From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 3239323BC; Tue, 23 Jan 2024 05:36:33 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1705988194; cv=none; b=QSCzVAUX++kgOgoyhAwApebySuz3Xrk5yFL6CY0+kbYmJ9Zt6s+ZrkhR3uJdf6dpgsFqx5vESlYgEzMG240fog3q6ZvVJ8C1GxlPQz0mb9X1rw9T6canaSQtRHA4/qTPh9gJzPT9nB0zkrylZg8vVSKOzuMTRDDZ4mrcAFObMLE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1705988194; c=relaxed/simple; bh=XcUyx0Kg5/x6d2IpLX/qANXj9xdB4k83aNsft2ltqyo=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version:Content-Type; b=LPHMyGf/+qQAUzWQOO1pXFyPJiGV/YXzxDsEGh+fkhsEbo03Zonx7bCdAc9QH6SV2NDFO9JBmkBll9XD70nTukDSLntVGEeOxPszu+zevx1evl/TZmeedWudmIb6VU2s+N2Jg5dJDj8Z4raTzEaVzIhzwK1gFhDyWd9P9lFS72k= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=rxuJVbct; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="rxuJVbct" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 342CEC433C7; Tue, 23 Jan 2024 05:36:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1705988193; bh=XcUyx0Kg5/x6d2IpLX/qANXj9xdB4k83aNsft2ltqyo=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=rxuJVbctGlVRuiog03AjfM1ofgpReV8yuZ06WUjRbYUOC/oCSz8MXnhmA/zpfb52u 7N0hYad1xKNfHz5mX8mctlhMVgNDdICvXb5HDFWfZXdq9osHoHb7DmFLncMZ5sn5Lx szxArnmT1njinY0L1HohpN1axVehymgshEHtcj8tA1hgXmGSlb8MEXHabJFAczN9q4 mU4jPxrKw2775+vyPE+Fg2EtnyNa8HjDCVbxcPJdC9PAOJNSoQvb7B6fWOA/slwl23 yXS6B8pOECKegN8x1T8kzua8LH8sjlEjiXtoulTKIASXYExb5Ekddw+9O+RxTDWhcL LKvYZPRaRvlrw== From: SeongJae Park To: Suren Baghdasaryan Cc: akpm@linux-foundation.org, viro@zeniv.linux.org.uk, brauner@kernel.org, jack@suse.cz, dchinner@redhat.com, casey@schaufler-ca.com, ben.wolsieffer@hefring.com, paulmck@kernel.org, david@redhat.com, avagin@google.com, usama.anjum@collabora.com, peterx@redhat.com, hughd@google.com, ryan.roberts@arm.com, wangkefeng.wang@huawei.com, Liam.Howlett@Oracle.com, yuzhao@google.com, axelrasmussen@google.com, lstoakes@gmail.com, talumbau@google.com, willy@infradead.org, vbabka@suse.cz, mgorman@techsingularity.net, jhubbard@nvidia.com, vishal.moola@gmail.com, mathieu.desnoyers@efficios.com, dhowells@redhat.com, jgg@ziepe.ca, sidhartha.kumar@oracle.com, andriy.shevchenko@linux.intel.com, yangxingui@huawei.com, keescook@chromium.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, kernel-team@android.com Subject: Re: [PATCH 3/3] mm/maps: read proc/pid/maps under RCU Date: Mon, 22 Jan 2024 21:36:29 -0800 Message-Id: <20240123053629.365673-1-sj@kernel.org> X-Mailer: git-send-email 2.39.2 In-Reply-To: <20240122071324.2099712-3-surenb@google.com> References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Hi Suren, On Sun, 21 Jan 2024 23:13:24 -0800 Suren Baghdasaryan wrote: > With maple_tree supporting vma tree traversal under RCU and per-vma locks > making vma access RCU-safe, /proc/pid/maps can be read under RCU and > without the need to read-lock mmap_lock. However vma content can change > from under us, therefore we make a copy of the vma and we pin pointer > fields used when generating the output (currently only vm_file and > anon_name). Afterwards we check for concurrent address space > modifications, wait for them to end and retry. That last check is needed > to avoid possibility of missing a vma during concurrent maple_tree > node replacement, which might report a NULL when a vma is replaced > with another one. While we take the mmap_lock for reading during such > contention, we do that