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From: "Luck, Tony" <tony.luck@intel.com>
To: "Chatre, Reinette" <reinette.chatre@intel.com>,
	Borislav Petkov <bp@alien8.de>
Cc: "Yu, Fenghua" <fenghua.yu@intel.com>,
	"Wieczor-Retman, Maciej" <maciej.wieczor-retman@intel.com>,
	Peter Newman <peternewman@google.com>,
	James Morse <james.morse@arm.com>,
	Babu Moger <babu.moger@amd.com>,
	"Drew Fustini" <dfustini@baylibre.com>,
	"x86@kernel.org" <x86@kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"patches@lists.linux.dev" <patches@lists.linux.dev>
Subject: RE: [PATCH] x86/resctrl: Fix mbm_setup_overflow_handler() when last CPU goes offline
Date: Wed, 27 Mar 2024 23:01:10 +0000	[thread overview]
Message-ID: <SJ1PR11MB6083F3AB8069CCDC7DB5004BFC342@SJ1PR11MB6083.namprd11.prod.outlook.com> (raw)
In-Reply-To: <c53d6abd-5dbe-4edf-89c0-abbea0df1f1c@intel.com>

> There seems to be two issues here (although I am not familiar with these flows). First,
> it seems that tick_nohz_full_mask is not actually allocated unless the user boots
> with a "nohz_full=". This means that any attempt to access bits within tick_nohz_full_mask
> will cause this OOPS. If that is allocated then the second issue seems that the  
> buried __ffs() call requires that it not be called with 0 and this checking is not done.
>
> To me it seems most appropriate to fix this at the central place to ensure all scenarios
> are handled instead of scattering checks.

Good analysis.

> To that end, what do you think of something like below? It uses tick_nohz_full_enabled() check
> to ensure that tick_nohz_full_mask is actually allocated while the other changes aim to
> avoid __ffs() on 0.

Looks good.

Tested-by: Tony Luck <tony.luck@intel.com>
Reviewed-by: Tont Luck <tony.luck@intel.com>

-Tony

  reply	other threads:[~2024-03-27 23:01 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2024-03-27 18:46 [PATCH] x86/resctrl: Fix mbm_setup_overflow_handler() when last CPU goes offline Tony Luck
2024-03-27 22:37 ` Reinette Chatre
2024-03-27 23:01   ` Luck, Tony [this message]
2024-03-28 21:11     ` Reinette Chatre

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