[1/3] cleanup: add conditional guard helper

Commit Message

David Lechner Oct. 1, 2024, 10:30 p.m. UTC

Add a new if_not_cond_guard() macro to cleanup.h for handling
conditional guards such as mutext_trylock().

This is more ergonomic than scoped_cond_guard() for most use cases.
Instead of hiding the error handling statement in the macro args, it
works like a normal if statement and allow the error path to be indented
while the normal code flow path is not indented. And it avoid unwanted
side-effect from hidden for loop in scoped_cond_guard().

Signed-off-by: David Lechner <[e-mail]>
---
 include/linux/cleanup.h | 11 +++++++++++
 1 file changed, 11 insertions(+)

Comments

Dan Williams Oct. 4, 2024, 5:34 p.m. UTC | #1

[ add Fabio ]

David Lechner wrote:
> Add a new if_not_cond_guard() macro to cleanup.h for handling
> conditional guards such as mutext_trylock().
> 
> This is more ergonomic than scoped_cond_guard() for most use cases.
> Instead of hiding the error handling statement in the macro args, it
> works like a normal if statement and allow the error path to be indented
> while the normal code flow path is not indented. And it avoid unwanted
> side-effect from hidden for loop in scoped_cond_guard().
> 
> Signed-off-by: David Lechner <[e-mail]>

Hi David,

When you update this to the if_not_guard() name can you also add Fabio as a
co-developer? His work [1] contributed to eliciting the response from Linus,
and then this patch takes the novel additional step to create an "if ()" macro.

Thanks for pushing this forward!

[1]: http://lore.kernel.org/[e-mail]

David Lechner Oct. 4, 2024, 8:27 p.m. UTC | #2

On 10/4/24 12:34 PM, Dan Williams wrote:
> [ add Fabio ]
> 
> David Lechner wrote:
>> Add a new if_not_cond_guard() macro to cleanup.h for handling
>> conditional guards such as mutext_trylock().
>>
>> This is more ergonomic than scoped_cond_guard() for most use cases.
>> Instead of hiding the error handling statement in the macro args, it
>> works like a normal if statement and allow the error path to be indented
>> while the normal code flow path is not indented. And it avoid unwanted
>> side-effect from hidden for loop in scoped_cond_guard().
>>
>> Signed-off-by: David Lechner <[e-mail]>
> 
> Hi David,
> 
> When you update this to the if_not_guard() name can you also add Fabio as a
> co-developer? His work [1] contributed to eliciting the response from Linus,
> and then this patch takes the novel additional step to create an "if ()" macro.
> 
> Thanks for pushing this forward!
> 
> [1]: http://lore.kernel.org/[e-mail]

Sure, I didn't dig deep enough to find that patch, but basically
the same idea. :-)

Peter Zijlstra Oct. 18, 2024, 11:15 a.m. UTC | #3

On Tue, Oct 01, 2024 at 05:30:18PM -0500, David Lechner wrote:
> Add a new if_not_cond_guard() macro to cleanup.h for handling
> conditional guards such as mutext_trylock().
> 
> This is more ergonomic than scoped_cond_guard() for most use cases.
> Instead of hiding the error handling statement in the macro args, it
> works like a normal if statement and allow the error path to be indented
> while the normal code flow path is not indented. And it avoid unwanted
> side-effect from hidden for loop in scoped_cond_guard().
> 
> Signed-off-by: David Lechner <[e-mail]>
> ---
>  include/linux/cleanup.h | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/include/linux/cleanup.h b/include/linux/cleanup.h
> index 038b2d523bf8..682bb3fadfc9 100644
> --- a/include/linux/cleanup.h
> +++ b/include/linux/cleanup.h
> @@ -273,6 +273,10 @@ static inline class_##_name##_t class_##_name##ext##_constructor(_init_args) \
>   *	an anonymous instance of the (guard) class, not recommended for
>   *	conditional locks.
>   *
> + * if_not_cond_guard(name, args...) { <error handling> }:
> + *	convenience macro for conditional guards that calls the statement that
> + *	follows only if the lock was not acquired (typically an error return).
> + *
>   * scoped_guard (name, args...) { }:
>   *	similar to CLASS(name, scope)(args), except the variable (with the
>   *	explicit name 'scope') is declard in a for-loop such that its scope is
> @@ -304,6 +308,13 @@ static inline class_##_name##_t class_##_name##ext##_constructor(_init_args) \
>  
>  #define __guard_ptr(_name) class_##_name##_lock_ptr
>  
> +#define __if_not_cond_guard(_name, _id, args...)	\
> +	CLASS(_name, _id)(args);			\
> +	if (!__guard_ptr(_name)(&_id))
> +
> +#define if_not_cond_guard(_name, args...) \
> +	__if_not_cond_guard(_name, __UNIQUE_ID(guard), args)
> +
>  #define scoped_guard(_name, args...)					\
>  	for (CLASS(_name, scope)(args),					\
>  	     *done = NULL; __guard_ptr(_name)(&scope) && !done; done = (void *)1)


