[PATCH] Change wait_for_completion_*_timeout to return a signed long

[PATCH] Change wait_for_completion_*_timeout to return a signed long

[NeilBrown]

wait_for_completion_*_timeout can return:

 0 if the wait timed out
 -ve if the wait was interrupted
 +ve if the completion was completed.

As they currently return an 'unsigned long', the last two cases are not
easily distinguished which can easily result in buggy code, as is the
case for the recently added wait_for_completion_interruptible_timeout
call in net/sunrpc/cache.c

So change them both to return 'long'.  As MAX_SCHEDULE_TIMEOUT is
LONG_MAX, a large +ve return value should never overflow.

Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "J. Bruce Fields" <bfields@fieldses.org>
Signed-off-by: NeilBrown <neilb@suse.de>

diff --git a/include/linux/completion.h b/include/linux/completion.h
index 36d57f7..142fe6f 100644
--- a/include/linux/completion.h
+++ b/include/linux/completion.h
@@ -80,11 +80,11 @@ extern void wait_for_completion(struct completion *);
 extern int wait_for_completion_interruptible(struct completion *x);
 extern int wait_for_completion_killable(struct completion *x);
 extern unsigned long wait_for_completion_timeout(struct completion *x,
 						   unsigned long timeout);
-extern unsigned long wait_for_completion_interruptible_timeout(
-			struct completion *x, unsigned long timeout);
-extern unsigned long wait_for_completion_killable_timeout(
-			struct completion *x, unsigned long timeout);
+extern long wait_for_completion_interruptible_timeout(
+	struct completion *x, unsigned long timeout);
+extern long wait_for_completion_killable_timeout(
+	struct completion *x, unsigned long timeout);
 extern bool try_wait_for_completion(struct completion *x);
 extern bool completion_done(struct completion *x);
 
diff --git a/kernel/sched.c b/kernel/sched.c
index 297d1a0..8f35baf 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -4526,7 +4526,7 @@ EXPORT_SYMBOL(wait_for_completion_interruptible);
  * This waits for either a completion of a specific task to be signaled or for a
  * specified timeout to expire. It is interruptible. The timeout is in jiffies.
  */
-unsigned long __sched
+long __sched
 wait_for_completion_interruptible_timeout(struct completion *x,
 					  unsigned long timeout)
 {
@@ -4559,7 +4559,7 @@ EXPORT_SYMBOL(wait_for_completion_killable);
  * signaled or for a specified timeout to expire. It can be
  * interrupted by a kill signal. The timeout is in jiffies.
  */
-unsigned long __sched
+long __sched
 wait_for_completion_killable_timeout(struct completion *x,
 				     unsigned long timeout)
 {

[tip:sched/core] sched: Change wait_for_completion_*_timeout() to return a signed long

[tip-bot for NeilBrown]

Commit-ID:  6bf4123760a5aece6e4829ce90b70b6ffd751d65
Gitweb:     http://git.kernel.org/tip/6bf4123760a5aece6e4829ce90b70b6ffd751d65
Author:     NeilBrown <neilb@suse.de>
AuthorDate: Wed, 5 Jan 2011 12:50:16 +1100
Committer:  Ingo Molnar <mingo@elte.hu>
CommitDate: Wed, 5 Jan 2011 14:15:50 +0100

sched: Change wait_for_completion_*_timeout() to return a signed long

wait_for_completion_*_timeout() can return:

   0: if the wait timed out
 -ve: if the wait was interrupted
 +ve: if the completion was completed.

As they currently return an 'unsigned long', the last two cases
are not easily distinguished which can easily result in buggy
code, as is the case for the recently added
wait_for_completion_interruptible_timeout() call in
net/sunrpc/cache.c

So change them both to return 'long'.  As MAX_SCHEDULE_TIMEOUT
is LONG_MAX, a large +ve return value should never overflow.

