linux-kernel - [RFC PATCH 57/86] coccinelle: script to remove cond

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Message-Id: <20231107230822.371443-1-ankur.a.arora@oracle.com>
Date:   Tue,  7 Nov 2023 15:07:53 -0800
From:   Ankur Arora <ankur.a.arora@...cle.com>
To:     linux-kernel@...r.kernel.org
Cc:     tglx@...utronix.de, peterz@...radead.org,
        torvalds@...ux-foundation.org, paulmck@...nel.org,
        linux-mm@...ck.org, x86@...nel.org, akpm@...ux-foundation.org,
        luto@...nel.org, bp@...en8.de, dave.hansen@...ux.intel.com,
        hpa@...or.com, mingo@...hat.com, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, willy@...radead.org, mgorman@...e.de,
        jon.grimm@....com, bharata@....com, raghavendra.kt@....com,
        boris.ostrovsky@...cle.com, konrad.wilk@...cle.com,
        jgross@...e.com, andrew.cooper3@...rix.com, mingo@...nel.org,
        bristot@...nel.org, mathieu.desnoyers@...icios.com,
        geert@...ux-m68k.org, glaubitz@...sik.fu-berlin.de,
        anton.ivanov@...bridgegreys.com, mattst88@...il.com,
        krypton@...ich-teichert.org, rostedt@...dmis.org,
        David.Laight@...LAB.COM, richard@....at, mjguzik@...il.com,
        Ankur Arora <ankur.a.arora@...cle.com>,
        Julia Lawall <Julia.Lawall@...ia.fr>,
        Nicolas Palix <nicolas.palix@...g.fr>
Subject: [RFC PATCH 57/86] coccinelle: script to remove cond_resched()

Rudimentary script to remove the straight-forward subset of
cond_resched() and allies:

1)  if (need_resched())
	  cond_resched()

2)  expression*;
    cond_resched();  /* or in the reverse order */

3)  if (expression)
	statement
    cond_resched();  /* or in the reverse order */

The last two patterns depend on the control flow level to ensure
that the complex cond_resched() patterns (ex. conditioned ones)
are left alone and we only pick up ones which are only minimally
related the neighbouring code.

Cc: Julia Lawall <Julia.Lawall@...ia.fr>
Cc: Nicolas Palix <nicolas.palix@...g.fr>
Signed-off-by: Ankur Arora <ankur.a.arora@...cle.com>
---
 scripts/coccinelle/api/cond_resched.cocci | 53 +++++++++++++++++++++++
 1 file changed, 53 insertions(+)
 create mode 100644 scripts/coccinelle/api/cond_resched.cocci

diff --git a/scripts/coccinelle/api/cond_resched.cocci b/scripts/coccinelle/api/cond_resched.cocci
new file mode 100644
index 000000000000..bf43768a8f8c
--- /dev/null
+++ b/scripts/coccinelle/api/cond_resched.cocci
@@ -0,0 +1,53 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/// Remove naked cond_resched() statements
+///
+//# Remove cond_resched() statements when:
+//#   - executing at the same control flow level as the previous or the
+//#     next statement (this lets us avoid complicated conditionals in
+//#     the neighbourhood.)
+//#   - they are of the form "if (need_resched()) cond_resched()" which
+//#     is always safe.
+//#
+//# Coccinelle generally takes care of comments in the immediate neighbourhood
+//# but might need to handle other comments alluding to rescheduling.
+//#
+virtual patch
+virtual context
+
+@ r1 @
+identifier r;
+@@
+
+(
+ r = cond_resched();
+|
+-if (need_resched())
+-	cond_resched();
+)
+
+@ r2 @
+expression E;
+statement S,T;
+@@
+(
+ E;
+|
+ if (E) S
+|
+ if (E) S else T
+|
+)
+-cond_resched();
+
+@ r3 @
+expression E;
+statement S,T;
+@@
+-cond_resched();
+(
+ E;
+|
+ if (E) S
+|
+ if (E) S else T
+)
-- 
2.31.1