linux-kernel - Re: [PATCH] [v2] drm/i915/pmu: avoid -Wmaybe-uninitialized warning

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Date:   Tue, 13 Mar 2018 16:38:11 +0000
From:   Chris Wilson <chris@...is-wilson.co.uk>
To:     Arnd Bergmann <arnd@...db.de>,
        "Jani Nikula" <jani.nikula@...ux.intel.com>,
        "Joonas Lahtinen" <joonas.lahtinen@...ux.intel.com>,
        "Rodrigo Vivi" <rodrigo.vivi@...el.com>,
        "David Airlie" <airlied@...ux.ie>
Cc:     "Arnd Bergmann" <arnd@...db.de>,
        "Tvrtko Ursulin" <tvrtko.ursulin@...el.com>,
        "Michal Wajdeczko" <michal.wajdeczko@...el.com>,
        intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] [v2] drm/i915/pmu: avoid -Wmaybe-uninitialized warning

Quoting Arnd Bergmann (2018-03-13 16:19:31)
> The conditional spinlock confuses gcc into thinking the 'flags' value
> might contain uninitialized data:
> 
> drivers/gpu/drm/i915/i915_pmu.c: In function '__i915_pmu_event_read':
> arch/x86/include/asm/paravirt_types.h:573:3: error: 'flags' may be used uninitialized in this function [-Werror=maybe-uninitialized]
> 
> The code is correct, but it's easy to see how the compiler gets confused
> here. This avoids the problem by pulling the lock outside of the function
> into its only caller.
> 
> Fixes: 1fe699e30113 ("drm/i915/pmu: Fix sleep under atomic in RC6 readout")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
Reviewed-by: Chris Wilson <chris@...is-wilson.co.uk>
-Chris