mbox series

[RFC,0/2] improve bust_spinlocks dependability

Message ID 20201013094938.356837-1-gabriele.paoloni@intel.com (mailing list archive)
Headers show
Series improve bust_spinlocks dependability | expand

Message

Paoloni, Gabriele Oct. 13, 2020, 9:49 a.m. UTC 
This patchset provides a kernel-doc documentation format
for bust_spinlocks() and fixes a weakness where the global
variable oops_in_progress gets unconditionally decremented

Gabriele Paoloni (2):
  bust_spinlocks: add kernel-doc format doc
  bust_spinlocks: do not decrement oops_in_progress unconditionally

 lib/bust_spinlocks.c | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

Comments

Paoloni, Gabriele Oct. 13, 2020, 11:57 a.m. UTC | #1 
+CC safety arch mailing list

> -----Original Message-----
> From: linux-safety@lists.elisa.tech <linux-safety@lists.elisa.tech> On Behalf
> Of Paoloni, Gabriele
> Sent: Tuesday, October 13, 2020 11:50 AM
> To: linux-safety@lists.elisa.tech
> Cc: Paoloni, Gabriele <gabriele.paoloni@intel.com>
> Subject: [linux-safety] [RFC PATCH 1/2] bust_spinlocks: add kernel-doc
> format doc
> 
> In the ELISA Linux Foundation project we are trying to
> improve the functions' documentation to make it more suitable
> to derive functions' specs and write unit tests. This is needed
> to make Linux more usable in functional safety systems.
> So I am adding a proper kernel-doc format for bust_spinlocks.
> 
> Signed-off-by: Gabriele Paoloni <gabriele.paoloni@intel.com>
> ---
> With respect to this patch I have a question on how to set
> the function context; i.e. I don't know if it can be executed
> in any context or if it has limitations.
> ---
>  lib/bust_spinlocks.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/lib/bust_spinlocks.c b/lib/bust_spinlocks.c
> index 8be59f84eaea..594b270161d9 100644
> --- a/lib/bust_spinlocks.c
> +++ b/lib/bust_spinlocks.c
> @@ -5,8 +5,6 @@
>   * Provides a minimal bust_spinlocks for architectures which don't
>   * have one of their own.
>   *
> - * bust_spinlocks() clears any spinlocks which would prevent oops, die(),
> BUG()
> - * and panic() information from reaching the user.
>   */
> 
>  #include <linux/kernel.h>
> @@ -17,6 +15,15 @@
>  #include <linux/vt_kern.h>
>  #include <linux/console.h>
> 
> +/**
> + * bust_spinlocks - increases or decreases oops_in_progress.
> + * if oops_in_progress != 0 spinlocks which would prevent
> + * oops, die(), BUG() and panic() information from reaching
> + * the user are busted.
> + * @yes: input flag; if zero decreases oops_in_progress,
> + * otherwise increases it.
> + *
> + */
>  void bust_spinlocks(int yes)
>  {
>  	if (yes) {
> --
> 2.25.1
> 
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Paoloni, Gabriele Oct. 13, 2020, 11:58 a.m. UTC | #2 
+CC safety arch mailing list

> -----Original Message-----
> From: linux-safety@lists.elisa.tech <linux-safety@lists.elisa.tech> On Behalf
> Of Paoloni, Gabriele
> Sent: Tuesday, October 13, 2020 11:50 AM
> To: linux-safety@lists.elisa.tech
> Cc: Paoloni, Gabriele <gabriele.paoloni@intel.com>
> 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 <gabriele.paoloni@intel.com>
> ---
>  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
> 
> ---------------------------------------------------------------------
> 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
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> 
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> by others is strictly prohibited. If you are not the intended
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> 
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> 

