernel/exit.c @@ -643,6 +643,7 @@ static void exit_mm(struct task_struct * tsk) mm_release(tsk, mm); if (!mm) return; + sync_mm_rss(mm); /* * Serialize with any possible pending coredump. * We must hold mmap_sem around checking core_state -- cgit v1.2.3