Re: [PATCH v19 31/40] dept: assign unique dept_key to each distinct wait_for_completion() caller

[Byungchul Park <byungchul@sk.com>]

On Tue, Jul 07, 2026 at 03:18:29PM +0100, Gary Guo wrote:
> On Mon Jul 6, 2026 at 7:19 AM BST, Byungchul Park wrote:
> > wait_for_completion() can be used at various points in the code and it's
> > very hard to distinguish wait_for_completion()s between different usages.
> > Using a single dept_key for all the wait_for_completion()s could trigger
> > false positive reports.
> >
> > Assign unique dept_key to each distinct wait_for_completion() caller to
> > avoid false positive reports.
> >
> > While at it, add a rust helper for wait_for_completion() to avoid build
> > errors.
> 
> This will cause Rust code to share the same dept_key, so it will have all the
> false positives that the change is trying to avoid.

Thank you for the input.

> In general it is easy to create Rust bindings for static inline C functions
> because it'll be just some computation, while creating bindings for C
> function-like macros that define additional statics can be challenging.
> 
> Is dept_key similar to lock_class_key, where only the address matters? If so,
> the approach that I use in
> https://lore.kernel.org/rust-for-linux/DJP0CDOR98N5.29BK8PUFRWRUK@garyguo.net

Yes, dept_key is similar to lock_class_key.  IIUC, the way you tried for
lock_class_key can be applied to DEPT too.  I will do:

   1) add 'key' parameter to sdt_might_sleep_start_timeout()
   2) introduce init_completion_dkey() to allow custom keys
   3) remove init_completion_dmap() and adjust the existing users

Just in case, it's worth noting that the custom keys must be
well-managed using e.g. dept_key_destroy() when the key gets freed.

	Byungchul

> could be used for dept_key as well, then we can keep Rust `wait_for_completion`
> still a function; otherwise we have to turn it into a macro too on the Rust side
> to create such statics, which isn't ideal.
> 
> Best,
> Gary
> 
> >
> > Signed-off-by: Byungchul Park <byungchul@sk.com>
> > ---
> >  include/linux/completion.h | 100 +++++++++++++++++++++++++++++++------
> >  kernel/sched/completion.c  |  60 +++++++++++-----------
> >  rust/helpers/completion.c  |   5 ++
> >  3 files changed, 120 insertions(+), 45 deletions(-)