Signed-off-by: NeilBrown <neilb@suse.de>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: J.  Bruce Fields <bfields@fieldses.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
LKML-Reference: <20110105125016.64ccab0e@notabene.brown>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
 include/linux/completion.h |    8 ++++----
 kernel/sched.c             |    4 ++--
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/include/linux/completion.h b/include/linux/completion.h
index 36d57f7..51494e6 100644
--- a/include/linux/completion.h
+++ b/include/linux/completion.h
@@ -81,10 +81,10 @@ extern int wait_for_completion_interruptible(struct completion *x);
 extern int wait_for_completion_killable(struct completion *x);
 extern unsigned long wait_for_completion_timeout(struct completion *x,
 						   unsigned long timeout);
-extern unsigned long wait_for_completion_interruptible_timeout(
-			struct completion *x, unsigned long timeout);
-extern unsigned long wait_for_completion_killable_timeout(
-			struct completion *x, unsigned long timeout);
+extern long wait_for_completion_interruptible_timeout(
+	struct completion *x, unsigned long timeout);
+extern long wait_for_completion_killable_timeout(
+	struct completion *x, unsigned long timeout);
 extern bool try_wait_for_completion(struct completion *x);
 extern bool completion_done(struct completion *x);
 
diff --git a/kernel/sched.c b/kernel/sched.c
index f2f914e..114a0de 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -4395,7 +4395,7 @@ EXPORT_SYMBOL(wait_for_completion_interruptible);
  * This waits for either a completion of a specific task to be signaled or for a
  * specified timeout to expire. It is interruptible. The timeout is in jiffies.
  */
-unsigned long __sched
+long __sched
 wait_for_completion_interruptible_timeout(struct completion *x,
 					  unsigned long timeout)
 {
@@ -4428,7 +4428,7 @@ EXPORT_SYMBOL(wait_for_completion_killable);
  * signaled or for a specified timeout to expire. It can be
  * interrupted by a kill signal. The timeout is in jiffies.
  */
-unsigned long __sched
+long __sched
 wait_for_completion_killable_timeout(struct completion *x,
 				     unsigned long timeout)
 {

Re: [PATCH] Change wait_for_completion_*_timeout to return a signed long

[Andrew Morton]

On Wed, 5 Jan 2011 12:50:16 +1100
NeilBrown <neilb@suse.de> wrote:

> 
> wait_for_completion_*_timeout can return:
> 
>  0 if the wait timed out
>  -ve if the wait was interrupted
>  +ve if the completion was completed.
> 
> As they currently return an 'unsigned long', the last two cases are not
> easily distinguished which can easily result in buggy code, as is the
> case for the recently added wait_for_completion_interruptible_timeout
> call in net/sunrpc/cache.c
> 
> So change them both to return 'long'.  As MAX_SCHEDULE_TIMEOUT is
> LONG_MAX, a large +ve return value should never overflow.
> 
> ...
>
> --- a/include/linux/completion.h
> +++ b/include/linux/completion.h
> @@ -80,11 +80,11 @@ extern void wait_for_completion(struct completion *);
>  extern int wait_for_completion_interruptible(struct completion *x);
>  extern int wait_for_completion_killable(struct completion *x);
>  extern unsigned long wait_for_completion_timeout(struct completion *x,
>  						   unsigned long timeout);
> -extern unsigned long wait_for_completion_interruptible_timeout(
> -			struct completion *x, unsigned long timeout);
> -extern unsigned long wait_for_completion_killable_timeout(
> -			struct completion *x, unsigned long timeout);
> +extern long wait_for_completion_interruptible_timeout(
> +	struct completion *x, unsigned long timeout);
> +extern long wait_for_completion_killable_timeout(
> +	struct completion *x, unsigned long timeout);
>  extern bool try_wait_for_completion(struct completion *x);
>  extern bool completion_done(struct completion *x);
>  

That's a half-patch, isn't it?  wait_for_completion_interruptible()
still incorrectly returns `int' and wait_for_completion_timeout() still
returns `unsigned long'.

