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

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.
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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?

[ ... ]

> @@ -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?

[ ... ]

[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?

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