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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: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 1D2D21C0011 X-Rspam-User: X-Rspamd-Server: rspam11 X-Stat-Signature: uyseeym1r9yrh4j74jkxdzhqu7o3xeu9 X-HE-Tag: 1705988194-806690 X-HE-Meta: U2FsdGVkX19MaveyfjzhKbOMP1D20z8KTUMzO1xv2xu6X+hyASE91YfijJ/z98TZhHPHEgnjcEF1RuuWTFaldWJmmGyMbuok0AYQbkhXw6jqvFA7//Imxe3SNUsBr+wrGjtHvDH79PkeaJeQbmsEZ4Fgh3MP7diRTpGxkZ4QN6Nfy9eblStqJ0t3/W6UlRCrM9+3g0/I++K4isYWJ8DayPKgtprC9P61t4QcxIcVG3PrqRuloQEOl1I7SsSdsqEdvNA3/XE4iuypi2G/5EV2ugmGzu105kleIrM6yTEUjV0lGOP6ykfYtj66+DhcMv/ycm5a6eUVkfnStpUatLl1qXf57IEEU5dkxmCnTqplddUDpdS1oXPa1k23nLSLVj1YRXjjYrn7o6S8O6yspxAJ3WucCgT3CY+iZ3rF9Kt6mDjWSFY8Uy/maNMRAGX+iMCqxOd/+eB/8t3suTheW00CXRapMDD2QodYLRGHrIPa574F6t9RIQ1oilzOm1JroI92eCm0Agc8xWJFdREgrVz7vieZltnRbwv2FFVKTnCmGszaWKmNBOI68/9DWVwyZc4yIGIkkZ6W8zpZuoWlEjUM8SHr8bJeyqx5RL1+xUFfEHXGu9qOlRUs8nJEYZdOCVRKUWczZ0KLC1ztvqObCR0PL8JG53ptEUB5gr370LbQmiuo3xmqzxxypRorO5Hazq0jB+MnXmcmGkvPIZuO8NB9C9aU8cp+ne+Z5JK4OWtx/imCYFNtOsFBfOM4+O+xvSGsJMODo2HLWhmOir7uZNaHQ+Dt+bdd0Gtt38Vg3i2VyYI65rGbEOv99b+1b1KvozJGfQGHYG1/KH4jABFygWijIqVEswvOf3dIq+73PvXamzWRTO/AR+/XV1ItdV1vPQofkmDA8IOABPR3rwKN1Xc0c1yEXW4/hvjSyjG4iVweT4XP5sRy84G5erFMvL0ZHDMG/2gSG5/kjB1+MYEvQAK T+Z1sEzr 3s0gZdI38f6d5+jEddQg2N6YjP2JAzv9zbNwEYeaXLR3RXZhr6/SpShGtFk1YwgEoXNgL/iYVENt9CqH8pRBcxVu5R4yxvjXnkBKgOIdDGC7bW3g8ce5rq6pg2TTndcqVUbc+0jrxB7enPA3uta78VxYpg3eElivfr4y0vg4ZZDwaoa6eHF6pwTuny4Ojn5qMEIxh6I5RaSfy4UDN+nYlz4d7ZPRNLtmqUYWYekNVvoDSHSY19D5SPr0lSV98yGkGQM13tB9digaF0cwmeDxkXjzoa05dtBcM/mRG 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: List-Subscribe: List-Unsubscribe: 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