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Wed, 08 Jan 2025 21:50:47 -0800 (PST) From: Akihiko Odaki Date: Thu, 09 Jan 2025 14:50:21 +0900 Subject: [PATCH v7 2/2] memory: Do not create circular reference with subregion MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Message-Id: <20250109-san-v7-2-93c432a73024@daynix.com> References: <20250109-san-v7-0-93c432a73024@daynix.com> In-Reply-To: <20250109-san-v7-0-93c432a73024@daynix.com> To: Eduardo Habkost , Marcel Apfelbaum , =?utf-8?q?Philippe_Mathieu-Daud=C3=A9?= , Yanan Wang , John Snow , BALATON Zoltan , Jiaxun Yang , Nicholas Piggin , Daniel Henrique Barboza , David Gibson , Harsh Prateek Bora , Alexey Kardashevskiy , "Michael S. Tsirkin" , =?utf-8?q?Alex_Benn=C3=A9e?= , Peter Xu , Fabiano Rosas , Paolo Bonzini , David Hildenbrand , Thomas Huth , Laurent Vivier , Peter Maydell Cc: qemu-devel@nongnu.org, qemu-block@nongnu.org, qemu-ppc@nongnu.org, devel@daynix.com, Akihiko Odaki X-Mailer: b4 0.14-dev-fd6e3 Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=2607:f8b0:4864:20::102c; envelope-from=akihiko.odaki@daynix.com; helo=mail-pj1-x102c.google.com X-Spam_score_int: -18 X-Spam_score: -1.9 X-Spam_bar: - X-Spam_report: (-1.9 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable 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+importer=patchew.org@nongnu.org Sender: qemu-devel-bounces+importer=patchew.org@nongnu.org X-ZohoMail-DKIM: pass (identity @daynix-com.20230601.gappssmtp.com) X-ZM-MESSAGEID: 1736401895467116600 memory_region_update_container_subregions() used to call memory_region_ref(), which creates a reference to the owner of the subregion, on behalf of the owner of the container. This results in a circular reference if the subregion and container have the same owner. memory_region_ref() creates a reference to the owner instead of the memory region to match the lifetime of the owner and memory region. We do not need such a hack if the subregion and container have the same owner because the owner will be alive as long as the container is. Therefore, create a reference to the subregion itself instead ot its owner in such a case; the reference to the subregion is still necessary to ensure that the subregion gets finalized after the container. Signed-off-by: Akihiko Odaki Reviewed-by: Peter Xu --- system/memory.c | 24 ++++++++++++++++++++++-- 1 file changed, 22 insertions(+), 2 deletions(-) diff --git a/system/memory.c b/system/memory.c index 78e17e0efa83..972617b0192d 100644 --- a/system/memory.c +++ b/system/memory.c @@ -1855,6 +1855,24 @@ void memory_region_unref(MemoryRegion *mr) } } =20 +static void memory_region_ref_subregion(MemoryRegion *subregion) +{ + if (subregion->container->owner =3D=3D subregion->owner) { + object_ref(OBJECT(subregion)); + } else { + memory_region_ref(subregion); + } +} + +static void memory_region_unref_subregion(MemoryRegion *subregion) +{ + if (subregion->container->owner =3D=3D subregion->owner) { + object_unref(OBJECT(subregion)); + } else { + memory_region_unref(subregion); + } +} + uint64_t memory_region_size(MemoryRegion *mr) { if (int128_eq(mr->size, int128_2_64())) { @@ -2644,7 +2662,8 @@ static void memory_region_update_container_subregions= (MemoryRegion *subregion) =20 memory_region_transaction_begin(); =20 - memory_region_ref(subregion); + memory_region_ref_subregion(subregion); + QTAILQ_FOREACH(other, &mr->subregions, subregions_link) { if (subregion->priority >=3D other->priority) { QTAILQ_INSERT_BEFORE(other, subregion, subregions_link); @@ -2702,7 +2721,8 @@ void memory_region_del_subregion(MemoryRegion *mr, assert(alias->mapped_via_alias >=3D 0); } QTAILQ_REMOVE(&mr->subregions, subregion, subregions_link); - memory_region_unref(subregion); + memory_region_unref_subregion(subregion); + memory_region_update_pending |=3D mr->enabled && subregion->enabled; memory_region_transaction_commit(); } --=20 2.47.1