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Thu, 18 Jun 2020 07:34:53 +0000 (UTC) Subject: Re: [PATCH v8 13/21] main: keep rcu_atfork callback enabled for qtest To: "Bulekov, Alexander" , "qemu-devel@nongnu.org" References: <20200129053357.27454-1-alxndr@bu.edu> <20200129053357.27454-14-alxndr@bu.edu> From: Thomas Huth Openpgp: preference=signencrypt Message-ID: <199e36b2-a509-00ed-94a7-0624753eb53f@redhat.com> Date: Thu, 18 Jun 2020 09:34:51 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.9.0 MIME-Version: 1.0 In-Reply-To: <20200129053357.27454-14-alxndr@bu.edu> Content-Language: en-US X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=205.139.110.120; envelope-from=thuth@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/06/18 01:21:16 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=-0.01, RCVD_IN_MSPIKE_WL=-0.01, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=_AUTOLEARN X-Spam_action: no action 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: "pbonzini@redhat.com" , "bsd@redhat.com" , "stefanha@redhat.com" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 29/01/2020 06.34, Bulekov, Alexander wrote: > The qtest-based fuzzer makes use of forking to reset-state between > tests. Keep the callback enabled, so the call_rcu thread gets created > within the child process. > > Signed-off-by: Alexander Bulekov > --- > vl.c | 9 ++++++++- > 1 file changed, 8 insertions(+), 1 deletion(-) > > diff --git a/vl.c b/vl.c > index bb77935f04..cf8e2d3ebb 100644 > --- a/vl.c > +++ b/vl.c > @@ -3794,7 +3794,14 @@ void qemu_init(int argc, char **argv, char **envp) > set_memory_options(&ram_slots, &maxram_size, machine_class); > > os_daemonize(); > - rcu_disable_atfork(); > + > + /* > + * If QTest is enabled, keep the rcu_atfork enabled, since system processes > + * may be forked testing purposes (e.g. fork-server based fuzzing) > + */ > + if (!qtest_enabled()) { > + rcu_disable_atfork(); > + } > > if (pid_file && !qemu_write_pidfile(pid_file, &err)) { > error_reportf_err(err, "cannot create PID file: "); Hi Alexander, I think this patch might maybe not work as expected: The qtest_enabled() has been added before configure_accelerators() is called in main(). So qtest_enabled() should always return "false" and thus rcu_disabled_fork() is still called in any case... could you please double-check whether it works for you and I just made a mistake, or whether this is a bug indeed? Thanks, Thomas