From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-19.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C7FA4C11F76 for ; Mon, 12 Jul 2021 08:34:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BD4BA6113E for ; Mon, 12 Jul 2021 08:34:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1377762AbhGLIgY (ORCPT ); Mon, 12 Jul 2021 04:36:24 -0400 Received: from mail.kernel.org ([198.145.29.99]:35482 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1350404AbhGLHu7 (ORCPT ); Mon, 12 Jul 2021 03:50:59 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id CE2CE61953; Mon, 12 Jul 2021 07:45:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1626075918; bh=LEaUvOGmtjnNWHHqHt2TzPzUVP0K1SqxJk02a9w+omI=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Yb1uk6vnq5uIhWaKm4foZzl6NU1NMINjgoPbFL+KOsfEVb4pEd6UdUfpcfsknnuP3 HAaJ/2NR/LIOkLQBNO2WqLrWTrexXY+xehzokWmiyw5cz2w0GvXtLg8kTUM2G4Zq7x 8MmAufmidaXIw3S2xljnwQjWtSAn+nDgRQIazflk= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Nicolas Saenz Julienne , Axel Rasmussen , Vlastimil Babka , Steven Rostedt , Andrew Morton , Linus Torvalds , Sasha Levin Subject: [PATCH 5.13 383/800] mm: mmap_lock: use local locks instead of disabling preemption Date: Mon, 12 Jul 2021 08:06:46 +0200 Message-Id: <20210712061007.921054564@linuxfoundation.org> X-Mailer: git-send-email 2.32.0 In-Reply-To: <20210712060912.995381202@linuxfoundation.org> References: <20210712060912.995381202@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Nicolas Saenz Julienne [ Upstream commit 832b50725373e8c46781b7d4db104ec9cf564a6b ] mmap_lock will explicitly disable/enable preemption upon manipulating its local CPU variables. This is to be expected, but in this case, it doesn't play well with PREEMPT_RT. The preemption disabled code section also takes a spin-lock. Spin-locks in RT systems will try to schedule, which is exactly what we're trying to avoid. To mitigate this, convert the explicit preemption handling to local_locks. Which are RT aware, and will disable migration instead of preemption when PREEMPT_RT=y. The faulty call trace looks like the following: __mmap_lock_do_trace_*() preempt_disable() get_mm_memcg_path() cgroup_path() kernfs_path_from_node() spin_lock_irqsave() /* Scheduling while atomic! */ Link: https://lkml.kernel.org/r/20210604163506.2103900-1-nsaenzju@redhat.com Fixes: 2b5067a8143e3 ("mm: mmap_lock: add tracepoints around lock acquisition ") Signed-off-by: Nicolas Saenz Julienne Tested-by: Axel Rasmussen Reviewed-by: Axel Rasmussen Cc: Vlastimil Babka Cc: Steven Rostedt Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Sasha Levin --- mm/mmap_lock.c | 33 ++++++++++++++++++++++----------- 1 file changed, 22 insertions(+), 11 deletions(-) diff --git a/mm/mmap_lock.c b/mm/mmap_lock.c index dcdde4f722a4..2ae3f33b85b1 100644 --- a/mm/mmap_lock.c +++ b/mm/mmap_lock.c @@ -11,6 +11,7 @@ #include #include #include +#include EXPORT_TRACEPOINT_SYMBOL(mmap_lock_start_locking); EXPORT_TRACEPOINT_SYMBOL(mmap_lock_acquire_returned); @@ -39,21 +40,30 @@ static int reg_refcount; /* Protected by reg_lock. */ */ #define CONTEXT_COUNT 4 -static DEFINE_PER_CPU(char __rcu *, memcg_path_buf); +struct memcg_path { + local_lock_t lock; + char __rcu *buf; + local_t buf_idx; +}; +static DEFINE_PER_CPU(struct memcg_path, memcg_paths) = { + .lock = INIT_LOCAL_LOCK(lock), + .buf_idx = LOCAL_INIT(0), +}; + static char **tmp_bufs; -static DEFINE_PER_CPU(int, memcg_path_buf_idx); /* Called with reg_lock held. */ static void free_memcg_path_bufs(void) { + struct memcg_path *memcg_path; int cpu; char **old = tmp_bufs; for_each_possible_cpu(cpu) { - *(old++) = rcu_dereference_protected( - per_cpu(memcg_path_buf, cpu), + memcg_path = per_cpu_ptr(&memcg_paths, cpu); + *(old++) = rcu_dereference_protected(memcg_path->buf, lockdep_is_held(®_lock)); - rcu_assign_pointer(per_cpu(memcg_path_buf, cpu), NULL); + rcu_assign_pointer(memcg_path->buf, NULL); } /* Wait for inflight memcg_path_buf users to finish. */ @@ -88,7 +98,7 @@ int trace_mmap_lock_reg(void) new = kmalloc(MEMCG_PATH_BUF_SIZE * CONTEXT_COUNT, GFP_KERNEL); if (new == NULL) goto out_fail_free; - rcu_assign_pointer(per_cpu(memcg_path_buf, cpu), new); + rcu_assign_pointer(per_cpu_ptr(&memcg_paths, cpu)->buf, new); /* Don't need to wait for inflights, they'd have gotten NULL. */ } @@ -122,23 +132,24 @@ out: static inline char *get_memcg_path_buf(void) { + struct memcg_path *memcg_path = this_cpu_ptr(&memcg_paths); char *buf; int idx; rcu_read_lock(); - buf = rcu_dereference(*this_cpu_ptr(&memcg_path_buf)); + buf = rcu_dereference(memcg_path->buf); if (buf == NULL) { rcu_read_unlock(); return NULL; } - idx = this_cpu_add_return(memcg_path_buf_idx, MEMCG_PATH_BUF_SIZE) - + idx = local_add_return(MEMCG_PATH_BUF_SIZE, &memcg_path->buf_idx) - MEMCG_PATH_BUF_SIZE; return &buf[idx]; } static inline void put_memcg_path_buf(void) { - this_cpu_sub(memcg_path_buf_idx, MEMCG_PATH_BUF_SIZE); + local_sub(MEMCG_PATH_BUF_SIZE, &this_cpu_ptr(&memcg_paths)->buf_idx); rcu_read_unlock(); } @@ -179,14 +190,14 @@ out: #define TRACE_MMAP_LOCK_EVENT(type, mm, ...) \ do { \ const char *memcg_path; \ - preempt_disable(); \ + local_lock(&memcg_paths.lock); \ memcg_path = get_mm_memcg_path(mm); \ trace_mmap_lock_##type(mm, \ memcg_path != NULL ? memcg_path : "", \ ##__VA_ARGS__); \ if (likely(memcg_path != NULL)) \ put_memcg_path_buf(); \ - preempt_enable(); \ + local_unlock(&memcg_paths.lock); \ } while (0) #else /* !CONFIG_MEMCG */ -- 2.30.2