Re: [PATCH v19 32/40] completion, dept: introduce init_completion_dmap() API

On Tue, Jul 07, 2026 at 07:33:49AM +0000, [email protected] wrote:
> Thank you for your contribution! Sashiko AI review found 3 potential issue(s) to consider:
> - [High] Double evaluation of arguments in wait_for_completion macros leads to skipped array indices and memory corruption.
> - [Medium] Unconditional struct growth of a widely used primitive for a debug feature.
> - [Medium] Wait event macros skip calling sdt_might_sleep_end() on signal interruptions, leaking DEPT tracking state and stacks.
> --
> 
> commit 5b626a37ee940081b6d37187cde51c2f272e370c
> Author: Byungchul Park <[email protected]>
> 
> completion, dept: introduce init_completion_dmap() API
> 
> Currently, dept uses dept's map embedded in task_struct to track
> dependencies related to wait_for_completion() and its family.  So it
> doesn't need an explicit map basically.
> 
> However, for those who want to set the maps with customized class or
> key, introduce a new API to use external maps.
> 
> > diff --git a/include/linux/completion.h b/include/linux/completion.h
> > index 4d8fb1d95c0a6..e50f7d9b4b974 100644
> > --- a/include/linux/completion.h
> > +++ b/include/linux/completion.h
> > @@ -27,17 +27,15 @@
> >  struct completion {
> >       unsigned int done;
> >       struct swait_queue_head wait;
> > +     struct dept_map *dmap;
> >  };
> 
> [Severity: Medium]
> Since struct completion is heavily embedded in many kernel data structures,
> does unconditionally adding the dmap pointer increase the global memory
> footprint even on production non-debug kernels? Should this new field be
> guarded by an #ifdef?

Good point.  I will fix it, but with dkey.  It will look like:

+   struct dept_key_ptr dkey_ptr;

> [ ... ]
> 
> > @@ -136,13 +140,13 @@ extern void complete_all(struct completion *);
> >
> >  #define wait_for_completion(x)                                               \
> >  ({                                                                   \
> > -     sdt_might_sleep_start_timeout(NULL, -1L);                       \
> > +     sdt_might_sleep_start_timeout((x)->dmap, -1L);                  \
> >       __wait_for_completion(x);                                       \
> >       sdt_might_sleep_end();                                          \
> >  })
> 
> [Severity: High]
> Does evaluating the argument x multiple times in this macro lead to issues
> if callers pass an expression with side effects?
> 
> For example, if a caller like mlx5_vdpa_exec_async_cmds() does:
> 
>         while (completed < issued)
>                 wait_for_completion(&cmds[completed++].cmd_done);
> 
> Would completed++ be executed twice per iteration, skipping array elements
> and potentially causing out-of-bounds memory accesses?

Sure.  I will fix it.

> [ ... ]
> 
> [Severity: Medium]
> Do wait event macros such as ___wait_event() in include/linux/wait.h skip
> calling sdt_might_sleep_end() when interrupted by a signal?
> 
> In include/linux/wait.h:___wait_event():
> 
>                 if (___wait_is_interruptible(state) && __int) { \
>                         __ret = __int; \
>                         goto __out; \
>                 }
>         ...
>         sdt_might_sleep_end(); \
> __out:  __ret; \
> })
> 
> If the wait is interrupted by a signal, it escapes via goto __out. Because
> __out is placed after sdt_might_sleep_end(), it seems the cleanup is
> skipped.
> 
> Does this permanently leak the tracking state and its underlying stack
> objects?

I will fix it.

	Byungchul

> --
> Sashiko AI review · https://sashiko.dev/#/patchset/[email protected]?part=32