So if I stick this on top of:

  https://lkml.kernel.org/r/[e-mail]

then I can add the below:

--- a/include/linux/cleanup.h
+++ b/include/linux/cleanup.h
@@ -277,6 +277,8 @@ static inline class_##_name##_t class_##
  *	convenience macro for conditional guards that calls the statement that
  *	follows only if the lock was not acquired (typically an error return).
  *
+ *	Only for conditional locks.
+ *
  * scoped_guard (name, args...) { }:
  *	similar to CLASS(name, scope)(args), except the variable (with the
  *	explicit name 'scope') is declard in a for-loop such that its scope is
@@ -290,7 +292,6 @@ static inline class_##_name##_t class_##
  *      acquire fails.
  *
  *	Only for conditional locks.
- *
  */
 
 #define __DEFINE_CLASS_IS_CONDITIONAL(_name, _is_cond)	\
@@ -342,6 +343,7 @@ _label:										\
 		       __UNIQUE_ID(label), args)
 
 #define __if_not_guard(_name, _id, args...)		\
+	BUILD_BUG_ON(!__is_cond_ptr(_name));		\
 	CLASS(_name, _id)(args);			\
 	if (!__guard_ptr(_name)(&_id))
 

That make sense to people?

I've queued these two patches:

  git://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git locking/core

But lacking if_not_guard() users, the robot isn't really going to give
me much feedback there, I suppose...

Przemek Kitszel Oct. 18, 2024, 12:31 p.m. UTC | #4

On 10/18/24 13:15, Peter Zijlstra wrote:
> On Tue, Oct 01, 2024 at 05:30:18PM -0500, David Lechner wrote:
>> Add a new if_not_cond_guard() macro to cleanup.h for handling
>> conditional guards such as mutext_trylock().
>>
>> This is more ergonomic than scoped_cond_guard() for most use cases.
>> Instead of hiding the error handling statement in the macro args, it
>> works like a normal if statement and allow the error path to be indented
>> while the normal code flow path is not indented. And it avoid unwanted
>> side-effect from hidden for loop in scoped_cond_guard().
>>
>> Signed-off-by: David Lechner <[e-mail]>

So this is guard()() with error handler for cond class of locks.
I would name such guard_or_err(), or guard_or_err_block(), to make it
obvious why there is a block attached (so bad we could not ENFORCE that
there is a block atached).

Then, having it, it would make sense to not only limit guard_or_err() to
cond class of locks, but also forbid plain guard() with cond locks
(instead just discouraging it in the doc).

>> ---
>>   include/linux/cleanup.h | 11 +++++++++++
>>   1 file changed, 11 insertions(+)
>>
>> diff --git a/include/linux/cleanup.h b/include/linux/cleanup.h
>> index 038b2d523bf8..682bb3fadfc9 100644
>> --- a/include/linux/cleanup.h
>> +++ b/include/linux/cleanup.h
>> @@ -273,6 +273,10 @@ static inline class_##_name##_t class_##_name##ext##_constructor(_init_args) \
>>    *	an anonymous instance of the (guard) class, not recommended for
>>    *	conditional locks.
>>    *
>> + * if_not_cond_guard(name, args...) { <error handling> }:
>> + *	convenience macro for conditional guards that calls the statement that
>> + *	follows only if the lock was not acquired (typically an error return).
>> + *
>>    * scoped_guard (name, args...) { }:
>>    *	similar to CLASS(name, scope)(args), except the variable (with the
>>    *	explicit name 'scope') is declard in a for-loop such that its scope is
>> @@ -304,6 +308,13 @@ static inline class_##_name##_t class_##_name##ext##_constructor(_init_args) \
>>   
>>   #define __guard_ptr(_name) class_##_name##_lock_ptr
>>   
>> +#define __if_not_cond_guard(_name, _id, args...)	\
>> +	CLASS(_name, _id)(args);			\
>> +	if (!__guard_ptr(_name)(&_id))
>> +
>> +#define if_not_cond_guard(_name, args...) \
>> +	__if_not_cond_guard(_name, __UNIQUE_ID(guard), args)
>> +
>>   #define scoped_guard(_name, args...)					\
>>   	for (CLASS(_name, scope)(args),					\
>>   	     *done = NULL; __guard_ptr(_name)(&scope) && !done; done = (void *)1)
> 
> 
> So if I stick this on top of:
> 
>    https://lkml.kernel.org/r/[e-mail]

