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{ "id": 2226560, "url": "http://patchwork.ozlabs.org/api/1.1/covers/2226560/?format=api", "web_url": "http://patchwork.ozlabs.org/project/qemu-devel/cover/20260422161202.34150-1-viking4@gmail.com/", "project": { "id": 14, "url": "http://patchwork.ozlabs.org/api/1.1/projects/14/?format=api", "name": "QEMU Development", "link_name": "qemu-devel", "list_id": "qemu-devel.nongnu.org", "list_email": "qemu-devel@nongnu.org", "web_url": "", "scm_url": "", "webscm_url": "" }, "msgid": "<20260422161202.34150-1-viking4@gmail.com>", "date": "2026-04-22T16:12:01", "name": "[0/1] migration/multifd: fix channel count TOCTOU race on cancel and retry", "submitter": { "id": 92831, "url": "http://patchwork.ozlabs.org/api/1.1/people/92831/?format=api", "name": "Trieu Huynh", "email": "vikingtc4@gmail.com" }, "mbox": "http://patchwork.ozlabs.org/project/qemu-devel/cover/20260422161202.34150-1-viking4@gmail.com/mbox/", "series": [ { "id": 501039, "url": "http://patchwork.ozlabs.org/api/1.1/series/501039/?format=api", "web_url": "http://patchwork.ozlabs.org/project/qemu-devel/list/?series=501039", "date": "2026-04-22T16:12:01", "name": "migration/multifd: fix channel count TOCTOU race on cancel and retry", "version": 1, "mbox": "http://patchwork.ozlabs.org/series/501039/mbox/" } ], "comments": "http://patchwork.ozlabs.org/api/covers/2226560/comments/", "headers": { "Return-Path": "<qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org>", "X-Original-To": "incoming@patchwork.ozlabs.org", "Delivered-To": "patchwork-incoming@legolas.ozlabs.org", "Authentication-Results": [ "legolas.ozlabs.org;\n\tdkim=pass (2048-bit key;\n unprotected) header.d=gmail.com header.i=@gmail.com header.a=rsa-sha256\n header.s=20251104 header.b=cPkWmns+;\n\tdkim-atps=neutral", "legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=nongnu.org\n (client-ip=209.51.188.17; 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helo=mail-pf1-x434.google.com", "X-Spam_score_int": "-17", "X-Spam_score": "-1.8", "X-Spam_bar": "-", "X-Spam_report": "(-1.8 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1,\n DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1,\n FREEMAIL_ENVFROM_END_DIGIT=0.25, FREEMAIL_FROM=0.001,\n RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001,\n 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": "qemu development <qemu-devel.nongnu.org>", "List-Unsubscribe": "<https://lists.nongnu.org/mailman/options/qemu-devel>,\n <mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>", "List-Archive": "<https://lists.nongnu.org/archive/html/qemu-devel>", "List-Post": "<mailto:qemu-devel@nongnu.org>", "List-Help": "<mailto:qemu-devel-request@nongnu.org?subject=help>", "List-Subscribe": "<https://lists.nongnu.org/mailman/listinfo/qemu-devel>,\n <mailto:qemu-devel-request@nongnu.org?subject=subscribe>", "Errors-To": "qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org", "Sender": "qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org" }, "content": "From: Trieu Huynh <vikingtc4@gmail.com>\n\nQEMU aborts on src during multifd migration when multifd-channels is\nchanged after migrate_cancel:\n\n~ # qemu-system-x86_64: ../util/yank.c:107: yank_unregister_instance:\nAssertion `QLIST_EMPTY(&entry->yankfns)' failed.\nAborted (core dumped)\n\nBelow is the backtrace:\n#7 yank_unregister_instance (instance=0x7fffffffd870) at ../util/yank.c:107\n#8 migration_cleanup (s=0x555557649d10) at ../migration/migration.c:1338\n#9 migration_cleanup_bh (opaque=0x555557649d10) at ../migration/migration.c:1345\n#10 migration_bh_dispatch_bh (opaque=0x7ffe500051d0) at ../migration/migration.c:350\n#11 aio_bh_call (bh=0x7ffe5006d670) at ../util/async.c:173\n#12 aio_bh_poll (ctx=0x555557649210) at ../util/async.c:220\n#13 aio_dispatch (ctx=0x555557649210) at ../util/aio-posix.c:390\n#14 aio_ctx_dispatch (source=0x555557649210) at ../util/async.c:365\n...\n\nSteps to reproduce:\n\n* 1. Start VM on src\n./qemu-system-x86_64 \\\n -<other_options>\n\n* 2. Start dest with -incoming defer\n./qemu-system-x86_64 \\\n -incoming defer \\\n -<other_options>\n\n* 3. Enable multifd with 4 channels on both src and dest\n{ \"execute\": \"qmp_capabilities\" }\n{ \"execute\": \"migrate-set-capabilities\",\n \"arguments\": {\"capabilities\": [{\"capability\": \"multifd\",\n \"state\": true}]} }\n{ \"execute\": \"migrate-set-parameters\",\n \"arguments\": {\"multifd-channels\": 4} }\n{ \"execute\": \"migrate-incoming\",\n \"arguments\": {\"uri\": \"tcp:0:4444\"} }\n\n* 4. Trigger migration\n** dest:\n{ \"execute\": \"migrate-incoming\", \"arguments\": {\"uri\": \"tcp:0:4444\"} }\n** src:\n{ \"execute\": \"migrate\", \"arguments\": {\"uri\": \"tcp:127.0.0.1:4444\"} }\n\n* 5. Cancel migration on src while status is active\n{ \"execute\": \"migrate_cancel\" }\n\n* 6. Immediately change multifd-channels to 2 on src\n{ \"execute\": \"migrate-set-parameters\",\n \"arguments\": {\"multifd-channels\": 2} }\n\nQEMU aborts as shown above\n\nTrieu Huynh (1):\n migration/multifd: fix channel count TOCTOU race on cancel and retry\n\n migration/multifd.c | 13 ++++++++-----\n 1 file changed, 8 insertions(+), 5 deletions(-)" }