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Mon, 6 Mar 2023 15:29:28 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.39.193.92]) by smtp.corp.redhat.com (Postfix) with ESMTPS id EAE8FC1602A; Mon, 6 Mar 2023 15:29:27 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id ED3EE21E6A1F; Mon, 6 Mar 2023 16:29:26 +0100 (CET) From: Markus Armbruster To: Alex =?utf-8?Q?Benn=C3=A9e?= Cc: marcandre.lureau@redhat.com, qemu-devel@nongnu.org, Beraldo Leal , Eric Blake , Stefan Weil , Paolo Bonzini , Laurent Vivier , "Dr. David Alan Gilbert" , Gerd Hoffmann , Michael Roth , Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= , Markus Armbruster , Daniel P. =?utf-8?Q?Berrang=C3=A9?= , Thomas Huth , Wainer dos Santos Moschetta Subject: Re: [PATCH v3 06/10] monitor: release the lock before calling close() References: <20230207142535.1153722-1-marcandre.lureau@redhat.com> <20230207142535.1153722-7-marcandre.lureau@redhat.com> <87ttz3bi8q.fsf@linaro.org> Date: Mon, 06 Mar 2023 16:29:26 +0100 In-Reply-To: <87ttz3bi8q.fsf@linaro.org> ("Alex =?utf-8?Q?Benn=C3=A9e=22's?= message of "Thu, 02 Mar 2023 09:34:15 +0000") Message-ID: <87ttyxj3u1.fsf@pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/28.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.1 on 10.11.54.8 Received-SPF: pass client-ip=170.10.133.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, 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_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Alex Benn=C3=A9e writes: > marcandre.lureau@redhat.com writes: > >> From: Marc-Andr=C3=A9 Lureau >> >> As per comment, presumably to avoid syscall in critical section. >> >> Fixes: 0210c3b39bef08 ("monitor: Use LOCK_GUARD macros") >> Signed-off-by: Marc-Andr=C3=A9 Lureau > > I know this is already merged but as an academic exercise we could have > kept the lock guard with a little restructuring like this: > > void qmp_closefd(const char *fdname, Error **errp) > { > Monitor *cur_mon =3D monitor_cur(); > mon_fd_t *monfd; > int tmp_fd =3D -1; > > WITH_QEMU_LOCK_GUARD(&cur_mon->mon_lock) { > QLIST_FOREACH(monfd, &cur_mon->fds, next) { No need for QLIST_FOREACH_SAFE(), because .... > if (strcmp(monfd->name, fdname) !=3D 0) { > continue; > } > > QLIST_REMOVE(monfd, next); > tmp_fd =3D monfd->fd; > g_free(monfd->name); > g_free(monfd); > break; ... we break the loop right after modifying the list. Correct? > } > } > > if (tmp_fd > 0) { You mean >=3D > /* close() must be outside critical section */ > close(tmp_fd); > } else { > error_setg(errp, "File descriptor named '%s' not found", fdname= ); This error is new. See also my reply to v4 of this patch. > } If we don't need the new error, we could simply close(tmp_fd); unconditionally. > } > > To my mind it makes it easier to reason about locking but I probably > have an irrational aversion to multiple exit paths for locks. My (possibly irrational) aversion is to if (good) { do some more } else { handle error } I prefer if (!good) { handle error bail out } do some more