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=-6.5 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 E3B2AC17441 for ; Tue, 12 Nov 2019 17:37:54 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id A1129214E0 for ; Tue, 12 Nov 2019 17:37:54 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=linaro.org header.i=@linaro.org header.b="v7CvWN1X" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A1129214E0 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linaro.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:38160 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iUa6z-0000Um-MA for qemu-devel@archiver.kernel.org; Tue, 12 Nov 2019 12:37:53 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:34021) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iUa5r-0008Sc-F7 for qemu-devel@nongnu.org; Tue, 12 Nov 2019 12:36:45 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1iUa5p-0004n1-EB for qemu-devel@nongnu.org; Tue, 12 Nov 2019 12:36:43 -0500 Received: from mail-wm1-x342.google.com ([2a00:1450:4864:20::342]:33046) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1iUa5p-0004mZ-3h for qemu-devel@nongnu.org; Tue, 12 Nov 2019 12:36:41 -0500 Received: by mail-wm1-x342.google.com with SMTP id a17so2886738wmb.0 for ; Tue, 12 Nov 2019 09:36:40 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=references:user-agent:from:to:cc:subject:in-reply-to:date :message-id:mime-version:content-transfer-encoding; bh=HNnxjFmrqoWz6Job3vp1ljHdw2Aiy+AK2bbUwC+SXy4=; b=v7CvWN1XwcQ3OukyOdzVk4BWKdYokL24fVB4WeGVkcX7VrydqITvS+/TUSNsVL0k0j VHMm5Nqm47qMJ/q5n4VrzttgHNrgW2f+n7l51JV6BgZMOnq47HNBYGq+feuXlGHlXjlE 17LpmxqP2gbHESihkqNzpeYzoYdCrpDWFPZ/A997AA1XK0vbwwExs7NhChySSnWhZvSw 3lv0PmWFgpxvbvT0q1JF8FNcnFfCnXntFCtHMnlU1ThSXT5cPHurjgOvmoNKYkNC6A3y MCMBlDX81uxOW0mSsUv0ErEEAhMXzTwC7XpCTJ7VIXMuJxg0YhwdUEnLLYXRSFRkm19U LFDQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:references:user-agent:from:to:cc:subject :in-reply-to:date:message-id:mime-version:content-transfer-encoding; bh=HNnxjFmrqoWz6Job3vp1ljHdw2Aiy+AK2bbUwC+SXy4=; b=OOAQQS85J8pZjGbdgiHiXb72Z3hvmmq1tItROlMfQVMdAUUjNJs24grvSDuKa7aOB0 MZ/sntlIMoHqOKco5KM5ewNUmGCsGoTIbukclthf59E7P4HTkxZFd42Ko1zXohW9Pebh wqBVPZz+fapGJX6LyhGYRQy58dDLvyCjn9jruHBkbi1KyiTJIWGh5kROL2LPP5IvvJCe xVhkOLZEU2sQf/PUc8qRUhi2Opx79jeEVoZbR0nJqaftu0zpYfl7sLEtCQNmKdF5en0e ZlnjW0caye3xoLgNY5sfdBZiaQV2veKBltc+YR15K0QQYbpv2DDMxAcGKgUPAHIkoj4y Tq/A== X-Gm-Message-State: APjAAAWyiIVUaXfoiTfuM4k6BofeXIfFih/+QmDzoybCy7nyqhdXrvA1 /v/UAUC4VcIGhXwaW+YitVbnVg== X-Google-Smtp-Source: APXvYqzRGdZ+8JCHNbEIp4CyDGFAzKXpqWfQ3/MJ1xZTquCREaHQ+2gALyusSh3yrFGYoxke2EE7Sg== X-Received: by 2002:a7b:ce84:: with SMTP id q4mr4729339wmj.36.1573580199242; Tue, 12 Nov 2019 09:36:39 -0800 (PST) Received: from zen.linaroharston ([51.148.130.216]) by smtp.gmail.com with ESMTPSA id h140sm4553555wme.22.2019.11.12.09.36.37 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 12 Nov 2019 09:36:37 -0800 (PST) Received: from zen (localhost [127.0.0.1]) by zen.linaroharston (Postfix) with ESMTP id 2A6F31FF87; Tue, 12 Nov 2019 17:36:37 +0000 (GMT) References: <20191112150105.2498-1-robert.foley@linaro.org> <20191112150105.2498-4-robert.foley@linaro.org> User-agent: mu4e 1.3.5; emacs 27.0.50 From: Alex =?utf-8?Q?Benn=C3=A9e?