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Wed, 15 Jan 2025 11:05:13 -0800 (PST) X-Google-Smtp-Source: AGHT+IH9lrBcPfHS079Mcedf4reDWCRUrvEEohimeIyr++zSjZUNT9GeY4kByFU016uSBG0S5wrR/A== X-Received: by 2002:a05:600c:4f4e:b0:436:1ac2:1acf with SMTP id 5b1f17b1804b1-436e26e28cemr271163475e9.20.1736967913210; Wed, 15 Jan 2025 11:05:13 -0800 (PST) Received: from [192.168.10.3] ([176.206.124.70]) by smtp.googlemail.com with ESMTPSA id ffacd0b85a97d-38a8e38c1d6sm18690132f8f.50.2025.01.15.11.05.11 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 15 Jan 2025 11:05:12 -0800 (PST) Message-ID: <8dff3836-1c96-4ae8-a9d8-f86f97d78986@redhat.com> Date: Wed, 15 Jan 2025 20:05:07 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] system/runstate: Fix regression, clarify BQL status of exit notifiers To: Phil Dennis-Jordan , qemu-devel@nongnu.org Cc: philmd@linaro.org, akihiko.odaki@daynix.com, dwmw2@infradead.org References: <20250112212609.17996-1-phil@philjordan.eu> From: Paolo Bonzini Content-Language: en-US Autocrypt: addr=pbonzini@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=pbonzini@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -39 X-Spam_score: -4.0 X-Spam_bar: ---- X-Spam_report: (-4.0 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.141, 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=-1.793, 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 1/12/25 22:26, Phil Dennis-Jordan wrote: > By changing the way the main QEMU event loop is invoked, I inadvertently > changed the BQL status of exit notifiers: some of them implicitly > assumed they would be called with the BQL held; the BQL is however > not held during the exit(status) call in qemu_default_main(). > > Instead of attempting to ensuring we always call exit() from the BQL - > including any transitive calls - this change adds a BQL lock guard to > qemu_run_exit_notifiers, ensuring the BQL will always be held in the > exit notifiers. > > Additionally, the BQL promise is now documented at the > qemu_{add,remove}_exit_notifier() declarations. > > Fixes: f5ab12caba4f ("ui & main loop: Redesign of system-specific main > thread event handling") > Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2771 > Reported-by: David Woodhouse > Signed-off-by: Phil Dennis-Jordan I'm worried that this breaks for exit() calls that happen within a BQL-taken area (for example, anything that uses error_fatal) due to... void bql_lock_impl(const char *file, int line) { QemuMutexLockFunc bql_lock_fn = qatomic_read(&bql_mutex_lock_func); g_assert(!bql_locked()); // <--- this bql_lock_fn(&bql, file, line); set_bql_locked(true); } Paolo