From: Jann Horn <jannh@google.com>
To: Andrew Morton <akpm@linux-foundation.org>,
linux-mm@kvack.org, Eric Biederman <ebiederm@xmission.com>,
Oleg Nesterov <oleg@redhat.com>
Cc: linux-kernel@vger.kernel.org, Will Deacon <will@kernel.org>,
Kees Cook <keescook@chromium.org>, Ingo Molnar <mingo@kernel.org>
Subject: [RFC PATCH 4/6] mm, oom: Use mm_ref()/mm_unref() and avoid mmdrop_async()
Date: Fri, 16 Oct 2020 04:40:17 +0200 [thread overview]
Message-ID: <20201016024019.1882062-5-jannh@google.com> (raw)
In-Reply-To: <20201016024019.1882062-1-jannh@google.com>
The OOM killer uses MMF_OOM_SKIP to avoid running on an mm that has started
__mmput(); it only uses the mmgrab() reference to ensure that the mm_struct
itself stays alive.
This means that we don't need a full mmgrab() reference, which will keep
the pgd (and potentially also some pmd pages) alive and can't be cleaned up
from RCU callback context; we can use an mm_ref() reference instead.
Signed-off-by: Jann Horn <jannh@google.com>
---
kernel/fork.c | 6 +-----
mm/oom_kill.c | 2 +-
2 files changed, 2 insertions(+), 6 deletions(-)
diff --git a/kernel/fork.c b/kernel/fork.c
index fcdd1ace79e4..59c119b03351 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -686,12 +686,8 @@ static inline void free_signal_struct(struct signal_struct *sig)
{
taskstats_tgid_free(sig);
sched_autogroup_exit(sig);
- /*
- * __mmdrop is not safe to call from softirq context on x86 due to
- * pgd_dtor so postpone it to the async context
- */
if (sig->oom_mm)
- mmdrop_async(sig->oom_mm);
+ mm_unref(sig->oom_mm);
kmem_cache_free(signal_cachep, sig);
}
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index e90f25d6385d..12967f54fbcf 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -704,7 +704,7 @@ static void mark_oom_victim(struct task_struct *tsk)
/* oom_mm is bound to the signal struct life time. */
if (!cmpxchg(&tsk->signal->oom_mm, NULL, mm)) {
- mmgrab(tsk->signal->oom_mm);
+ mm_ref(tsk->signal->oom_mm);
set_bit(MMF_OOM_VICTIM, &mm->flags);
}
--
2.29.0.rc1.297.gfa9743e501-goog
next prev parent reply other threads:[~2020-10-16 2:40 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-16 2:40 [RFC PATCH 0/6] mm and ptrace: Track dumpability until task is freed Jann Horn
2020-10-16 2:40 ` [RFC PATCH 1/6] ptrace: Keep mm around after exit_mm() for __ptrace_may_access() Jann Horn
2020-10-16 2:40 ` [RFC PATCH 2/6] refcount: Move refcount_t definition into linux/types.h Jann Horn
2020-10-16 2:40 ` [RFC PATCH 3/6] mm: Add refcount for preserving mm_struct without pgd Jann Horn
2020-10-16 2:40 ` Jann Horn [this message]
2020-10-16 2:40 ` [RFC PATCH 5/6] ptrace: Use mm_ref() for ->exit_mm Jann Horn
2020-10-16 2:40 ` [RFC PATCH 6/6] mm: remove now-unused mmdrop_async() Jann Horn
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