Re: [PATCH] Change wait_for_completion_*_timeout to return a signed long

[NeilBrown]

On Wed, 5 Jan 2011 14:57:25 -0800 Andrew Morton <akpm@linux-foundation.org>
wrote:

> On Wed, 5 Jan 2011 12:50:16 +1100
> NeilBrown <neilb@suse.de> wrote:
> 
> > 
> > wait_for_completion_*_timeout can return:
> > 
> >  0 if the wait timed out
> >  -ve if the wait was interrupted
> >  +ve if the completion was completed.
> > 
> > As they currently return an 'unsigned long', the last two cases are not
> > easily distinguished which can easily result in buggy code, as is the
> > case for the recently added wait_for_completion_interruptible_timeout
> > call in net/sunrpc/cache.c
> > 
> > So change them both to return 'long'.  As MAX_SCHEDULE_TIMEOUT is
> > LONG_MAX, a large +ve return value should never overflow.
> > 
> > ...
> >
> > --- a/include/linux/completion.h
> > +++ b/include/linux/completion.h
> > @@ -80,11 +80,11 @@ extern void wait_for_completion(struct completion *);
> >  extern int wait_for_completion_interruptible(struct completion *x);
> >  extern int wait_for_completion_killable(struct completion *x);
> >  extern unsigned long wait_for_completion_timeout(struct completion *x,
> >  						   unsigned long timeout);
> > -extern unsigned long wait_for_completion_interruptible_timeout(
> > -			struct completion *x, unsigned long timeout);
> > -extern unsigned long wait_for_completion_killable_timeout(
> > -			struct completion *x, unsigned long timeout);
> > +extern long wait_for_completion_interruptible_timeout(
> > +	struct completion *x, unsigned long timeout);
> > +extern long wait_for_completion_killable_timeout(
> > +	struct completion *x, unsigned long timeout);
> >  extern bool try_wait_for_completion(struct completion *x);
> >  extern bool completion_done(struct completion *x);
> >  
> 
> That's a half-patch, isn't it?  wait_for_completion_interruptible()
> still incorrectly returns `int' and wait_for_completion_timeout() still
> returns `unsigned long'.

Half a patch is better than half a bug report is better than half an oops
message is better than none ..... (am I showing my age?)


wait_for_completion_interruptile returns either a negative error (-ERESTART)
or 0.  So 'int' is fine.  Ditto for wait_for_completion_killable.
wait_for_completion_timeout returns a positive timeout-remaining or 0, so
'unsigned long' is fine.

It is only when we come to combining 'interruptible' and 'timeout' that we
need signed and long.

Now maybe it would be good to use "signed long" for all of them because
consistency is a nice thing.  Or maybe it is best to specify in each case the
return type that is most clearly meaningful because that communicates more
clearly.
I really cannot say - I just wanted to fix a bug :-)

NeilBrown

Re: [tip:sched/core] sched: Change wait_for_completion_*_timeout() to return a signed long

[J. Bruce Fields]

Doesn't this belong in 2.6.37.y as well?

--b.

