linux-kernel - Re: [PATCH v1] devres: Fix devm_krealloc() allocating memory with wrong size

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Date: Sun, 16 Jun 2024 12:17:33 +0200
From: Greg KH <gregkh@...uxfoundation.org>
To: quic_zijuhu <quic_zijuhu@...cinc.com>
Cc: rafael@...nel.org, andriy.shevchenko@...ux.intel.com, brgl@...ev.pl,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] devres: Fix devm_krealloc() allocating memory with
 wrong size

On Sun, Jun 16, 2024 at 06:10:02PM +0800, quic_zijuhu wrote:
> On 6/16/2024 6:02 PM, Greg KH wrote:
> > On Sun, Jun 16, 2024 at 05:54:15PM +0800, Zijun Hu wrote:
> >> Kernel API devm_krealloc() calls alloc_dr() with wrong argument
> >> @total_new_size, and it will cause more memory to be allocated
> >> than required, fixed by using @new_size as alloc_dr()'s argument.
> >>
> >> Fixes: f82485722e5d ("devres: provide devm_krealloc()")
> >> Signed-off-by: Zijun Hu <quic_zijuhu@...cinc.com>
> >> ---
> >>  drivers/base/devres.c | 2 +-
> >>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/base/devres.c b/drivers/base/devres.c
> >> index 3df0025d12aa..1cf87ddf1f55 100644
> >> --- a/drivers/base/devres.c
> >> +++ b/drivers/base/devres.c
> >> @@ -898,7 +898,7 @@ void *devm_krealloc(struct device *dev, void *ptr, size_t new_size, gfp_t gfp)
> >>  	 * taking the lock as most probably the caller uses GFP_KERNEL.
> >>  	 */
> >>  	new_dr = alloc_dr(devm_kmalloc_release,
> >> -			  total_new_size, gfp, dev_to_node(dev));
> >> +			  new_size, gfp, dev_to_node(dev));
> > 
> > Wait, are you sure?  Did you properly test this?  What is the actual
> > savings and how do you handle the fact that you are now not allocating
> > the space reserved for the devres structure itself?
> > 
> sure even if i did not test it.
> beware that alloc_dr() will call check_dr_size() to reserve space for
> devres structure.
> 
> it will reserve the devres structure two times if using wrong
> @total_new_size. it is obvious wrong.

Ah, I missed that, that is tricky.  Please document this better when you
resubmit a new version.

And of course, please test it.

thanks,

greg k-h