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Fri, 06 Aug 2021 09:07:39 -0700 (PDT) MIME-Version: 1.0 References: <20210805170859.2389276-1-surenb@google.com> In-Reply-To: From: Suren Baghdasaryan Date: Fri, 6 Aug 2021 09:07:28 -0700 Message-ID: Subject: Re: [PATCH v7 1/2] mm: introduce process_mrelease system call To: Michal Hocko Cc: Andrew Morton , David Rientjes , Matthew Wilcox , Johannes Weiner , Roman Gushchin , Rik van Riel , Minchan Kim , Christian Brauner , Christoph Hellwig , Oleg Nesterov , David Hildenbrand , Jann Horn , Shakeel Butt , Andy Lutomirski , Christian Brauner , Florian Weimer , Jan Engelhardt , Tim Murray , Linux API , linux-mm , LKML , kernel-team Content-Type: text/plain; charset="UTF-8" Authentication-Results: imf15.hostedemail.com; dkim=pass header.d=google.com header.s=20161025 header.b=kTUbPF5b; spf=pass (imf15.hostedemail.com: domain of surenb@google.com designates 209.85.219.172 as permitted sender) smtp.mailfrom=surenb@google.com; dmarc=pass (policy=reject) header.from=google.com X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: D4C57D001118 X-Stat-Signature: 55buzekrgtc5b8cme6h1qaydhyh4toew X-HE-Tag: 1628266060-415671 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, Aug 5, 2021 at 11:40 PM Michal Hocko wrote: > > On Thu 05-08-21 10:08:58, Suren Baghdasaryan wrote: > [...] > > + /* > > + * If the task is dying and in the process of releasing its memory > > + * then get its mm. > > + */ > > + p = find_lock_task_mm(task); > > + if (!p) { > > + ret = -ESRCH; > > + goto put_pid; > > + } > > + if (task != p) { > > + get_task_struct(p); > > + put_task_struct(task); > > + task = p; > > + } > > Why do you need to take a reference to the p here? You are under > task_lock so this will not go away and you only need p to get your mm. True. > > > + > > + /* If the work has been done already, just exit with success */ > > + if (test_bit(MMF_OOM_SKIP, &task->mm->flags)) > > + goto put_task; > > You want to release the task_lock Missed it again :( > > > + > > + if (task_will_free_mem(task) && (task->flags & PF_KTHREAD) == 0) { > > you want task_will_free_mem(p) and what is the point of the PF_KTHREAD > check? Yeah, looks like task_will_free_mem() covers that case already. > > > + mm = task->mm; > > + mmget(mm); > > All you need is to make sure mm will not get released under your feet > once task_lock is released so mmgrab is the right thing to do here. The > address space can be torn down in parallel and that is OK and desirable. > > I think you really want something like this: > > if (flags) > return -EINVAL; > > pid = pidfd_get_pid(fd, &f_flags); > if (IS_ERR(pid)) > return PTR_ERR(pid); > task = get_pid_task(pid, PIDTYPE_PID); > if (!task) { > ret = -ESRCH; > goto put_pid; > } > > /* > * Make sure to chose a thread which still has a reference to mm > * during the group exit > */ > p = find_lock_task_mm(task); > if (!p) { > ret = -ESRCH; > goto put_task; > } > > mm = task->mm; > mmgrab(mm); > reap = true; > /* If the work has been done already, just exit with success */ > if (test_bit(MMF_OOM_SKIP, &mm->flags)) { > reap = false; > } else if (!task_will_free_mem(p)) { > reap = false; > ret = -EINVAL; > } > task_unlock(p); > > if (!reap) > goto dropmm;; > > /* Do the work*/ > > > dropmm: > mmdrop(mm); > put_task: > put_task(task); > put_pid: > put_pid(pid); > > return ret; > This is indeed simpler to follow. I'll adopt your version. Thanks! > -- > Michal Hocko > SUSE Labs