On Wed, Jan 05, 2011 at 02:07:12PM +0000, tip-bot for NeilBrown wrote:
> Commit-ID:  6bf4123760a5aece6e4829ce90b70b6ffd751d65
> Gitweb:     http://git.kernel.org/tip/6bf4123760a5aece6e4829ce90b70b6ffd751d65
> Author:     NeilBrown <neilb@suse.de>
> AuthorDate: Wed, 5 Jan 2011 12:50:16 +1100
> Committer:  Ingo Molnar <mingo@elte.hu>
> CommitDate: Wed, 5 Jan 2011 14:15:50 +0100
> 
> sched: Change wait_for_completion_*_timeout() to return a signed long
> 
> wait_for_completion_*_timeout() can return:
> 
>    0: if the wait timed out
>  -ve: if the wait was interrupted
>  +ve: if the completion was completed.
> 
> As they currently return an 'unsigned long', the last two cases
> are not easily distinguished which can easily result in buggy
> code, as is the case for the recently added
> wait_for_completion_interruptible_timeout() call in
> net/sunrpc/cache.c
> 
> So change them both to return 'long'.  As MAX_SCHEDULE_TIMEOUT
> is LONG_MAX, a large +ve return value should never overflow.
> 
> Signed-off-by: NeilBrown <neilb@suse.de>
> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
> Cc: J.  Bruce Fields <bfields@fieldses.org>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Linus Torvalds <torvalds@linux-foundation.org>
> LKML-Reference: <20110105125016.64ccab0e@notabene.brown>
> Signed-off-by: Ingo Molnar <mingo@elte.hu>
> ---
>  include/linux/completion.h |    8 ++++----
>  kernel/sched.c             |    4 ++--
>  2 files changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/include/linux/completion.h b/include/linux/completion.h
> index 36d57f7..51494e6 100644
> --- a/include/linux/completion.h
> +++ b/include/linux/completion.h
> @@ -81,10 +81,10 @@ extern int wait_for_completion_interruptible(struct completion *x);
>  extern int wait_for_completion_killable(struct completion *x);
>  extern unsigned long wait_for_completion_timeout(struct completion *x,
>  						   unsigned long timeout);
> -extern unsigned long wait_for_completion_interruptible_timeout(
> -			struct completion *x, unsigned long timeout);
> -extern unsigned long wait_for_completion_killable_timeout(
> -			struct completion *x, unsigned long timeout);
> +extern long wait_for_completion_interruptible_timeout(
> +	struct completion *x, unsigned long timeout);
> +extern long wait_for_completion_killable_timeout(
> +	struct completion *x, unsigned long timeout);
>  extern bool try_wait_for_completion(struct completion *x);
>  extern bool completion_done(struct completion *x);
>  
> diff --git a/kernel/sched.c b/kernel/sched.c
> index f2f914e..114a0de 100644
> --- a/kernel/sched.c
> +++ b/kernel/sched.c
> @@ -4395,7 +4395,7 @@ EXPORT_SYMBOL(wait_for_completion_interruptible);
>   * This waits for either a completion of a specific task to be signaled or for a
>   * specified timeout to expire. It is interruptible. The timeout is in jiffies.
>   */
> -unsigned long __sched
> +long __sched
>  wait_for_completion_interruptible_timeout(struct completion *x,
>  					  unsigned long timeout)
>  {
> @@ -4428,7 +4428,7 @@ EXPORT_SYMBOL(wait_for_completion_killable);
>   * signaled or for a specified timeout to expire. It can be
>   * interrupted by a kill signal. The timeout is in jiffies.
>   */
> -unsigned long __sched
> +long __sched
>  wait_for_completion_killable_timeout(struct completion *x,
>  				     unsigned long timeout)
>  {

Re: [tip:sched/core] sched: Change wait_for_completion_*_timeout() to return a signed long

[NeilBrown]

On Tue, 11 Jan 2011 16:44:58 -0500 "J. Bruce Fields" <bfields@fieldses.org>
wrote:

> Doesn't this belong in 2.6.37.y as well?

Yes indeed!
I should have tagged it for Cc:stable@kernel.org in the first place.  I had
been meaning to forward it to stable@kernel.org, but you beat me to it!

