FROMLIST: locking/rwsem: Add __always_inline annotation to...

FROMLIST: locking/rwsem: Add __always_inline annotation to __down_write_common() and inlined callers

Apparently despite it being marked inline, the compiler
may not inline __down_write_common() which makes it difficult
to identify the cause of lock contention, as the wchan of the
blocked function will always be listed as __down_write_common().

So add __always_inline annotation to the common function (as
well as the inlined helper callers) to force it to be inlined
so a more useful blocking function will be listed (via wchan).

This mirrors commit 92cc5d00 ("locking/rwsem: Add
__always_inline annotation to __down_read_common() and inlined
callers") which did the same for __down_read_common.

I sort of worry that I'm playing wack-a-mole here, and talking
with compiler people, they tell me inline means nothing, which
makes me want to cry a little. So I'm wondering if we need to
replace all the inlines with __always_inline, or remove them
because either we mean something by it, or not.

Cc: Tim Murray <timmurray@google.com>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Will Deacon <will@kernel.org>
Cc: Waiman Long <longman@redhat.com>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: kernel-team@android.com
Fixes: c995e638 ("locking/rwsem: Fold __down_{read,write}*()")
Reported-by: Tim Murray <timmurray@google.com>
Acked-by: Waiman Long <longman@redhat.com>
Change-Id: I72b273149577b8125ea3a5053befbd5cf66bf8ad
Signed-off-by: John Stultz <jstultz@google.com>
Link: https://lore.kernel.org/lkml/20240620174204.1802235-1-jstultz@google.com/
Bug: 332722989
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v2:
* Add ack tags & minor tweaks to commit message