I have v4 that fixes non-cond version. Apologies it took me that long.
[v4] 
https://lore.kernel.org/netdev/[e-mail]

I have tested it also with the unrechable() calls removed, as suggested
by David Lechner here:
https://lore.kernel.org/netdev/[e-mail]

> 
> then I can add the below:
> 
> --- a/include/linux/cleanup.h
> +++ b/include/linux/cleanup.h
> @@ -277,6 +277,8 @@ static inline class_##_name##_t class_##
>    *	convenience macro for conditional guards that calls the statement that
>    *	follows only if the lock was not acquired (typically an error return).
>    *
> + *	Only for conditional locks.
> + *
>    * scoped_guard (name, args...) { }:
>    *	similar to CLASS(name, scope)(args), except the variable (with the
>    *	explicit name 'scope') is declard in a for-loop such that its scope is
> @@ -290,7 +292,6 @@ static inline class_##_name##_t class_##
>    *      acquire fails.
>    *
>    *	Only for conditional locks.
> - *
>    */
>   
>   #define __DEFINE_CLASS_IS_CONDITIONAL(_name, _is_cond)	\
> @@ -342,6 +343,7 @@ _label:										\
>   		       __UNIQUE_ID(label), args)
>   
>   #define __if_not_guard(_name, _id, args...)		\
> +	BUILD_BUG_ON(!__is_cond_ptr(_name));		\
>   	CLASS(_name, _id)(args);			\
>   	if (!__guard_ptr(_name)(&_id))
>   
> 
> That make sense to people?

despite name, looks promising!

> 
> I've queued these two patches:
> 
>    git://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git locking/core
> 
> But lacking if_not_guard() users, the robot isn't really going to give
> me much feedback there, I suppose...

Couldn't you just pick the other patches, that use the newly introduced
macro?

Jonathan Cameron Oct. 18, 2024, 4:29 p.m. UTC | #5

On Fri, 18 Oct 2024 14:31:43 +0200
Przemek Kitszel <[e-mail]> wrote:

