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Date: Mon, 9 Mar 2026 17:56:34 +0100
From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: Josh Law <hlcj1234567@gmail.com>
Cc: linux-staging@lists.linux.dev, linux-kernel@vger.kernel.org,
	Josh Law <objecting@objecting.org>
Subject: Re: [PATCH] staging: axis-fifo: minimize lock duration in write
Message-ID: <2026030903-although-gratitude-49a6@gregkh>
References: <20260301005836.2513391-1-objecting@objecting.org>
 <2026030914-task-stunned-21e0@gregkh>
 <07e2ae8e-e6e9-4def-9eb2-2c48ce6669b8@gmail.com>
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On Mon, Mar 09, 2026 at 04:11:25PM +0000, Josh Law wrote:
> 9 Mar 2026 16:07:50 Greg Kroah-Hartman <gregkh@linuxfoundation.org>:
> 
> > On Sun, Mar 01, 2026 at 12:58:36AM +0000, Josh Law wrote:
> >> Memory allocation and copy from user space with vmemdup_user() is relatively slow and can sleep. Move it outside the lock to minimize the time the mutex is held, reducing contention for concurrent accesses.
> >
> > Something happened with your line wrapping :(
> >
> > And are you sure that your change works?  What is wrong with grabbing
> > the lock this way?
> >
> > thanks,
> >
> > greg k-h
> 
> The issue with grabbing the lock before vmemdup_user() is that the allocation and user-space copy can take a significant amount of time and can sleep.

But what is wrong with that?

> Also, it's just to be more efficient haha, and yes I'm sure this change works, I own the hardware, and it operates better...

Great, please put the performance numbers in the patch, that will show
the need for this change.

thanks,

greg k-h