From: Michal Hocko <mhocko@suse.com>
To: Suren Baghdasaryan <surenb@google.com>
Cc: akpm@linux-foundation.org, rientjes@google.com,
willy@infradead.org, hannes@cmpxchg.org, guro@fb.com,
riel@surriel.com, minchan@kernel.org, christian@brauner.io,
hch@infradead.org, oleg@redhat.com, david@redhat.com,
jannh@google.com, shakeelb@google.com, luto@kernel.org,
christian.brauner@ubuntu.com, fweimer@redhat.com,
jengelh@inai.de, timmurray@google.com, linux-api@vger.kernel.org,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
kernel-team@android.com
Subject: Re: [PATCH v6 1/2] mm: introduce process_mrelease system call
Date: Thu, 5 Aug 2021 09:10:23 +0200 [thread overview]
Message-ID: <YQuO36AeQUwsAyU1@dhcp22.suse.cz> (raw)
In-Reply-To: <20210804185004.1304692-1-surenb@google.com>
On Wed 04-08-21 11:50:03, Suren Baghdasaryan wrote:
[...]
> +SYSCALL_DEFINE2(process_mrelease, int, pidfd, unsigned int, flags)
> +{
> +#ifdef CONFIG_MMU
> + struct mm_struct *mm = NULL;
> + struct task_struct *task;
> + unsigned int f_flags;
> + struct pid *pid;
> + long ret = 0;
> +
> + if (flags)
> + return -EINVAL;
> +
> + pid = pidfd_get_pid(pidfd, &f_flags);
> + if (IS_ERR(pid))
> + return PTR_ERR(pid);
> +
> + task = get_pid_task(pid, PIDTYPE_PID);
> + if (!task) {
> + ret = -ESRCH;
> + goto put_pid;
> + }
> +
> + /*
> + * If the task is dying and in the process of releasing its memory
> + * then get its mm.
> + */
> + task = find_lock_task_mm(task);
You want a different task_struct because the returned one might be
different from the given one and you already hold a reference which you
do not want to leak
> + if (!task) {
> + ret = -ESRCH;
> + goto put_pid;
> + }
> + if (task_will_free_mem(task) && (task->flags & PF_KTHREAD) == 0) {
> + mm = task->mm;
> + mmget(mm);
> + }
> + task_unlock(task);
> + if (!mm) {
> + ret = -EINVAL;
> + goto put_task;
> + }
> +
> + if (test_bit(MMF_OOM_SKIP, &mm->flags))
> + goto put_mm;
This is too late to check for MMF_OOM_SKIP. task_will_free_mem will fail
with the flag being set. I believe you want something like the
following:
p = find_lock_task_mm(task);
mm = p->mm;
/* The work has been done already */
if (test_bit(MMF_OOM_SKIP, &mm->flags)) {
task_unlock(p);
goto put_task;
}
i
if (!task_will_free_mem(p)) {
task_unlock(p);
goto put_task;
}
mmget(mm);
task_unlock(p);
> +
> + if (mmap_read_lock_killable(mm)) {
> + ret = -EINTR;
> + goto put_mm;
> + }
> + if (!__oom_reap_task_mm(mm))
> + ret = -EAGAIN;
> + mmap_read_unlock(mm);
> +
> +put_mm:
> + mmput(mm);
> +put_task:
> + put_task_struct(task);
> +put_pid:
> + put_pid(pid);
> + return ret;
> +#else
> + return -ENOSYS;
> +#endif /* CONFIG_MMU */
> +}
> --
> 2.32.0.554.ge1b32706d8-goog
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2021-08-05 7:10 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-04 18:50 [PATCH v6 1/2] mm: introduce process_mrelease system call Suren Baghdasaryan
2021-08-04 18:50 ` [PATCH v6 2/2] mm: wire up syscall process_mrelease Suren Baghdasaryan
2021-08-04 18:58 ` [PATCH v6 1/2] mm: introduce process_mrelease system call David Hildenbrand
2021-08-04 22:50 ` Andrew Morton
2021-08-04 22:55 ` Suren Baghdasaryan
2021-08-04 22:59 ` Shakeel Butt
2021-08-05 7:10 ` Michal Hocko [this message]
2021-08-05 15:29 ` Suren Baghdasaryan
2021-08-05 15:31 ` David Hildenbrand
2021-08-05 17:11 ` Suren Baghdasaryan
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