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

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> -----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.