From: Tomi Valkeinen <tomi.valkeinen@ti.com>
To: "Ville Syrjälä" <ville.syrjala@linux.intel.com>
Cc: Archit Taneja <archit@ti.com>,
linux-omap@vger.kernel.org, linux-fbdev@vger.kernel.org
Subject: Re: [PATCH 2/5] OMAPFB: simplify locking
Date: Fri, 07 Dec 2012 13:42:10 +0000 [thread overview]
Message-ID: <50C1F232.80508@ti.com> (raw)
In-Reply-To: <20121207125350.GE32230@intel.com>
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On 2012-12-07 14:53, Ville Syrjälä wrote:
> On Fri, Dec 07, 2012 at 01:55:06PM +0200, Tomi Valkeinen wrote:
>> Kernel lock verification code has lately detected possible circular
>> locking in omapfb. The exact problem is unclear, but omapfb's current
>> locking seems to be overly complex.
>>
>> This patch simplifies the locking in the following ways:
>>
>> - Remove explicit omapfb mem region locking. I couldn't figure out the
>> need for this, as long as we take care to take omapfb lock.
>
> I suppose the idea with that was that you wouldn't need the global
> omapfb lock, and also it was an rwsem so it allowed parallel access to
> the mem regions, unless the region size was being changed, in which
> case it took the write lock. I can't really remember what the reason
> for using an rwsem was, but I suppose there was one at the time.
Right. Yes, I have no recollection either of the possible reason for it
=). Did we have multiple concurrerent users for the fbs? It still sounds
like a useless optimization, as all the region locks were only held for
a short time, as far as I saw.
It could also be that we're missing something from the mainline kernel,
which we had in the Nokia kernel, and which would explain the need for
region locks.
> I think the only correctness issue with your patch is that you're
> opening up a race between omapfb_mmap and
> omapfb_setup_mem/store_size.
Good point. I think this can be fixed by taking fb_info->mm_lock in
omapfb_setup_mem & co.
Tomi
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next prev parent reply other threads:[~2012-12-07 13:42 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-12-07 11:55 [PATCH 1/5] OMAPFB: remove exported udpate window Tomi Valkeinen
2012-12-07 11:55 ` [PATCH 2/5] OMAPFB: simplify locking Tomi Valkeinen
2012-12-07 12:53 ` Ville Syrjälä
2012-12-07 13:42 ` Tomi Valkeinen [this message]
2012-12-07 14:16 ` Tomi Valkeinen
2012-12-07 14:45 ` Ville Syrjälä
2012-12-13 11:17 ` Tomi Valkeinen
2012-12-07 11:55 ` [PATCH 3/5] OMAPFB: remove warning when trying to alloc at certain paddress Tomi Valkeinen
2012-12-07 11:55 ` [PATCH 4/5] OMAPDSS: manage output-dssdev connection in output drivers Tomi Valkeinen
2012-12-07 11:55 ` [PATCH 5/5] OMAPFB: connect ovl managers to all dssdevs Tomi Valkeinen
2012-12-10 7:46 ` Archit Taneja
2012-12-10 8:03 ` Tomi Valkeinen
2012-12-10 9:55 ` Archit Taneja
2012-12-10 10:07 ` Tomi Valkeinen
2012-12-10 10:54 ` Archit Taneja
2012-12-10 11:03 ` Tomi Valkeinen
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