Thanks,
NeilBrown


> 
> --b.
> 
> On Wed, Jan 05, 2011 at 02:07:12PM +0000, tip-bot for NeilBrown wrote:
> > Commit-ID:  6bf4123760a5aece6e4829ce90b70b6ffd751d65
> > Gitweb:     http://git.kernel.org/tip/6bf4123760a5aece6e4829ce90b70b6ffd751d65
> > Author:     NeilBrown <neilb@suse.de>
> > AuthorDate: Wed, 5 Jan 2011 12:50:16 +1100
> > Committer:  Ingo Molnar <mingo@elte.hu>
> > CommitDate: Wed, 5 Jan 2011 14:15:50 +0100
> > 
> > sched: Change wait_for_completion_*_timeout() to return a signed long
> > 
> > wait_for_completion_*_timeout() can return:
> > 
> >    0: if the wait timed out
> >  -ve: if the wait was interrupted
> >  +ve: if the completion was completed.
> > 
> > As they currently return an 'unsigned long', the last two cases
> > are not easily distinguished which can easily result in buggy
> > code, as is the case for the recently added
> > wait_for_completion_interruptible_timeout() call in
> > net/sunrpc/cache.c
> > 
> > So change them both to return 'long'.  As MAX_SCHEDULE_TIMEOUT
> > is LONG_MAX, a large +ve return value should never overflow.
> > 
> > Signed-off-by: NeilBrown <neilb@suse.de>
> > Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
> > Cc: J.  Bruce Fields <bfields@fieldses.org>
> > Cc: Andrew Morton <akpm@linux-foundation.org>
> > Cc: Linus Torvalds <torvalds@linux-foundation.org>
> > LKML-Reference: <20110105125016.64ccab0e@notabene.brown>
> > Signed-off-by: Ingo Molnar <mingo@elte.hu>
> > ---
> >  include/linux/completion.h |    8 ++++----
> >  kernel/sched.c             |    4 ++--
> >  2 files changed, 6 insertions(+), 6 deletions(-)
> > 
> > diff --git a/include/linux/completion.h b/include/linux/completion.h
> > index 36d57f7..51494e6 100644
> > --- a/include/linux/completion.h
> > +++ b/include/linux/completion.h
> > @@ -81,10 +81,10 @@ extern int wait_for_completion_interruptible(struct completion *x);
> >  extern int wait_for_completion_killable(struct completion *x);
> >  extern unsigned long wait_for_completion_timeout(struct completion *x,
> >  						   unsigned long timeout);
> > -extern unsigned long wait_for_completion_interruptible_timeout(
> > -			struct completion *x, unsigned long timeout);
> > -extern unsigned long wait_for_completion_killable_timeout(
> > -			struct completion *x, unsigned long timeout);
> > +extern long wait_for_completion_interruptible_timeout(
> > +	struct completion *x, unsigned long timeout);
> > +extern long wait_for_completion_killable_timeout(
> > +	struct completion *x, unsigned long timeout);
> >  extern bool try_wait_for_completion(struct completion *x);
> >  extern bool completion_done(struct completion *x);
> >  
> > diff --git a/kernel/sched.c b/kernel/sched.c
> > index f2f914e..114a0de 100644
> > --- a/kernel/sched.c
> > +++ b/kernel/sched.c
> > @@ -4395,7 +4395,7 @@ EXPORT_SYMBOL(wait_for_completion_interruptible);
> >   * This waits for either a completion of a specific task to be signaled or for a
> >   * specified timeout to expire. It is interruptible. The timeout is in jiffies.
> >   */
> > -unsigned long __sched
> > +long __sched
> >  wait_for_completion_interruptible_timeout(struct completion *x,
> >  					  unsigned long timeout)
> >  {
> > @@ -4428,7 +4428,7 @@ EXPORT_SYMBOL(wait_for_completion_killable);
> >   * signaled or for a specified timeout to expire. It can be
> >   * interrupted by a kill signal. The timeout is in jiffies.
> >   */
> > -unsigned long __sched
> > +long __sched
> >  wait_for_completion_killable_timeout(struct completion *x,
> >  				     unsigned long timeout)
> >  {

Re: [stable] [tip:sched/core] sched: Change wait_for_completion_*_timeout() to return a signed long

[Greg KH]

On Wed, Jan 12, 2011 at 09:07:07AM +1100, NeilBrown wrote:
> On Tue, 11 Jan 2011 16:44:58 -0500 "J. Bruce Fields" <bfields@fieldses.org>
> wrote:
> 
> > Doesn't this belong in 2.6.37.y as well?
> 
> Yes indeed!
> I should have tagged it for Cc:stable@kernel.org in the first place.  I had
> been meaning to forward it to stable@kernel.org, but you beat me to it!

Now applied, thanks.

greg k-h