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[2a00:1028:838d:271e:8e3b:4aff:fe4c:a100]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-490bc391aaasm64262115e9.1.2026.06.04.01.40.14 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 04 Jun 2026 01:40:15 -0700 (PDT) Message-ID: <2d797a44-bdd4-4b37-8bdd-2e2052c6dd38@suse.com> Date: Thu, 4 Jun 2026 10:40:14 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] module: stats: add lockdep annotation for dup_failed_modules list traversal To: Naveen Kumar Chaudhary Cc: mcgrof@kernel.org, da.gomez@kernel.org, samitolvanen@google.com, atomlin@atomlin.com, linux-modules@vger.kernel.org, linux-kernel@vger.kernel.org References: Content-Language: en-US From: Petr Pavlu In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 6/3/26 6:22 PM, Naveen Kumar Chaudhary wrote: > read_file_mod_stats() traverses dup_failed_modules with > list_for_each_entry_rcu() while holding module_mutex, but does not pass > the lockdep condition. This triggers a false-positive "RCU-list traversed > in non-reader section" warning with CONFIG_PROVE_RCU_LIST=y. > > The warning can be reproduced by: > 1. Racing two loads of the same module to populate dup_failed_modules: > insmod dummy.ko & > insmod dummy.ko & > 2. Reading the stats debugfs file: > cat /sys/kernel/debug/modules/stats > > ============================= > WARNING: suspicious RCU usage > 7.1.0-rc5-gae12a56ba16a #1 Not tainted > ----------------------------- > kernel/module/stats.c:385 RCU-list traversed in non-reader section!! > > other info that might help us debug this: > > rcu_scheduler_active = 2, debug_locks = 1 > 1 lock held by cat/128: > #0: ffff80008288f7a8 (module_mutex){+.+.}-{4:4}, at: read_file_mod_stats+0x46c/0x5ec > > stack backtrace: > CPU: 1 UID: 0 PID: 128 Comm: cat Kdump: loaded Not tainted 7.1.0-rc5-gae12a56ba16a #1 PREEMPT > Hardware name: linux,dummy-virt (DT) > Call trace: > show_stack+0x18/0x24 (C) > __dump_stack+0x28/0x38 > dump_stack_lvl+0x64/0x84 > dump_stack+0x18/0x24 > lockdep_rcu_suspicious+0x134/0x1d4 > read_file_mod_stats+0x554/0x5ec > full_proxy_read+0xe0/0x1ac > vfs_read+0xd8/0x2b0 > ksys_read+0x70/0xe4 > __arm64_sys_read+0x1c/0x28 > invoke_syscall+0x48/0xf8 > el0_svc_common+0x8c/0xd8 > do_el0_svc+0x1c/0x28 > el0_svc+0x58/0x1d8 > el0t_64_sync_handler+0x84/0x12c > el0t_64_sync+0x198/0x19c > > The traversal is protected by module_mutex, so pass > lockdep_is_held(&module_mutex) to inform the checker. > > Signed-off-by: Naveen Kumar Chaudhary > --- > kernel/module/stats.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/kernel/module/stats.c b/kernel/module/stats.c > index 3a9672f93a8e..a62961acd8e3 100644 > --- a/kernel/module/stats.c > +++ b/kernel/module/stats.c > @@ -382,7 +382,8 @@ static ssize_t read_file_mod_stats(struct file *file, char __user *user_buf, > mutex_lock(&module_mutex); > > > - list_for_each_entry_rcu(mod_fail, &dup_failed_modules, list) { > + list_for_each_entry_rcu(mod_fail, &dup_failed_modules, list, > + lockdep_is_held(&module_mutex)) { > if (WARN_ON_ONCE(++count_failed >= MAX_FAILED_MOD_PRINT)) > goto out_unlock; > len += scnprintf(buf + len, size - len, "%25s\t%15lu\t%25s\n", mod_fail->name, I mentioned in my reply to your previous patch fixing the use of synchronize_rcu() in the module dups code [1] that the overall RCU usage in this code appears to be incorrect. I also noticed that Sashiko reported the same issue. I think it is not very productive to try to fix these specific RCU-related problems and instead the code should be properly reworked. It most likely should not be using RCU at all and kmod_dup_req should instead be reference-counted. [1] https://lore.kernel.org/linux-modules/ajydyxgaea27rhcopp5eauji24znotu65d2b4uw344yvmwcc6f@7l5re6f2xcuk/ -- Thanks, Petr