Re: [ELISA Safety Architecture WG] [linux-safety] [RFC PATCH 2/2] bust_spinlocks: do not decrement oops_in_progress unconditionally

Hi Gab

I think so, this patch is good.
If you agree to my opinion, please more improve.
In a very rare case, the oops_in_progress could be a negative value.  Because this decrement/increment is a read-modified statement.  On the other hand, shouldn't take exclusions such as spin lock with this function.

if (!oops_in_progress)
change to 
if (oops_in_progress <= 0)

How about?

Best,
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Doctor of Informatics, Specialist
Software Fundamental Technology Group
Application Development Department
Connected & Sharing Solutions Division
AISIN AW CO.,LTD.
YAMAGUCHI Naoto
E-mail： [email protected]
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-----Original Message-----
From: [email protected] <[email protected]> On Behalf Of Paoloni, Gabriele
Sent: Tuesday, October 13, 2020 8:58 PM
To: Paoloni, Gabriele <[email protected]>; [email protected]
Cc: [email protected]
Subject: Re: [ELISA Safety Architecture WG] [linux-safety] [RFC PATCH 2/2] bust_spinlocks: do not decrement oops_in_progress unconditionally

+CC safety arch mailing list

> -----Original Message-----
> From: [email protected] <[email protected]> On 
> Behalf Of Paoloni, Gabriele
> Sent: Tuesday, October 13, 2020 11:50 AM
> To: [email protected]
> Cc: Paoloni, Gabriele <[email protected]>
> Subject: [linux-safety] [RFC PATCH 2/2] bust_spinlocks: do not 
> decrement oops_in_progress unconditionally
> 
> In the current implementation if the input flag is 0 oops_in_progress 
> is unconditionally decremented, thus allowing to become a negative 
> number. Since right now oops_in_progress is a global variable used in 
> the kernel as a conditional flag to check if oops, panic(), BUG() or 
> die() is in progress the current unconditional decrement may lead to 
> unexpected behavior in the Kernel paths conditionally executing over 
> this flag.
> 
> This patch only decrement oops_in_progress if it is non zero
> 
> Signed-off-by: Gabriele Paoloni <[email protected]>
> ---
>  lib/bust_spinlocks.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/lib/bust_spinlocks.c b/lib/bust_spinlocks.c index 
> 594b270161d9..842633ac9130 100644
> --- a/lib/bust_spinlocks.c
> +++ b/lib/bust_spinlocks.c
> @@ -23,6 +23,9 @@
>   * @yes: input flag; if zero decreases oops_in_progress,
>   * otherwise increases it.
>   *
> + * Note: if oops_in_progress is already 0 it will not
> + * be decreased
> + *
>   */
>  void bust_spinlocks(int yes)
>  {
> @@ -33,7 +36,9 @@ void bust_spinlocks(int yes)
>  		unblank_screen();
>  #endif
>  		console_unblank();
> -		if (--oops_in_progress == 0)
> +		if (oops_in_progress)
> +			oops_in_progress--;
> +		if (!oops_in_progress)
>  			wake_up_klogd();
>  	}
>  }
> --
> 2.25.1
> 
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---------------------------------------------------------------------
INTEL CORPORATION ITALIA S.p.A. con unico socio
Sede: Milanofiori Palazzo E 4
CAP 20094 Assago (MI)
Capitale Sociale Euro 104.000,00 interamente versato Partita I.V.A. e Codice Fiscale  04236760155 Repertorio Economico Amministrativo n. 997124 Registro delle Imprese di Milano nr. 183983/5281/33 Soggetta ad attivita' di direzione e coordinamento di INTEL CORPORATION, USA

This e-mail and any attachments may contain confidential material for the sole use of the intended recipient(s). Any review or distribution by others is strictly prohibited. If you are not the intended recipient, please contact the sender and delete all copies.