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Mon, 30 Aug 2021 10:29:58 -0700 (PDT) Date: Mon, 30 Aug 2021 10:29:53 -0700 Message-Id: <20210830172953.207257-1-shakeelb@google.com> Mime-Version: 1.0 X-Mailer: git-send-email 2.33.0.259.gc128427fd7-goog Subject: [PATCH] memcg: make memcg->event_list_lock irqsafe From: Shakeel Butt To: Tejun Heo , Johannes Weiner , Michal Hocko Cc: Andrew Morton , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Shakeel Butt Content-Type: text/plain; charset="UTF-8" Authentication-Results: imf27.hostedemail.com; dkim=pass header.d=google.com header.s=20161025 header.b=IvtVU2ec; spf=pass (imf27.hostedemail.com: domain of 3lhUtYQgKCIU1qjtnnukpxxpun.lxvurw36-vvt4jlt.x0p@flex--shakeelb.bounces.google.com designates 209.85.216.73 as permitted sender) smtp.mailfrom=3lhUtYQgKCIU1qjtnnukpxxpun.lxvurw36-vvt4jlt.x0p@flex--shakeelb.bounces.google.com; dmarc=pass (policy=reject) header.from=google.com X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 9E0D170000A0 X-Stat-Signature: wms5mgz4t513hycjja4icqww5t9dzfcc X-HE-Tag: 1630344599-265167 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: The memcg->event_list_lock is usually taken in the normal context but when the userspace closes the corresponding eventfd, eventfd_release through memcg_event_wake takes memcg->event_list_lock with interrupts disabled. This is not an issue on its own but it creates a nested dependency from eventfd_ctx->wqh.lock to memcg->event_list_lock. Independently, for unrelated eventfd, eventfd_signal() can be called in the irq context, thus making eventfd_ctx->wqh.lock an irq lock. For example, FPGA DFL driver, VHOST VPDA driver and couple of VFIO drivers. This will force memcg->event_list_lock to be an irqsafe lock as well. One way to break the nested dependency between eventfd_ctx->wqh.lock and memcg->event_list_lock is to add an indirection. However the simplest solution would be to make memcg->event_list_lock irqsafe. This is cgroup v1 feature, is in maintenance and may get deprecated in near future. So, no need to add more code. BTW this has been discussed previously [1] but there weren't irq users of eventfd_signal() at the time. [1] https://www.spinics.net/lists/cgroups/msg06248.html Signed-off-by: Shakeel Butt --- mm/memcontrol.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 999e626f4111..a73689caee5d 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -4851,9 +4851,9 @@ static ssize_t memcg_write_event_control(struct kernfs_open_file *of, vfs_poll(efile.file, &event->pt); - spin_lock(&memcg->event_list_lock); + spin_lock_irq(&memcg->event_list_lock); list_add(&event->list, &memcg->event_list); - spin_unlock(&memcg->event_list_lock); + spin_unlock_irq(&memcg->event_list_lock); fdput(cfile); fdput(efile); @@ -5280,12 +5280,12 @@ static void mem_cgroup_css_offline(struct cgroup_subsys_state *css) * Notify userspace about cgroup removing only after rmdir of cgroup * directory to avoid race between userspace and kernelspace. */ - spin_lock(&memcg->event_list_lock); + spin_lock_irq(&memcg->event_list_lock); list_for_each_entry_safe(event, tmp, &memcg->event_list, list) { list_del_init(&event->list); schedule_work(&event->remove); } - spin_unlock(&memcg->event_list_lock); + spin_unlock_irq(&memcg->event_list_lock); page_counter_set_min(&memcg->memory, 0); page_counter_set_low(&memcg->memory, 0); -- 2.33.0.259.gc128427fd7-goog