Re: [Outreachy kernel] [PATCH] staging: netlogic: Remove unnecessary error print

From: Julia Lawall <julia.lawall@lip6.fr>
To: Himadri Pandya <himadri18.07@gmail.com>
Cc: Greg KH <gregkh@linuxfoundation.org>, outreachy-kernel@googlegroups.com
Subject: Re: [Outreachy kernel] [PATCH] staging: netlogic: Remove unnecessary error print
Date: Thu, 21 Mar 2019 11:42:59 +0100 (CET)	[thread overview]
Message-ID: <alpine.DEB.2.20.1903211141480.5292@hadrien> (raw)
In-Reply-To: <CAPnhUpaXwEBMFa_ukU9uauFuEaUojMju_kG+WHnJ9SQcAXrSpA@mail.gmail.com>

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On Thu, 21 Mar 2019, Himadri Pandya wrote:

>
>
> On Thu, Mar 21, 2019 at 3:38 PM Julia Lawall <julia.lawall@lip6.fr> wrote:
>
>
>       On Thu, 21 Mar 2019, Himadri Pandya wrote:
>
>       > Kmalloc normally produces a backtrace when there is not enough memory.
>       > So it is unnecessary to print an error message that provides only this
>       > information. Hence, remove pr_error() from memory allocation check.
>       > Issue found using Coccinelle.
>       >
>       > Signed-off-by: Himadri Pandya <himadri18.07@gmail.com>
>       > ---
>       >ï¿œ drivers/staging/netlogic/xlr_net.c | 4 +---
>       >ï¿œ 1 file changed, 1 insertion(+), 3 deletions(-)
>       >
>       > diff --git a/drivers/staging/netlogic/xlr_net.c b/drivers/staging/netlogic/xlr_net.c
>       > index 8554fcf4321b..afba1248e100 100644
>       > --- a/drivers/staging/netlogic/xlr_net.c
>       > +++ b/drivers/staging/netlogic/xlr_net.c
>       > @@ -389,10 +389,8 @@ static void *xlr_config_spill(struct xlr_net_priv *priv, int reg_start_0,
>       >ï¿œ ï¿œ ï¿œ ï¿œbase = priv->base_addr;
>       >ï¿œ ï¿œ ï¿œ ï¿œspill_size = size;
>       >ï¿œ ï¿œ ï¿œ ï¿œspill = kmalloc(spill_size + SMP_CACHE_BYTES, GFP_ATOMIC);
>       > -ï¿œ ï¿œ ï¿œif (!spill) {
>       > -ï¿œ ï¿œ ï¿œ ï¿œ ï¿œ ï¿œ ï¿œpr_err("Unable to allocate memory for spill area!\n");
>       > +ï¿œ ï¿œ ï¿œif (!spill)
>       >ï¿œ ï¿œ ï¿œ ï¿œ ï¿œ ï¿œ ï¿œ ï¿œreturn ZERO_SIZE_PTR;
>
>       This seems to be the only driver that uses ZERO_SIZE_PTR as the result for
>       kmalloc.ï¿œ It could be worth looking into what happens to this value
>       afterwards.
>
>       julia
>
>
> This is interesting. Later the pointer spillï¿œis aligned withï¿œSMP_CACHE_BYTES (which is defined using L1_CACHE_BYTES).ï¿œï¿œAs per my understanding,ï¿œxlr_config_spill() returns ZERO_SIZE_PTR if kmalloc()ï¿œcannot allocate sufficient
> memory(equivalent to spill_size) as the return value is being used to configure network accelerator's communication interface.

The questin is who is checking the return value and whether it is checked
in the right manner.  I looked quickly at the cal site, and it seemed that
the result as stored in a structure field with no checking,  But perhaps
some checking is done afterwards.

julia

>
> Please correct me if I am mistaken.
>
> Thank you.
>
> - Himadri
> ï¿œ
>
>       > -ï¿œ ï¿œ ï¿œ}
>       >
>       >ï¿œ ï¿œ ï¿œ ï¿œspill = PTR_ALIGN(spill, SMP_CACHE_BYTES);
>       >ï¿œ ï¿œ ï¿œ ï¿œphys_addr = virt_to_phys(spill);
>       > --
>       > 2.17.1
>       >
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