Re: [PATCH v6 1/2] mm: introduce process_mrelease system call
flat view
From: Michal Hocko <mhocko@suse.com>
Date: 2021-08-05 07:10:28
Also in:
linux-mm, lkml
On Wed 04-08-21 11:50:03, Suren Baghdasaryan wrote: [...]
quoted hunk ↗ jump to hunk
+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
quoted hunk ↗ jump to hunk
+ 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