linux-kernel - Re: [PATCH 11/35] media: s2255: Use refcount_t instead of atomic_t for num

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Date: Tue, 23 Apr 2024 13:43:49 +0100
From: Bryan O'Donoghue <bryan.odonoghue@...aro.org>
To: Ricardo Ribalda <ribalda@...omium.org>,
 Martin Tuma <martin.tuma@...iteqautomotive.com>,
 Mauro Carvalho Chehab <mchehab@...nel.org>,
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 <wens@...e.org>, Jernej Skrabec <jernej.skrabec@...il.com>,
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Cc: linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-stm32@...md-mailman.stormreply.com,
 linux-arm-kernel@...ts.infradead.org, linux-staging@...ts.linux.dev,
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Subject: Re: [PATCH 11/35] media: s2255: Use refcount_t instead of atomic_t
 for num_channels

On 15/04/2024 20:34, Ricardo Ribalda wrote:
> Use an API that resembles more the actual use of num_channels.
> 
> Found by cocci:
> drivers/media/usb/s2255/s2255drv.c:2362:5-24: WARNING: atomic_dec_and_test variation before object free at line 2363.
> drivers/media/usb/s2255/s2255drv.c:1557:5-24: WARNING: atomic_dec_and_test variation before object free at line 1558.

Hmm, that commit log needs more detail.

"Convert from atomic_t to refcount_t because refcount_t has memory 
ordering guarantees which atomic does not, hence the WARNING for the 
free after the atomic dec."

Something like that.

I'll leave it up to yourself to decide if this warrants a Fixes:

I don't think so myself because the previous code doesn't seem to matter 
to the decrement and free.

---
bod