= To: Robert Foley Subject: Re: [PATCH v1 3/5] Add use of RCU for qemu_logfile. In-reply-to: <20191112150105.2498-4-robert.foley@linaro.org> Date: Tue, 12 Nov 2019 17:36:37 +0000 Message-ID: <87lfsl809m.fsf@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: Genre and OS details not recognized. X-Received-From: 2a00:1450:4864:20::342 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: peter.puhov@linaro.org, qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Robert Foley writes: > This now allows changing the logfile while logging is active, > and also solves the issue of a seg fault while changing the logfile. > > Any read access to the qemu_logfile handle will use > the rcu_read_lock()/unlock() around the use of the handle. > To fetch the handle we will use atomic_rcu_read(). > We also in many cases do a check for validity of the > logfile handle before using it to deal with the case where the > file is closed and set to NULL. > > The cases where we write to the qemu_logfile will use atomic_rcu_set(). > Writers will also use call_rcu() with a newly added qemu_logfile_free > function for freeing/closing when readers have finished. > > Signed-off-by: Robert Foley > --- > v1 > - Changes for review comments. > - Minor changes to definition of QemuLogFile. > - Changed qemu_log_separate() to fix unbalanced and > remove qemu_log_enabled() check. > - changed qemu_log_lock() to include else. > - make qemu_logfile_free static. > - use g_assert(logfile) in qemu_logfile_free. > - Relocated unlock out of if/else in qemu_log_close(), and > in qemu_set_log(). > --- > include/qemu/log.h | 42 ++++++++++++++++++++++---- > util/log.c | 73 +++++++++++++++++++++++++++++++++------------- > include/exec/log.h | 33 ++++++++++++++++++--- > tcg/tcg.c | 12 ++++++-- > 4 files changed, 128 insertions(+), 32 deletions(-) > > diff --git a/include/qemu/log.h b/include/qemu/log.h > index a7c5b01571..528e1f9dd7 100644 > --- a/include/qemu/log.h > +++ b/include/qemu/log.h > @@ -3,9 +3,16 @@ > > /* A small part of this API is split into its own header */ > #include "qemu/log-for-trace.h" > +#include "qemu/rcu.h" > + > +typedef struct QemuLogFile { > + struct rcu_head rcu; > + FILE *fd; > +} QemuLogFile; > > /* Private global variable, don't use */ > -extern FILE *qemu_logfile; > +extern QemuLogFile *qemu_logfile; > + > > /* > * The new API: > @@ -25,7 +32,16 @@ static inline bool qemu_log_enabled(void) > */ > static inline bool qemu_log_separate(void) > { > - return qemu_logfile !=3D NULL && qemu_logfile !=3D stderr; > + QemuLogFile *logfile; > + bool res =3D false; > + > + rcu_read_lock(); > + logfile =3D atomic_rcu_read(&qemu_logfile); > + if (logfile && logfile->fd !=3D stderr) { > + res =3D true; > + } > + rcu_read_unlock(); > + return res; > } > > #define CPU_LOG_TB_OUT_ASM (1 << 0) > @@ -55,14 +71,23 @@ static inline bool qemu_log_separate(void) > > static inline FILE *qemu_log_lock(void) > { > - qemu_flockfile(qemu_logfile); > - return logfile->fd; > + QemuLogFile *logfile; > + rcu_read_lock(); > + logfile =3D atomic_rcu_read(&qemu_logfile); > + if (logfile) { > + qemu_flockfile(logfile->fd); > + return logfile->fd; > + } else { > + rcu_read_unlock(); > + return NULL; > + } > } > > static inline void qemu_log_unlock(FILE *fd) > { > if (fd) { > qemu_funlockfile(fd); > + rcu_read_unlock(); > } > } > > @@ -73,9 +98,14 @@ static inline void qemu_log_unlock(FILE *fd) > static inline void GCC_FMT_ATTR(1, 0) > qemu_log_vprintf(const char *fmt, va_list va) > { > - if (qemu_logfile) { > - vfprintf(qemu_logfile, fmt, va); > + QemuLogFile *logfile; > + > + rcu_read_lock(); > + logfile =3D atomic_rcu_read(&qemu_logfile); > + if (logfile) { > + vfprintf(logfile->fd, fmt, va); > } > + rcu_read_unlock(); > } > > /* log