> On 10/18/24 13:15, Peter Zijlstra wrote:
> > On Tue, Oct 01, 2024 at 05:30:18PM -0500, David Lechner wrote:  
> >> Add a new if_not_cond_guard() macro to cleanup.h for handling
> >> conditional guards such as mutext_trylock().
> >>
> >> This is more ergonomic than scoped_cond_guard() for most use cases.
> >> Instead of hiding the error handling statement in the macro args, it
> >> works like a normal if statement and allow the error path to be indented
> >> while the normal code flow path is not indented. And it avoid unwanted
> >> side-effect from hidden for loop in scoped_cond_guard().
> >>
> >> Signed-off-by: David Lechner <[e-mail]>  
> 
> So this is guard()() with error handler for cond class of locks.
> I would name such guard_or_err(), or guard_or_err_block(), to make it
> obvious why there is a block attached (so bad we could not ENFORCE that
> there is a block atached).
> 
> Then, having it, it would make sense to not only limit guard_or_err() to
> cond class of locks, but also forbid plain guard() with cond locks
> (instead just discouraging it in the doc).
> 
> >> ---
> >>   include/linux/cleanup.h | 11 +++++++++++
> >>   1 file changed, 11 insertions(+)
> >>
> >> diff --git a/include/linux/cleanup.h b/include/linux/cleanup.h
> >> index 038b2d523bf8..682bb3fadfc9 100644
> >> --- a/include/linux/cleanup.h
> >> +++ b/include/linux/cleanup.h
> >> @@ -273,6 +273,10 @@ static inline class_##_name##_t class_##_name##ext##_constructor(_init_args) \
> >>    *	an anonymous instance of the (guard) class, not recommended for
> >>    *	conditional locks.
> >>    *
> >> + * if_not_cond_guard(name, args...) { <error handling> }:
> >> + *	convenience macro for conditional guards that calls the statement that
> >> + *	follows only if the lock was not acquired (typically an error return).
> >> + *
> >>    * scoped_guard (name, args...) { }:
> >>    *	similar to CLASS(name, scope)(args), except the variable (with the
> >>    *	explicit name 'scope') is declard in a for-loop such that its scope is
> >> @@ -304,6 +308,13 @@ static inline class_##_name##_t class_##_name##ext##_constructor(_init_args) \
> >>   
> >>   #define __guard_ptr(_name) class_##_name##_lock_ptr
> >>   
> >> +#define __if_not_cond_guard(_name, _id, args...)	\
> >> +	CLASS(_name, _id)(args);			\
> >> +	if (!__guard_ptr(_name)(&_id))
> >> +
> >> +#define if_not_cond_guard(_name, args...) \
> >> +	__if_not_cond_guard(_name, __UNIQUE_ID(guard), args)
> >> +
> >>   #define scoped_guard(_name, args...)					\
> >>   	for (CLASS(_name, scope)(args),					\
> >>   	     *done = NULL; __guard_ptr(_name)(&scope) && !done; done = (void *)1)  
> > 
> > 
> > So if I stick this on top of:
> > 
> >    https://lkml.kernel.org/r/[e-mail]  
> 
> I have v4 that fixes non-cond version. Apologies it took me that long.
> [v4] 
> https://lore.kernel.org/netdev/[e-mail]
> 
> I have tested it also with the unrechable() calls removed, as suggested
> by David Lechner here:
> https://lore.kernel.org/netdev/[e-mail]
> 
> > 
> > then I can add the below:
> > 
> > --- a/include/linux/cleanup.h
> > +++ b/include/linux/cleanup.h
> > @@ -277,6 +277,8 @@ static inline class_##_name##_t class_##
> >    *	convenience macro for conditional guards that calls the statement that
> >    *	follows only if the lock was not acquired (typically an error return).
> >    *
> > + *	Only for conditional locks.
> > + *
> >    * scoped_guard (name, args...) { }:
> >    *	similar to CLASS(name, scope)(args), except the variable (with the
> >    *	explicit name 'scope') is declard in a for-loop such that its scope is
> > @@ -290,7 +292,6 @@ static inline class_##_name##_t class_##
> >    *      acquire fails.
> >    *
> >    *	Only for conditional locks.
> > - *
> >    */
> >   
> >   #define __DEFINE_CLASS_IS_CONDITIONAL(_name, _is_cond)	\
> > @@ -342,6 +343,7 @@ _label:										\
> >   		       __UNIQUE_ID(label), args)
> >   
> >   #define __if_not_guard(_name, _id, args...)		\
> > +	BUILD_BUG_ON(!__is_cond_ptr(_name));		\
> >   	CLASS(_name, _id)(args);			\
> >   	if (!__guard_ptr(_name)(&_id))
> >   
> > 
> > That make sense to people?  
> 
> despite name, looks promising!
> 
> > 
> > I've queued these two patches:
> > 
> >    git://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git locking/core
> > 
> > But lacking if_not_guard() users, the robot isn't really going to give
> > me much feedback there, I suppose...  
> 
> Couldn't you just pick the other patches, that use the newly introduced
> macro?

For a test, sure, but there is a lot of ad7380 work in flight and I'd rather
not push that back a cycle for this improvement (nice though it is!)

If it looks good, an immutable branch would be great, or I could just merge
from Peter's tree if that is stable.

Similarly there is a high risk of the CXL code changing for other reasons
this cycle, but same solution would work.

Jonathan




> 
> 
>

Dan Williams Oct. 18, 2024, 7:29 p.m. UTC | #6

Peter Zijlstra wrote:
> On Tue, Oct 01, 2024 at 05:30:18PM -0500, David Lechner wrote:
> > Add a new if_not_cond_guard() macro to cleanup.h for handling
> > conditional guards such as mutext_trylock().
> > 
> > This is more ergonomic than scoped_cond_guard() for most use cases.
> > Instead of hiding the error handling statement in the macro args, it
> > works like a normal if statement and allow the error path to be indented
> > while the normal code flow path is not indented. And it avoid unwanted
> > side-effect from hidden for loop in scoped_cond_guard().
> > 
> > Signed-off-by: David Lechner <[e-mail]>
> > ---
> >  include/linux/cleanup.h | 11 +++++++++++
> >  1 file changed, 11 insertions(+)
> > 
[..]
> I've queued these two patches:
> 
>   git://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git locking/core
> 
> But lacking if_not_guard() users, the robot isn't really going to give
> me much feedback there, I suppose...

