linux-kernel - [PATCH] [RESEND] [v2] iopoll: avoid -Wint-in-bool-context warning

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Date:   Thu,  2 Nov 2017 12:40:36 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Arnd Bergmann <arnd@...db.de>, Mark Brown <broonie@...nel.org>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH] [RESEND] [v2] iopoll: avoid -Wint-in-bool-context warning

When we pass the result of a multiplication as the timeout or the delay,
we can get a warning from gcc-7:

drivers/mmc/host/bcm2835.c:596:149: error: '*' in boolean context, suggest '&&' instead [-Werror=int-in-bool-context]
drivers/mfd/arizona-core.c:247:195: error: '*' in boolean context, suggest '&&' instead [-Werror=int-in-bool-context]
drivers/gpu/drm/sun4i/sun4i_hdmi_i2c.c:49:27: error: '*' in boolean context, suggest '&&' instead [-Werror=int-in-bool-context]

The warning is a bit questionable inside of a macro, but this is
intentional on the side of the gcc developers.  It is also an indication
of another problem: we evaluate the timeout and sleep arguments multiple
times, which can have undesired side-effects when those are complex
expressions.

This changes the two iopoll variants to use local variables for storing
copies of the timeouts.  This adds some more type safety, and avoids both
the double-evaluation and the gcc warning.

Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81484
Link: http://lkml.kernel.org/r/20170726133756.2161367-1-arnd@arndb.de
Reviewed-by: Mark Brown <broonie@...nel.org>
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
v2: the v1 patch was in mmotm since I first posted it, but it gained a
conflict on the regmap header and got dropped. I've split it in two
patches now as Mark originally suggested, only the iopoll patch should
need to go through mmotm this time, while Mark has already picked up
the other half.
---
 include/linux/iopoll.h | 24 +++++++++++++++---------
 1 file changed, 15 insertions(+), 9 deletions(-)

diff --git a/include/linux/iopoll.h b/include/linux/iopoll.h
index d29e1e21bf3f..b1d861caca16 100644
--- a/include/linux/iopoll.h
+++ b/include/linux/iopoll.h
@@ -42,18 +42,21 @@
  */
 #define readx_poll_timeout(op, addr, val, cond, sleep_us, timeout_us)	\
 ({ \
-	ktime_t timeout = ktime_add_us(ktime_get(), timeout_us); \
-	might_sleep_if(sleep_us); \
+	u64 __timeout_us = (timeout_us); \
+	unsigned long __sleep_us = (sleep_us); \
+	ktime_t __timeout = ktime_add_us(ktime_get(), __timeout_us); \
+	might_sleep_if((__sleep_us) != 0); \
 	for (;;) { \
 		(val) = op(addr); \
 		if (cond) \
 			break; \
-		if (timeout_us && ktime_compare(ktime_get(), timeout) > 0) { \
+		if (__timeout_us && \
+		    ktime_compare(ktime_get(), __timeout) > 0) { \
 			(val) = op(addr); \
 			break; \
 		} \
-		if (sleep_us) \
-			usleep_range((sleep_us >> 2) + 1, sleep_us); \
+		if (__sleep_us) \
+			usleep_range((__sleep_us >> 2) + 1, __sleep_us); \
 	} \
 	(cond) ? 0 : -ETIMEDOUT; \
 })
@@ -77,17 +80,20 @@
  */
 #define readx_poll_timeout_atomic(op, addr, val, cond, delay_us, timeout_us) \
 ({ \
-	ktime_t timeout = ktime_add_us(ktime_get(), timeout_us); \
+	u64 __timeout_us = (timeout_us); \
+	unsigned long __delay_us = (delay_us); \
+	ktime_t __timeout = ktime_add_us(ktime_get(), __timeout_us); \
 	for (;;) { \
 		(val) = op(addr); \
 		if (cond) \
 			break; \
-		if (timeout_us && ktime_compare(ktime_get(), timeout) > 0) { \
+		if (__timeout_us && \
+		    ktime_compare(ktime_get(), __timeout) > 0) { \
 			(val) = op(addr); \
 			break; \
 		} \
-		if (delay_us) \
-			udelay(delay_us);	\
+		if (__delay_us) \
+			udelay(__delay_us);	\
 	} \
 	(cond) ? 0 : -ETIMEDOUT; \
 })
-- 
2.9.0