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Partita I.V.A. e Codice Fiscale  04236760155
Repertorio Economico Amministrativo n. 997124 
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I33399_YAMAGUCHI@AISIN-AW.CO.JP Oct. 13, 2020, 1:07 p.m. UTC | #3 
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,
/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/
Doctor of Informatics, Specialist
Software Fundamental Technology Group
Application Development Department
Connected & Sharing Solutions Division
AISIN AW CO.,LTD.
YAMAGUCHI Naoto
E-mail： i33399_YAMAGUCHI@aisin-aw.co.jp
/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/
-----Original Message-----
From: safety-architecture@lists.elisa.tech <safety-architecture@lists.elisa.tech> On Behalf Of Paoloni, Gabriele
Sent: Tuesday, October 13, 2020 8:58 PM
To: Paoloni, Gabriele <gabriele.paoloni@intel.com>; linux-safety@lists.elisa.tech
Cc: safety-architecture@lists.elisa.tech
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: linux-safety@lists.elisa.tech <linux-safety@lists.elisa.tech> On 
> Behalf Of Paoloni, Gabriele
> Sent: Tuesday, October 13, 2020 11:50 AM
> To: linux-safety@lists.elisa.tech
> Cc: Paoloni, Gabriele <gabriele.paoloni@intel.com>
> 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 <gabriele.paoloni@intel.com>
> ---
>  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
> 
> ---------------------------------------------------------------------
> 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.
> 
> 
> 
> 
> 

---------------------------------------------------------------------
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

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Paoloni, Gabriele Oct. 13, 2020, 1:39 p.m. UTC | #4 
> -----Original Message-----
> From: safety-architecture@lists.elisa.tech <safety-
> architecture@lists.elisa.tech> On Behalf Of i33399_yamaguchi@aisin-
> aw.co.jp
> Sent: Tuesday, October 13, 2020 3:07 PM
> To: Paoloni, Gabriele <gabriele.paoloni@intel.com>; linux-
> safety@lists.elisa.tech
> Cc: safety-architecture@lists.elisa.tech
> Subject: 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?

Mmmmm what you are proposing is right, I was just wondering if it is needed....
Looking in the Kernel source code I am seeing that oops_in_progress is always set to 1 or 0
except in https://elixir.bootlin.com/linux/latest/source/kernel/debug/kdb/kdb_io.c#L578.
Here oops_in_progress is incremented and then decremented right after...
actually I am wondering if in this file we should call bust_spinlocks() instead
of directly incrementing/decremeting the variable.... 

Thanks
Gab

> 
> Best,
> /_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/
> Doctor of Informatics, Specialist
> Software Fundamental Technology Group
> Application Development Department
> Connected & Sharing Solutions Division
> AISIN AW CO.,LTD.
> YAMAGUCHI Naoto
> E-mail： i33399_YAMAGUCHI@aisin-aw.co.jp
> /_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/
> -----Original Message-----
> From: safety-architecture@lists.elisa.tech <safety-
> architecture@lists.elisa.tech> On Behalf Of Paoloni, Gabriele
> Sent: Tuesday, October 13, 2020 8:58 PM
> To: Paoloni, Gabriele <gabriele.paoloni@intel.com>; linux-
> safety@lists.elisa.tech
> Cc: safety-architecture@lists.elisa.tech
> 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: linux-safety@lists.elisa.tech <linux-safety@lists.elisa.tech> On
> > Behalf Of Paoloni, Gabriele
> > Sent: Tuesday, October 13, 2020 11:50 AM
> > To: linux-safety@lists.elisa.tech
> > Cc: Paoloni, Gabriele <gabriele.paoloni@intel.com>
> > 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 <gabriele.paoloni@intel.com>
> > ---
> >  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
> >
> > ---------------------------------------------------------------------
> > 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.
> >
> >
> >
> >
> >
> 
> ---------------------------------------------------------------------
> 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
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> This e-mail and any attachments may contain confidential material for the
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> strictly prohibited. If you are not the intended recipient, please contact the
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> 
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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

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Lukas Bulwahn Oct. 14, 2020, 6:04 a.m. UTC | #5 
On Tue, 13 Oct 2020, Paoloni, Gabriele wrote:

> This patchset provides a kernel-doc documentation format
> for bust_spinlocks() and fixes a weakness where the global
> variable oops_in_progress gets unconditionally decremented
> 
> Gabriele Paoloni (2):
>   bust_spinlocks: add kernel-doc format doc
>   bust_spinlocks: do not decrement oops_in_progress unconditionally
> 
>  lib/bust_spinlocks.c | 18 +++++++++++++++---
>  1 file changed, 15 insertions(+), 3 deletions(-)
>

Patchset looks good to me!

I would love to see the feedback you get.

Lukas
 
> -- 
> 2.25.1
> 
> ---------------------------------------------------------------------
> 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.
> 
> 
> 
> 
> 
> 
> 


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