From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793187776; b=lYDfspdRVyR3esonLopqG8JKYaiEKBsZgV99NrnsY7Jh69z81RL4JjYlYp53Z0Wjky88 kq4X1U/9NGgLuj/ds/v+XzU2cthPJzXA+vefKkAmbCPZSgBgVoJaGaPpZRNvRHzF35yQ6 xJB8Lnzf8IpqAMgBmNZ161H5VddHNRNCvzSeRim3+J29Ojaf/06SVdQs/GVo3jYUiEW6N PKIx3Hiuvk89iiIDxUk167IsjmZYeLB8Umdi857EeKKZL1sTd2o8pvksNT6CpsqzeTFUn FzTCTKEN5zFwXnKVwWlLwNCIUx4Mi+X3J1L5Qr5gkgSfocEqV0djPUOFIPBOKuws52A== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793187776; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: Reply-To:MIME-Version:Lines:X-Developer-Signature:X-Developer-Key: Content-Transfer-Encoding; bh=QViqvSMc9SZmTpJ7o9J/aSlW3YftUq3jgS7tEDNwuGg=; b=sqnjExj2kFPYKC17hBZF6BQl54WJke9C339pTSlsgkLTRPUc5RxMvibZjy4iRmeDF9oc XZQSidAAcA8S2cM6g1V3Xjpo6DCUH8SECyK8ZXfx11Vo4KhJ4tYPvaMNh/r+lii4Ex2vf NaNOAnUABP+fEwZXgCgF6Bm6r4TnkPFwt+5DSzq0tYdr4IE1MBFKoi3j6iHsgUg/YR5Pb 5KMfARk2MNfZK3wTSTx/XuxMFa6LflvV/e0SJ0Xt3G929D25fdHj2RlrLbW4GaqnSRRI2 DEWKVZ4rbSH2HiJO8erIwFTktQBXhpF1GyKLz9dkz2j5mKKTJWeRgJqzBawpM+vq+8A== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b="w/zmQyiq"; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A70E0606A31A for ; Wed, 28 Oct 2026 11:42:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=w/zmQyiq Received: by smtp.kernel.org (Postfix) with ESMTPSA id B95F81F01825; Wed, 28 Oct 2026 11:42:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1793187775; bh=QViqvSMc9SZmTpJ7o9J/aSlW3YftUq3jgS7tEDNwuGg=; h=From:To:Cc:Subject:Date:Reply-To; b=w/zmQyiqoRXUjzVOpY03OzdqdC6kw6s2wg6mA8NVKELcSY67Xw+LKpmKq5mlRE7Fp uD5Eu2/0l1YearXNhgfYW/5FEh1dv1g3mNn1tQ1MdcipQrnPrzZ0F2haCoSC4/Qghi pFtXbsorKmMndhhYAYOQj6q/dT5BBcKPGZWl2NEc= From: Greg Kroah-Hartman To: linux-cve-announce@vger.kernel.org Cc: Greg Kroah-Hartman Subject: CVE-2026-99205: sched/core: Call wakeup_preempt() for queued tasks during class change Date: Wed, 28 Oct 2026 11:36:32 +0100 Message-ID: <2026102814-CVE-2026-99205-e87c@gregkh> X-Mailer: git-send-email 2.56.0 Reply-To: , X-Mailing-List: linux-cve-announce@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=5815; i=gregkh@linuxfoundation.org; h=from:subject:message-id; bh=gBJPzGsNeNSQ3FyXP3ETbrOdnfxJzYcal5mer6nguWc=; b=owGbwMvMwCRo6H6F97bub03G02pJDFkPzz/6sisxJXRdpei6+ZsnbvK0bzLVLk/y21x1oqDwx qFGoYjrHbEsDIJMDLJiiixftvEc3V9xSNHL0PY0zBxWJpAhDFycAjCRTYIMC6Z7tIYxrZ8r6/H1 AWP13P938jjv72JYsGNtfPFWw8anXtITvqeJMoWxaPjbAQA= X-Developer-Key: i=gregkh@linuxfoundation.org; a=openpgp; fpr=F4B60CC5BF78C2214A313DCB3147D40DDB2DFB29 Content-Transfer-Encoding: 8bit From: Greg Kroah-Hartman Description =========== In the Linux kernel, the following vulnerability has been resolved: sched/core: Call wakeup_preempt() for queued tasks during class change Paul reported recent RCU changes exposed a lost resched where CPU idles with a rcutorture thread waiting while being completely runnable. Dumping the rq state at the time of idling with runnable tasks showed the following: rq->next_class = &fair_sched_class rq->nr_running = 1 rq->cfs.h_nr_queued = 0 rq->rt.rt_nr_running = 1 Although the waiting task was an RT task, "rq->next_class" did not point to rt_sched_class and was stuck at the lower priority fair_sched_class. Inspecting sched_change_end() revealed the following race with __sched_setscheduler() for queued, but non-running tasks: CPU0 CPU1 ==== ==== __schedule() /* * rq->donor is a fair task that blocks. * rq->next_class = &fair_sched_class */ rq_lock(rq0) pick_next_task() /* nr_running = 0 */ pick_task_fair() sched_balance_newidle() raw_spin_rq_unlock(rq0) rq_lock(rq0) activate_task(rq0, p) /* p is a fair task */ rq0->nr_running++; rq0->cfs.h_nr_queued++; wakeup_preempt(rq, p) rq->next_class = &fair_sched_class resched_curr() rq_unlock(rq0) __sched_setscheduler(p) /* p is moved to SCHED_RR */ task_rq_lock(p) sched_change_begin() rq0->cfs.h_nr_queued--; rq0->rt.rt_nr_running++; sched_change_end() /* * p->on_rq = 1 (ctx->queued) * but p is not rq->donor * (!ctx->running) hence * resched_curr() is and * rq->next_class upgrade is * skipped. */ task_rq_unlock() raw_spin_rq_lock(rq0) /* * rq->nr_running = 1 * rq->cfs.h_nr_queued = 0 * rq->rt.rt_nr_running = 1 * rq->next_class = &fair_sched_class */ if (rq->cfs.h_nr_queued && ...) /* Above is false */ if (rq_modified_above(this_rq, &fair_sched_class)) /* Also false since rq->next_class is still fair */ /* * sched_balance_newidle() is considered to * have failed to pull any fair tasks and no * other wakeups were detected. */ return NULL; /* pick_task_fair() */ pick_task_idle() return rq->idle; next = rq->idle; /* Preemption indicators are lost */ clear_tsk_need_resched(prev); clear_preempt_need_resched(); rq->curr = rq->idle; !!! rq->idle switches in with rq->running == 1 but !need_resched() !!! In simple words, enqueue, followed by a class change of the newly queued task goes unnoticed in rq->next_class indicator and sched_balance_newidle() sees no fair task, nor any higher priority task enqueued. The above sequence will lead to CPU idling with a runnable task on the CPU. Call wakeup_preempt() for ctx->queued cases in sched_change_end() to re-evaluate rq->next_class after class change (ENQUEUE_CLASS) and set the NEED_RESCHED indicator accordingly. Newidle balance will correctly see an enqueue of a higher priority task if a queued task was upgraded when the rq_lock() was dropped and will retry the pick. The Linux kernel CVE team has assigned CVE-2026-99205 to this issue. Affected and fixed versions =========================== Issue introduced in 7.0 with commit 704069649b5bfb7bf1fe32c0281fe9036806a59a and fixed in 7.2.13 with commit ae89744c5ebf299bf55ac7581768fbd9f119a903 Issue introduced in 7.0 with commit 704069649b5bfb7bf1fe32c0281fe9036806a59a and fixed in 7.3 with commit 118a2cf4ced60777a2408001e2b4838fed1cea55 Please see https://www.kernel.org for a full list of currently supported kernel versions by the kernel community. Unaffected versions might change over time as fixes are backported to older supported kernel versions. The official CVE entry at https://cve.org/CVERecord/?id=CVE-2026-99205 will be updated if fixes are backported, please check that for the most up to date information about this issue. Affected files ============== The file(s) affected by this issue are: kernel/sched/core.c Mitigation ========== The Linux kernel CVE team recommends that you update to the latest stable kernel version for this, and many other bugfixes. Individual changes are never tested alone, but rather are part of a larger kernel release. Cherry-picking individual commits is not recommended or supported by the Linux kernel community at all. If however, updating to the latest release is impossible, the individual changes to resolve this issue can be found at these commits: https://git.kernel.org/stable/c/ae89744c5ebf299bf55ac7581768fbd9f119a903 https://git.kernel.org/stable/c/118a2cf4ced60777a2408001e2b4838fed1cea55