From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=91.218.175.17 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794495010; b=Q2A2/zYwxuUSVg9+N3PNIC5GfqW1lkZ3X4zwKyl77v/9L2sot3vE9ONmk63/Z0cRSXiy D7W2nCyYei4ArB5mus7zTeAHnhV8+Rb6vJ1onUmvMTGVBJhrukHbe1CdmosO5Z1lG0T3T rYLVsIQwrx/dC/lFo9ZyoCKkeStgfmxyfyBLBVWrF0EqZC1sDlJs9nZlbmQSE/epYWNbn hAMauaErRaGp/6FSJYhLu0j1GhAZDcPPQ1mTB6wllmImMHpDyiQbJL6yFNxaPj2kn8len IvWCAVC8kLk639/83/DroUnNPmvSD1N/iqSe6gayGYF2BDYCFNS/68YvEtYhc/MzUEA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794495010; h=DMARC-Filter:X-Envelope-To:DKIM-Signature:X-Envelope-To:Received: X-Mizu-Trace-ID:X-Migadu-Flow:From:To:Cc:Subject:Date:Message-ID: X-Mailer:In-Reply-To:References:MIME-Version: Content-Transfer-Encoding; bh=fKhNVS4HIbJOghQyFAYDyIQH4s/FReGVb6zBWdLmzR4=; b=To1dyiJU7qTRteQyt/0RsXEbiRfuILMY7mbi0+BucSIM7LuXk74zcSEqx0zyAC3slDxz hns8UnPU87dI6tR2eu1RLllcJHuCWjsXEleKam65bD3iuZa+9eOxi2AQ3X2sEurMe1aUD 7xy893olb1LNHvTulGnD9WIbI5+TefatYLLjQV+eD24zKTMLvyb/TAoqmqwzZa1SL+Mry 6CCgkU76SqMSkP3KD3zSq0vHJD031lbCH4hGsFOM8MZ+zRnP1xLUJVkDOPTqzQ1rRDHeZ z9yFFG/aEX4XQ57xA+jJc/C2cABqSG/9d5f6Zj3VHtXkf6urvKDpYJG9NU7ctEbldDw== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=VgtrlgrF; arc=none smtp.remote-ip=91.218.175.17 Received: from mta0.migadu.com (out-17.mta0.migadu.com [91.218.175.17]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2FE5C606A32D for ; Thu, 12 Nov 2026 14:50:09 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org 2FE5C606A32D Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=VgtrlgrF X-Envelope-To: bpf@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=KG9+P7EeigIaTfG3TpucRpnUPoNln70sSanoxbchnvI=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1794495008; v=1; x=1795099808; b=VgtrlgrFSZRND/KG4Eiwkv/bvfUqhpJO9HtTOyyU2ZShdzTQGoTCcXtWQB9TKFwGv816ydHf aGyhKJmmL2LAxiswRs7ymGAmCsLKG1sQzMrmKpPJ+rOMkvowXZC9tc7FkFudeh8+IqvA09kIm8/ bIaeCjR5iifzkXJK6jYinMXI= X-Envelope-To: bpf@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id 58f4540b9f06cb52; Thu, 12 Nov 2026 14:50:06 +0000 X-Mizu-Trace-ID: 58f4540b9f06cb52 X-Migadu-Flow: FLOW_OUT From: Tao Cui To: tj@kernel.org Cc: void@manifault.com, arighi@nvidia.com, changwoo@igalia.com, mingo@redhat.com, peterz@infradead.org, sched-ext@lists.linux.dev, linux-kernel@vger.kernel.org, bpf@vger.kernel.org, cui.tao@linux.dev, Tao Cui Subject: [PATCH 2/2] sched_ext: Block a retained donor before PI deboost routes it back to sched_ext Date: Thu, 12 Nov 2026 22:49:35 +0800 Message-ID: <20261112144935.583937-3-cui.tao@linux.dev> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20261112144935.583937-1-cui.tao@linux.dev> References: <20261112144935.583937-1-cui.tao@linux.dev> X-Mailing-List: bpf@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Tao Cui rt_mutex_setprio() is the only entry path into sched_ext that does not block a retained donor: an ext task PI-boosted by an rt waiter can block on a second kernel mutex while boosted, and on deboost is routed back to sched_ext carrying the queued+blocked state that scx_prepare_setscheduler() promises never happens; every PI cycle hands the BPF scheduler a queued+blocked donor it never admitted. Call scx_prepare_task_sched_change() before the sched_change guard when the class change routes the task back to sched_ext, which performs the missing sched_proxy_block_task() (plus an update_rq_clock() that is harmless here: the clock was already advanced, so the second advance only applies a small delta). The boost direction (ext -> rt) needs no handling. Fixes: be8be8acb268 ("sched_ext: Block proxy donors before taking control") Signed-off-by: Tao Cui --- kernel/sched/core.c | 12 ++++++++++++ kernel/sched/ext/ext.h | 2 ++ 2 files changed, 14 insertions(+) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index f7a452123ef5..dcb16b006740 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -7816,6 +7816,18 @@ void rt_mutex_setprio(struct task_struct *p, struct task_struct *pi_task) if (prev_class != next_class) queue_flag |= DEQUEUE_CLASS; + /* + * PI boost can route @p out of sched_ext: policy stays SCHED_EXT but + * __setscheduler_class() follows the effective rt prio, and rt/fair + * may have retained @p on the rq as a blocked donor. Block it before + * sched_change_begin() records the queued state, the same way the + * other entry points into sched_ext do. + */ +#ifdef CONFIG_SCHED_CLASS_EXT + if ((queue_flag & DEQUEUE_CLASS) && next_class == &ext_sched_class) + scx_prepare_task_sched_change(p); +#endif + scoped_guard (sched_change, p, queue_flag) { /* * Boosting condition are: diff --git a/kernel/sched/ext/ext.h b/kernel/sched/ext/ext.h index d32bc01071b0..1a699be25331 100644 --- a/kernel/sched/ext/ext.h +++ b/kernel/sched/ext/ext.h @@ -19,6 +19,7 @@ void scx_rq_activate(struct rq *rq); void scx_rq_deactivate(struct rq *rq); int scx_check_setscheduler(struct task_struct *p, int policy); void scx_prepare_setscheduler(struct task_struct *p, int policy); +void scx_prepare_task_sched_change(struct task_struct *p); bool task_should_scx(int policy); bool scx_allow_ttwu_queue(const struct task_struct *p); bool __scx_allow_proxy_exec(const struct task_struct *p); @@ -72,6 +73,7 @@ static inline void scx_rq_activate(struct rq *rq) {} static inline void scx_rq_deactivate(struct rq *rq) {} static inline int scx_check_setscheduler(struct task_struct *p, int policy) { return 0; } static inline void scx_prepare_setscheduler(struct task_struct *p, int policy) {} +static inline void scx_prepare_task_sched_change(struct task_struct *p) {} static inline bool task_on_scx(const struct task_struct *p) { return false; } static inline bool scx_allow_ttwu_queue(const struct task_struct *p) { return true; } static inline bool scx_allow_proxy_exec(const struct task_struct *p) { return true; } -- 2.53.0 base-commit: 5b740a72b55c4267ba4d8010f17dde26b26f52d3