From 047200481e7f98e6334d751010c9470efb531b71 Mon Sep 17 00:00:00 2001 From: Michal Hocko Date: Fri, 20 May 2016 16:57:21 -0700 Subject: [PATCH] BACKPORT: partial: mm, oom_reaper: do not mmput synchronously from the oom reaper context MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit (cherry picked from commit ec8d7c14ea14922fe21945b458a75e39f11dd832) Tetsuo has properly noted that mmput slow path might get blocked waiting for another party (e.g. exit_aio waits for an IO). If that happens the oom_reaper would be put out of the way and will not be able to process next oom victim. We should strive for making this context as reliable and independent on other subsystems as much as possible. Introduce mmput_async which will perform the slow path from an async (WQ) context. This will delay the operation but that shouldn't be a problem because the oom_reaper has reclaimed the victim's address space for most cases as much as possible and the remaining context shouldn't bind too much memory anymore. The only exception is when mmap_sem trylock has failed which shouldn't happen too often. The issue is only theoretical but not impossible. Signed-off-by: Michal Hocko Reported-by: Tetsuo Handa Cc: David Rientjes Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Only backports mmput_async. Change-Id: I5fe54abcc629e7d9eab9fe03908903d1174177f1 Signed-off-by: Arve Hjønnevåg --- include/linux/mm_types.h | 2 ++ include/linux/sched.h | 5 ++++ kernel/fork.c | 52 +++++++++++++++++++++++++++------------- 3 files changed, 43 insertions(+), 16 deletions(-) diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index b32cb7add09c..907f94428ccc 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -12,6 +12,7 @@ #include #include #include +#include #include #include @@ -523,6 +524,7 @@ struct mm_struct { #ifdef CONFIG_HUGETLB_PAGE atomic_long_t hugetlb_usage; #endif + struct work_struct async_put_work; }; static inline void mm_init_cpumask(struct mm_struct *mm) diff --git a/include/linux/sched.h b/include/linux/sched.h index a6800fb3f4ea..d0d0b1b45418 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -2764,6 +2764,11 @@ static inline void mmdrop(struct mm_struct * mm) /* mmput gets rid of the mappings and all user-space */ extern void mmput(struct mm_struct *); +/* same as above but performs the slow path from the async kontext. Can + * be called from the atomic context as well + */ +extern void mmput_async(struct mm_struct *); + /* Grab a reference to a task's mm, if it is not already going away */ extern struct mm_struct *get_task_mm(struct task_struct *task); /* diff --git a/kernel/fork.c b/kernel/fork.c index f98b3360397c..2633d5f61d3c 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -695,6 +695,26 @@ void __mmdrop(struct mm_struct *mm) } EXPORT_SYMBOL_GPL(__mmdrop); +static inline void __mmput(struct mm_struct *mm) +{ + VM_BUG_ON(atomic_read(&mm->mm_users)); + + uprobe_clear_state(mm); + exit_aio(mm); + ksm_exit(mm); + khugepaged_exit(mm); /* must run before exit_mmap */ + exit_mmap(mm); + set_mm_exe_file(mm, NULL); + if (!list_empty(&mm->mmlist)) { + spin_lock(&mmlist_lock); + list_del(&mm->mmlist); + spin_unlock(&mmlist_lock); + } + if (mm->binfmt) + module_put(mm->binfmt->module); + mmdrop(mm); +} + /* * Decrement the use count and release all resources for an mm. */ @@ -702,25 +722,25 @@ void mmput(struct mm_struct *mm) { might_sleep(); - if (atomic_dec_and_test(&mm->mm_users)) { - uprobe_clear_state(mm); - exit_aio(mm); - ksm_exit(mm); - khugepaged_exit(mm); /* must run before exit_mmap */ - exit_mmap(mm); - set_mm_exe_file(mm, NULL); - if (!list_empty(&mm->mmlist)) { - spin_lock(&mmlist_lock); - list_del(&mm->mmlist); - spin_unlock(&mmlist_lock); - } - if (mm->binfmt) - module_put(mm->binfmt->module); - mmdrop(mm); - } + if (atomic_dec_and_test(&mm->mm_users)) + __mmput(mm); } EXPORT_SYMBOL_GPL(mmput); +static void mmput_async_fn(struct work_struct *work) +{ + struct mm_struct *mm = container_of(work, struct mm_struct, async_put_work); + __mmput(mm); +} + +void mmput_async(struct mm_struct *mm) +{ + if (atomic_dec_and_test(&mm->mm_users)) { + INIT_WORK(&mm->async_put_work, mmput_async_fn); + schedule_work(&mm->async_put_work); + } +} + /** * set_mm_exe_file - change a reference to the mm's executable file *