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Wed, 25 Sep 2024 07:43:42 +0000 (GMT) Received: from smtpav07.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 454CE20043; Wed, 25 Sep 2024 07:43:42 +0000 (GMT) Received: from [127.0.0.1] (unknown [9.152.108.100]) by smtpav07.fra02v.mail.ibm.com (Postfix) with ESMTP; Wed, 25 Sep 2024 07:43:42 +0000 (GMT) Message-ID: <7164df57c9c3eae2e6f27be7f6c890081740b2cc.camel@linux.ibm.com> Subject: Re: [PATCH 00/18] Stop all qemu-cpu threads on a breakpoint From: Ilya Leoshkevich To: Richard Henderson , Paolo Bonzini , Alex =?ISO-8859-1?Q?Benn=E9e?= , Philippe =?ISO-8859-1?Q?Mathieu-Daud=E9?= Cc: qemu-devel@nongnu.org Date: Wed, 25 Sep 2024 09:43:41 +0200 In-Reply-To: <8c7ed3d0-15c2-426b-baf5-304a984d2559@linaro.org> References: <20240923162208.90745-1-iii@linux.ibm.com> <8c7ed3d0-15c2-426b-baf5-304a984d2559@linaro.org> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.52.4 (3.52.4-1.fc40) X-TM-AS-GCONF: 00 X-Proofpoint-GUID: d1n06rUN4v3cvs8UobQsh3WK5kjq60X6 X-Proofpoint-ORIG-GUID: _A8D7WAOvZX6LdVS78eyZHc6rEChyEKr Content-Transfer-Encoding: quoted-printable X-Proofpoint-UnRewURL: 0 URL was un-rewritten MIME-Version: 1.0 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1051,Hydra:6.0.680,FMLib:17.12.60.29 definitions=2024-09-24_02,2024-09-24_01,2024-09-02_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 mlxscore=0 priorityscore=1501 spamscore=0 adultscore=0 lowpriorityscore=0 impostorscore=0 phishscore=0 clxscore=1015 malwarescore=0 mlxlogscore=463 bulkscore=0 suspectscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.19.0-2408220000 definitions=main-2409250053 Received-SPF: pass client-ip=148.163.158.5; envelope-from=iii@linux.ibm.com; helo=mx0b-001b2d01.pphosted.com X-Spam_score_int: -26 X-Spam_score: -2.7 X-Spam_bar: -- X-Spam_report: (-2.7 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=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 On Tue, 2024-09-24 at 13:46 +0200, Richard Henderson wrote: > On 9/23/24 18:12, Ilya Leoshkevich wrote: > > Hi, > >=20 > > On reporting a breakpoint in a non-non-stop mode, GDB remotes must > > stop > > all threads. Currently qemu-user doesn't do that, breaking the > > debugging session for at least two reasons: concurrent access to > > the > > GDB socket, and an assertion within GDB [1]. > >=20 > > This series fixes this by importing pause_all_vcpus() from qemu- > > system. > > This in turn requires introducing BQL and a few stubs to qemu-user. >=20 > I would have expected you to reuse (some portion of) start_exclusive, > which is already=20 > part of qemu-user.=C2=A0 Is there a reason you chose a solution which > requires... >=20 > > =C2=A0=C2=A0 replay: Add replay_mutex_{lock,unlock}() stubs for qemu-us= er > > =C2=A0=C2=A0 qemu-timer: Provide qemu_clock_enable() stub for qemu-user > > =C2=A0=C2=A0 cpu: Use BQL in qemu-user >=20 > all sorts of other infrastructure? >=20 >=20 > r~ I don't think start_exclusive() would protect the gdb socket from concurrent accesses (e.g., if two threads are simultaneously stopped). I have a patch [1] that introduces a big gdbstub lock for that, but it looks more complex than just extending BQL to qemu-user. Also, the BQL-based pause/resume code already works for the system mode and is well tested. [1] https://gitlab.com/iii-i/qemu/-/commit/0944716218820f8bdfdcf80acc6c39a48b91= 670c