Re: [PATCH v2 1/2] fs: add asserting functions for sb_start_{write,pagefault,intwrite}

[Dave Chinner <david@fromorbit.com>]

On Tue, Feb 15, 2022 at 07:49:27AM +0900, Damien Le Moal wrote:
> On 2/15/22 06:35, Dave Chinner wrote:
> > On Thu, Feb 10, 2022 at 02:59:04PM +0900, Naohiro Aota wrote:
> >> Add an assert function sb_assert_write_started() to check if
> >> sb_start_write() is properly called. It is used in the next commit.
> >>
> >> Also, add the assert functions for sb_start_pagefault() and
> >> sb_start_intwrite().
> >>
> >> Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>
> >> ---
> >>  include/linux/fs.h | 20 ++++++++++++++++++++
> >>  1 file changed, 20 insertions(+)
> >>
> >> diff --git a/include/linux/fs.h b/include/linux/fs.h
> >> index bbf812ce89a8..5d5dc9a276d9 100644
> >> --- a/include/linux/fs.h
> >> +++ b/include/linux/fs.h
> >> @@ -1820,6 +1820,11 @@ static inline bool __sb_start_write_trylock(struct super_block *sb, int level)
> >>  #define __sb_writers_release(sb, lev)	\
> >>  	percpu_rwsem_release(&(sb)->s_writers.rw_sem[(lev)-1], 1, _THIS_IP_)
> >>  
> >> +static inline void __sb_assert_write_started(struct super_block *sb, int level)
> >> +{
> >> +	lockdep_assert_held_read(sb->s_writers.rw_sem + level - 1);
> >> +}
> >> +
> > 
> > So this isn't an assert, it's a WARN_ON(). Asserts stop execution
> > (i.e. kill the task) rather than just issue a warning, so let's not
> > name a function that issues a warning "assert"...
> > 
> > Hence I'd much rather see this implemented as:
> > 
> > static inline bool __sb_write_held(struct super_block *sb, int level)
> > {
> > 	return lockdep_is_held_type(sb->s_writers.rw_sem + level - 1, 1);
> > }
> 
> Since this would be true when called in between __sb_start_write() and
> __sb_end_write(), what about calling it __sb_write_started() ? That
> disconnects from the fact that the implementation uses a sem.

Makes no difference to me; I initially was going to suggest
*_inprogress() but that seemed a bit verbose. We don't need to
bikeshed this to death - all I want is it to be a check that can be
used for generic purposes rather than being an explicit assert.

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com