Looks good. If that branch is rebase-able it would be nice to add some
credit tags to "cleanup: Add conditional guard helper":

Co-developed-by: Fabio M. De Francesco <[e-mail]>
Signed-off-by: Fabio M. De Francesco <[e-mail]>

David and I talked about that here:

http://lore.kernel.org/[e-mail]

Also feel free to add:

Reviewed-by: Dan Williams <[e-mail]>

Thanks, Peter!

Peter Zijlstra Oct. 23, 2024, 10:57 a.m. UTC | #7

On Fri, Oct 18, 2024 at 12:29:27PM -0700, Dan Williams wrote:
> Peter Zijlstra wrote:
> > On Tue, Oct 01, 2024 at 05:30:18PM -0500, David Lechner wrote:
> > > Add a new if_not_cond_guard() macro to cleanup.h for handling
> > > conditional guards such as mutext_trylock().
> > > 
> > > This is more ergonomic than scoped_cond_guard() for most use cases.
> > > Instead of hiding the error handling statement in the macro args, it
> > > works like a normal if statement and allow the error path to be indented
> > > while the normal code flow path is not indented. And it avoid unwanted
> > > side-effect from hidden for loop in scoped_cond_guard().
> > > 
> > > Signed-off-by: David Lechner <[e-mail]>
> > > ---
> > >  include/linux/cleanup.h | 11 +++++++++++
> > >  1 file changed, 11 insertions(+)
> > > 
> [..]
> > I've queued these two patches:
> > 
> >   git://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git locking/core
> > 
> > But lacking if_not_guard() users, the robot isn't really going to give
> > me much feedback there, I suppose...
> 
> Looks good. If that branch is rebase-able it would be nice to add some
> credit tags to "cleanup: Add conditional guard helper":
> 
> Co-developed-by: Fabio M. De Francesco <[e-mail]>
> Signed-off-by: Fabio M. De Francesco <[e-mail]>
> 
> David and I talked about that here:
> 
> http://lore.kernel.org/[e-mail]
> 
> Also feel free to add:
> 
> Reviewed-by: Dan Williams <[e-mail]>

I rebased because I had to magic in the v4 from Przemek, and I added the
above tags to the if_not_guard() thing.

I've also pushed out a locking/test branch that includes the iio
conversion for the robots.

Once I push to tip/locking/core (people will get robot mail) the commits
should be stable and can be used in other branches if so desired.

Patch

diff --git a/include/linux/cleanup.h b/include/linux/cleanup.h
index 038b2d523bf8..682bb3fadfc9 100644
--- a/include/linux/cleanup.h
+++ b/include/linux/cleanup.h
@@ -273,6 +273,10 @@  static inline class_##_name##_t class_##_name##ext##_constructor(_init_args) \
  *	an anonymous instance of the (guard) class, not recommended for
  *	conditional locks.
  *
+ * if_not_cond_guard(name, args...) { <error handling> }:
+ *	convenience macro for conditional guards that calls the statement that
+ *	follows only if the lock was not acquired (typically an error return).
+ *
  * scoped_guard (name, args...) { }:
  *	similar to CLASS(name, scope)(args), except the variable (with the
  *	explicit name 'scope') is declard in a for-loop such that its scope is
@@ -304,6 +308,13 @@  static inline class_##_name##_t class_##_name##ext##_constructor(_init_args) \
 
 #define __guard_ptr(_name) class_##_name##_lock_ptr
 
+#define __if_not_cond_guard(_name, _id, args...)	\
+	CLASS(_name, _id)(args);			\
+	if (!__guard_ptr(_name)(&_id))
+
+#define if_not_cond_guard(_name, args...) \
+	__if_not_cond_guard(_name, __UNIQUE_ID(guard), args)
+
 #define scoped_guard(_name, args...)					\
 	for (CLASS(_name, scope)(args),					\
 	     *done = NULL; __guard_ptr(_name)(&scope) && !done; done = (void *)1)