[PATCH v4 2/4] Makefile/coccicheck: speed up and fix bug with duplicate hunks

Change the coccicheck target to run on all of our *.c and *.h files with --include-headers-for-types, instead of trusting it to find *.h files and other includes to modify from its recursive walking of includes as it has been doing with only --all-includes.

The --all-includes option introduced in a9a884aea57 (coccicheck: use --all-includes by default, 2016-09-30) is needed because we have rules that e.g. use the "type T" construct that wouldn't match unless we scoured our headers for the definition of the relevant type.

But combining --all-includes it with processing N files at a time with xargs as we've done since 960154b9c17 (coccicheck: optionally batch spatch invocations, 2019-05-06) introduced a subtle bug with duplicate hunks being written to the generated *.patch files. I did not dig down to the root cause of that, but I think it's due to spatch doing (and failing to do) some magical locking/racy mtime checking to decide if it emits a hunk. See [1] for a way to reproduce the issue, and a discussion of it.

This change speeds up the runtime of "make -j8 coccicheck" from ~1m50s to ~1m20s for me. See [2] for more timings.

We could also use --no-includes for a runtime of ~55s, but that would produce broken patches (we miss some hunks) in cases where we need the type or other definitions from included files.

If anyone cares there's probably an optimization opportunity here to e.g. detect that the whole file doesn't need to consider includes, since the rules would be unambiguous without considering them.

Note on portability: The --include-headers-for-types option is not in my "man spatch", but it's been part of spatch since 2014. See its fe3a327a (include headers for types option, 2014-07-27), it was first released with version 1.0.0 of spatch, released in April 2015. The spatch developers are just inconsistent about updating their TeX docs and manpages at the same time.

1. https://lore.kernel.org/git/20210305170724.23859-3-avarab@gmail.com/
2. https://lore.kernel.org/git/20210306192525.15197-1-avarab@gmail.com/

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
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 Makefile | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)