only if a bit is set on the current loglevel mask: > diff --git a/util/log.c b/util/log.c > index c25643dc99..802b8de42e 100644 > --- a/util/log.c > +++ b/util/log.c > @@ -28,7 +28,7 @@ > > static char *logfilename; > static QemuMutex qemu_logfile_mutex; > -FILE *qemu_logfile; > +QemuLogFile *qemu_logfile; > int qemu_loglevel; > static int log_append =3D 0; > static GArray *debug_regions; > @@ -37,10 +37,14 @@ static GArray *debug_regions; > int qemu_log(const char *fmt, ...) > { > int ret =3D 0; > - if (qemu_logfile) { > + QemuLogFile *logfile; > + > + rcu_read_lock(); > + logfile =3D atomic_rcu_read(&qemu_logfile); > + if (logfile) { > va_list ap; > va_start(ap, fmt); > - ret =3D vfprintf(qemu_logfile, fmt, ap); > + ret =3D vfprintf(logfile->fd, fmt, ap); > va_end(ap); > > /* Don't pass back error results. */ > @@ -48,6 +52,7 @@ int qemu_log(const char *fmt, ...) > ret =3D 0; > } > } > + rcu_read_unlock(); > return ret; > } > > @@ -56,11 +61,23 @@ static void __attribute__((__constructor__)) qemu_log= file_init(void) > qemu_mutex_init(&qemu_logfile_mutex); > } > > +static void qemu_logfile_free(QemuLogFile *logfile) > +{ > + g_assert(logfile); > + > + if (logfile->fd !=3D stderr) { > + fclose(logfile->fd); > + } > + g_free(logfile); > +} > + > static bool log_uses_own_buffers; > > /* enable or disable low levels log */ > void qemu_set_log(int log_flags) > { > + QemuLogFile *logfile; > + > qemu_loglevel =3D log_flags; > #ifdef CONFIG_TRACE_LOG > qemu_loglevel |=3D LOG_TRACE; > @@ -70,44 +87,50 @@ void qemu_set_log(int log_flags) > qemu_mutex_lock(&qemu_logfile_mutex); > if (!qemu_logfile && > (is_daemonized() ? logfilename !=3D NULL : qemu_loglevel)) { > + logfile =3D g_new0(QemuLogFile, 1); > if (logfilename) { > - qemu_logfile =3D fopen(logfilename, log_append ? "a" : "w"); > - if (!qemu_logfile) { > + logfile->fd =3D fopen(logfilename, log_append ? "a" : "w"); > + if (!logfile->fd) { > + g_free(logfile); > perror(logfilename); > _exit(1); > } > /* In case we are a daemon redirect stderr to logfile */ > if (is_daemonized()) { > - dup2(fileno(qemu_logfile), STDERR_FILENO); > - fclose(qemu_logfile); > + dup2(fileno(logfile->fd), STDERR_FILENO); > + fclose(logfile->fd); > /* This will skip closing logfile in qemu_log_close() */ > - qemu_logfile =3D stderr; > + logfile->fd =3D stderr; > } > } else { > /* Default to stderr if no log file specified */ > assert(!is_daemonized()); > - qemu_logfile =3D stderr; > + logfile->fd =3D stderr; > } > /* must avoid mmap() usage of glibc by setting a buffer "by hand= " */ > if (log_uses_own_buffers) { > static char logfile_buf[4096]; > > - setvbuf(qemu_logfile, logfile_buf, _IOLBF, sizeof(logfile_bu= f)); > + setvbuf(logfile->fd, logfile_buf, _IOLBF, sizeof(logfile_buf= )); > } else { > #if defined(_WIN32) > /* Win32 doesn't support line-buffering, so use unbuffered o= utput. */ > - setvbuf(qemu_logfile, NULL, _IONBF, 0); > + setvbuf(logfile->fd, NULL, _IONBF, 0); > #else > - setvbuf(qemu_logfile, NULL, _IOLBF, 0); > + setvbuf(logfile->fd, NULL, _IOLBF, 0); > #endif > log_append =3D 1; > } > + atomic_rcu_set(&qemu_logfile, logfile); > } > - qemu_mutex_unlock(&qemu_logfile_mutex); > + logfile =3D qemu_logfile; Isn't this read outside of the protection of both rcu_read_lock() and the mutex? Could that race? > + > if (qemu_logfile && > (is_daemonized() ? logfilename =3D=3D NULL : !qemu_loglevel)) { > - qemu_log_close(); > + atomic_rcu_set(&qemu_logfile, NULL); > + call_rcu(logfile, qemu_logfile_free, rcu); I