momentarily only to record new mm_wr_seq counter. > This change is designed to reduce mmap_lock contention and prevent a > process reading /proc/pid/maps files (often a low priority task, such as > monitoring/data collection services) from blocking address space updates. > > Note that this change has a userspace visible disadvantage: it allows for > sub-page data tearing as opposed to the previous mechanism where data > tearing could happen only between pages of generated output data. > Since current userspace considers data tearing between pages to be > acceptable, we assume is will be able to handle sub-page data tearing > as well. > > Signed-off-by: Suren Baghdasaryan > --- > fs/proc/internal.h | 2 + > fs/proc/task_mmu.c | 114 ++++++++++++++++++++++++++++++++++++++++++--- > 2 files changed, 109 insertions(+), 7 deletions(-) > > diff --git a/fs/proc/internal.h b/fs/proc/internal.h > index a71ac5379584..e0247225bb68 100644 > --- a/fs/proc/internal.h > +++ b/fs/proc/internal.h > @@ -290,6 +290,8 @@ struct proc_maps_private { > struct task_struct *task; > struct mm_struct *mm; > struct vma_iterator iter; > + unsigned long mm_wr_seq; > + struct vm_area_struct vma_copy; > #ifdef CONFIG_NUMA > struct mempolicy *task_mempolicy; > #endif > diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c > index 3f78ebbb795f..3886d04afc01 100644 > --- a/fs/proc/task_mmu.c > +++ b/fs/proc/task_mmu.c > @@ -126,11 +126,96 @@ static void release_task_mempolicy(struct proc_maps_private *priv) > } > #endif > > -static struct vm_area_struct *proc_get_vma(struct proc_maps_private *priv, > - loff_t *ppos) > +#ifdef CONFIG_PER_VMA_LOCK > + > +static const struct seq_operations proc_pid_maps_op; > +/* > + * Take VMA snapshot and pin vm_file and anon_name as they are used by > + * show_map_vma. > + */ > +static int get_vma_snapshow(struct proc_maps_private *priv, struct vm_area_struct *vma) > { > + struct vm_area_struct *copy = &priv->vma_copy; > + int ret = -EAGAIN; > + > + memcpy(copy, vma, sizeof(*vma)); > + if (copy->vm_file && !get_file_rcu(©->vm_file)) > + goto out; > + > + if (copy->anon_name && !anon_vma_name_get_rcu(copy)) > + goto put_file; >From today updated mm-unstable which containing this patch, I'm getting below build error when CONFIG_ANON_VMA_NAME is not set. Seems this patch needs to handle the case? .../linux/fs/proc/task_mmu.c: In function ‘get_vma_snapshow’: .../linux/fs/proc/task_mmu.c:145:19: error: ‘struct vm_area_struct’ has no member named ‘anon_name’; did you mean ‘anon_vma’? 145 | if (copy->anon_name && !anon_vma_name_get_rcu(copy)) | ^~~~~~~~~ | anon_vma .../linux/fs/proc/task_mmu.c:161:19: error: ‘struct vm_area_struct’ has no member named ‘anon_name’; did you mean ‘anon_vma’? 161 | if (copy->anon_name) | ^~~~~~~~~ | anon_vma .../linux/fs/proc/task_mmu.c:162:41: error: ‘struct vm_area_struct’ has no member named ‘anon_name’; did you mean ‘anon_vma’? 162 | anon_vma_name_put(copy->anon_name); | ^~~~~~~~~ | anon_vma .../linux/fs/proc/task_mmu.c: In function ‘put_vma_snapshot’: .../linux/fs/proc/task_mmu.c:174:18: error: ‘struct vm_area_struct’ has no member named ‘anon_name’; did you mean ‘anon_vma’? 174 | if (vma->anon_name) | ^~~~~~~~~ | anon_vma .../linux/fs/proc/task_mmu.c:175:40: error: ‘struct vm_area_struct’ has no member named ‘anon_name’; did you mean ‘anon_vma’? 175 | anon_vma_name_put(vma->anon_name); | ^~~~~~~~~ | anon_vma [...] Thanks, SJ