From nobody Thu Dec 18 22:06:15 2025 Received: from smtpout.efficios.com (smtpout.efficios.com [158.69.130.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D427C2BD1D for ; Tue, 3 Dec 2024 16:36:16 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=158.69.130.18 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1733243778; cv=none; b=S1oA8Qe/r0jtx41MtyiqBvz5GP4SDDVvgSpNv1mpUGiaAfRYCCBGlQMjSDZpUCneDSGZd/rUUOrQg6B99MLb/MtuWwSnhtoeERsMGrwgSkmPxjCke10IrjC3dn7dpZL6eWufZunXcJw5DIftJK40l+n7xKgPb+dzKdrHg9iwAG4= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1733243778; c=relaxed/simple; bh=tmo9AAA6kt3XzX9tU+vZGSa3qOh7lMibgecPzC2J+EE=; h=From:To:Cc:Subject:Date:Message-Id:MIME-Version; b=RgDllqJvz2wvm6h8yHqRk18DyvtxPK2ygZMDxFRHBGRCZVgvF8PToxoRNW9iodpZvoEWY3Bj6s0jfx4s/cMU8i95P5F7sU8dkkH9okQ8yfPBVKIIFIAOE4kR4fCmzHPHB3MM/GqNwQX+n7KabU3MQJh2Z+DZYxaaplpxDQWmcao= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=efficios.com; spf=pass smtp.mailfrom=efficios.com; dkim=pass (2048-bit key) header.d=efficios.com header.i=@efficios.com header.b=p3dMMQkd; arc=none smtp.client-ip=158.69.130.18 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=efficios.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=efficios.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=efficios.com header.i=@efficios.com header.b="p3dMMQkd" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=efficios.com; s=smtpout1; t=1733243775; bh=tmo9AAA6kt3XzX9tU+vZGSa3qOh7lMibgecPzC2J+EE=; h=From:To:Cc:Subject:Date:From; b=p3dMMQkdsss9ny2ZTrzW815KyzQMqerq+5slZOnznX7vlWqbUF0877Yw/R0rrZuxV mswNZZc8lZk2gfLAfE5b8IdC6JgfsOEEhuLaTcsHYfWtRq/Lyij27mBqlRSIOKgYr4 yi0IHyfasRzbIz4aY+zkRxwXHGVU2mkB8QwsocBJfTKphUqDbhCqiMyk9nl2PdppsX RB8fEIyknlS0l8PEu1d9y/J2BYo23cdM50BOQ3p+piN6SEFem5Iy+6SElmY8Ud8aCt pWDtcbGNI1gHUa2XR0vhUMsdhXrXMy+bOxQZUe6EaexhXtOULThRF0EBRhsewmyE7e PD8goAJDw/RuA== Received: from thinkos.internal.efficios.com (96-127-217-162.qc.cable.ebox.net [96.127.217.162]) by smtpout.efficios.com (Postfix) with ESMTPSA id 4Y2mW33sGWzTbr; Tue, 3 Dec 2024 11:36:15 -0500 (EST) From: Mathieu Desnoyers To: Rik van Riel Cc: linux-kernel@vger.kernel.org, Mathieu Desnoyers , Peter Zijlstra , Ingo Molnar , Dave Hansen , Linus Torvalds , Mel Gorman , x86@kernel.org Subject: [RFC PATCH] smp: Evaluate local cond_func() before IPI side-effects Date: Tue, 3 Dec 2024 11:35:58 -0500 Message-Id: <20241203163558.3455535-1-mathieu.desnoyers@efficios.com> X-Mailer: git-send-email 2.39.5 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" In smp_call_function_many_cond(), the local cond_func() is evaluated after triggering the remote CPU IPIs. If cond_func() depends on loading shared state updated by other CPU's IPI handlers func(), then triggering execution of remote CPUs IPI before evaluating cond_func() may have unexpected consequences. One example scenario is evaluating a jiffies delay in cond_func(), which is updated by func() in the IPI handlers. This situation can prevent execution of periodic cleanup code on the local CPU. Link: https://lore.kernel.org/lkml/20241202202213.26a79ed6@fangorn/ Signed-off-by: Mathieu Desnoyers Cc: Rik van Riel Cc: Peter Zijlstra Cc: Ingo Molnar Cc: Dave Hansen Cc: Linus Torvalds Cc: Mel Gorman Cc: x86@kernel.org Reviewed-by: Rik van Riel --- kernel/smp.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/kernel/smp.c b/kernel/smp.c index 27dc31a146a3..f104c8e83fc4 100644 --- a/kernel/smp.c +++ b/kernel/smp.c @@ -815,7 +815,8 @@ static void smp_call_function_many_cond(const struct cp= umask *mask, WARN_ON_ONCE(!in_task()); =20 /* Check if we need local execution. */ - if ((scf_flags & SCF_RUN_LOCAL) && cpumask_test_cpu(this_cpu, mask)) + if ((scf_flags & SCF_RUN_LOCAL) && cpumask_test_cpu(this_cpu, mask) && + (!cond_func || cond_func(this_cpu, info))) run_local =3D true; =20 /* Check if we need remote execution, i.e., any CPU excluding this one. */ @@ -868,7 +869,7 @@ static void smp_call_function_many_cond(const struct cp= umask *mask, send_call_function_ipi_mask(cfd->cpumask_ipi); } =20 - if (run_local && (!cond_func || cond_func(this_cpu, info))) { + if (run_local) { unsigned long flags; =20 local_irq_save(flags); --=20 2.39.5