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Fri, 16 Oct 2020 10:45:18 +0000 (UTC) From: mwilck@suse.com To: Christophe Varoqui , Benjamin Marzinski Date: Fri, 16 Oct 2020 12:45:01 +0200 Message-Id: <20201016104501.8700-30-mwilck@suse.com> In-Reply-To: <20201016104501.8700-1-mwilck@suse.com> References: <20201016104501.8700-1-mwilck@suse.com> MIME-Version: 1.0 X-Mimecast-Impersonation-Protect: Policy=CLT - Impersonation Protection Definition; Similar Internal Domain=false; Similar Monitored External Domain=false; Custom External Domain=false; Mimecast External Domain=false; Newly Observed Domain=false; Internal User Name=false; Custom Display Name List=false; Reply-to Address Mismatch=false; Targeted Threat Dictionary=false; Mimecast Threat Dictionary=false; Custom Threat Dictionary=false X-Scanned-By: MIMEDefang 2.78 on 10.11.54.4 X-MIME-Autoconverted: from quoted-printable to 8bit by lists01.pubmisc.prod.ext.phx2.redhat.com id 09GAjMNS020835 X-loop: dm-devel@redhat.com Cc: lixiaokeng@huawei.com, dm-devel@redhat.com, Martin Wilck Subject: [dm-devel] [PATCH v2 29/29] libmultipath: fix race between log_safe and log_thread_stop() X-BeenThere: dm-devel@redhat.com X-Mailman-Version: 2.1.12 Precedence: junk List-Id: device-mapper development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=dm-devel-bounces@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit From: Martin Wilck log_safe() could race with log_thread_stop(); simply checking the value of log_thr has never been safe. By converting the mutexes to static initializers, we avoid having to destroy them, and thus possibly accessing a destroyed mutex in log_safe(). Furthermore, taking both the logev_lock and the logq_lock makes sure the logarea isn't freed while we are writing to it. Signed-off-by: Martin Wilck --- libmultipath/log_pthread.c | 39 ++++++++++++++++++++++++-------------- 1 file changed, 25 insertions(+), 14 deletions(-) diff --git a/libmultipath/log_pthread.c b/libmultipath/log_pthread.c index 3c73941..91c9c19 100644 --- a/libmultipath/log_pthread.c +++ b/libmultipath/log_pthread.c @@ -17,31 +17,42 @@ static pthread_t log_thr; -static pthread_mutex_t logq_lock; -static pthread_mutex_t logev_lock; -static pthread_cond_t logev_cond; +/* logev_lock must not be taken with logq_lock held */ +static pthread_mutex_t logq_lock = PTHREAD_MUTEX_INITIALIZER; +static pthread_mutex_t logev_lock = PTHREAD_MUTEX_INITIALIZER; +static pthread_cond_t logev_cond = PTHREAD_COND_INITIALIZER; static int logq_running; static int log_messages_pending; void log_safe (int prio, const char * fmt, va_list ap) { + bool running; + if (prio > LOG_DEBUG) prio = LOG_DEBUG; - if (log_thr == (pthread_t)0) { - vsyslog(prio, fmt, ap); - return; - } + /* + * logev_lock protects logq_running. By holding it, we avoid a race + * with log_thread_stop() -> log_close(), which would free the logarea. + */ + pthread_mutex_lock(&logev_lock); + pthread_cleanup_push(cleanup_mutex, &logev_lock); + running = logq_running; - pthread_mutex_lock(&logq_lock); - log_enqueue(prio, fmt, ap); - pthread_mutex_unlock(&logq_lock); + if (running) { + pthread_mutex_lock(&logq_lock); + pthread_cleanup_push(cleanup_mutex, &logq_lock); + log_enqueue(prio, fmt, ap); + pthread_cleanup_pop(1); - pthread_mutex_lock(&logev_lock); - log_messages_pending = 1; - pthread_cond_signal(&logev_cond); - pthread_mutex_unlock(&logev_lock); + log_messages_pending = 1; + pthread_cond_signal(&logev_cond); + } + pthread_cleanup_pop(1); + + if (!running) + vsyslog(prio, fmt, ap); } static void flush_logqueue (void) -- 2.28.0 -- dm-devel mailing list dm-devel@redhat.com https://www.redhat.com/mailman/listinfo/dm-devel