wonder if we can re-arrange the logic here so it's lets confusing? For example the NULL qemu_loglevel can be detected at the start and we should be able just to squash the current log and reset and go. I'm not sure about the damonize/stdout check. > } > + qemu_mutex_unlock(&qemu_logfile_mutex); > } > > void qemu_log_needs_buffers(void) > @@ -123,6 +146,7 @@ void qemu_log_needs_buffers(void) > void qemu_set_log_filename(const char *filename, Error **errp) > { > char *pidstr; > + > g_free(logfilename); nit: stray newline > > pidstr =3D strstr(filename, "%"); > @@ -235,19 +259,28 @@ out: > /* fflush() the log file */ > void qemu_log_flush(void) > { > - fflush(qemu_logfile); > + QemuLogFile *logfile; > + > + rcu_read_lock(); > + logfile =3D atomic_rcu_read(&qemu_logfile); > + if (logfile) { > + fflush(logfile->fd); > + } > + rcu_read_unlock(); > } > > /* Close the log file */ > void qemu_log_close(void) > { > + QemuLogFile *logfile; > + > g_assert(qemu_logfile_mutex.initialized); > qemu_mutex_lock(&qemu_logfile_mutex); > - if (qemu_logfile) { > - if (qemu_logfile !=3D stderr) { > - fclose(qemu_logfile); > - } > - qemu_logfile =3D NULL; > + logfile =3D qemu_logfile; > + > + if (logfile) { > + atomic_rcu_set(&qemu_logfile, NULL); > + call_rcu(logfile, qemu_logfile_free, rcu); > } > qemu_mutex_unlock(&qemu_logfile_mutex); > } > diff --git a/include/exec/log.h b/include/exec/log.h > index e2cfd436e6..9bd1e4aa20 100644 > --- a/include/exec/log.h > +++ b/include/exec/log.h > @@ -15,8 +15,15 @@ > */ > static inline void log_cpu_state(CPUState *cpu, int flags) > { > + QemuLogFile *logfile; > + > if (qemu_log_enabled()) { > - cpu_dump_state(cpu, qemu_logfile, flags); > + rcu_read_lock(); > + logfile =3D atomic_rcu_read(&qemu_logfile); > + if (logfile) { > + cpu_dump_state(cpu, logfile->fd, flags); > + } > + rcu_read_unlock(); > } > } > > @@ -40,19 +47,37 @@ static inline void log_cpu_state_mask(int mask, CPUSt= ate *cpu, int flags) > static inline void log_target_disas(CPUState *cpu, target_ulong start, > target_ulong len) > { > - target_disas(qemu_logfile, cpu, start, len); > + QemuLogFile *logfile; > + rcu_read_lock(); > + logfile =3D atomic_rcu_read(&qemu_logfile); > + if (logfile) { > + target_disas(logfile->fd, cpu, start, len); > + } > + rcu_read_unlock(); > } > > static inline void log_disas(void *code, unsigned long size) > { > - disas(qemu_logfile, code, size); > + QemuLogFile *logfile; > + rcu_read_lock(); > + logfile =3D atomic_rcu_read(&qemu_logfile); > + if (logfile) { > + disas(logfile->fd, code, size); > + } > + rcu_read_unlock(); > } > > #if defined(CONFIG_USER_ONLY) > /* page_dump() output to the log file: */ > static inline void log_page_dump(void) > { > - page_dump(qemu_logfile); > + QemuLogFile *logfile; > + rcu_read_lock(); > + logfile =3D atomic_rcu_read(&qemu_logfile); > + if (logfile) { > + page_dump(logfile->fd); > + } > + rcu_read_unlock(); > } > #endif > #endif > diff --git a/tcg/tcg.c b/tcg/tcg.c > index 0511266d85..4f616ba38b 100644 > --- a/tcg/tcg.c > +++ b/tcg/tcg.c > @@ -2114,9 +2114,17 @@ static void tcg_dump_ops(TCGContext *s, bool have_= prefs) > } > > if (have_prefs || op->life) { > - for (; col < 40; ++col) { > - putc(' ', qemu_logfile); > + > + QemuLogFile *logfile; > + > + rcu_read_lock(); > + logfile =3D atomic_rcu_read(&qemu_logfile); > + if (logfile) { > + for (; col < 40; ++col) { > + putc(' ', logfile->fd); > + } > } > + rcu_read_unlock(); > } > > if (op->life) { -- Alex Benn=C3=A9e