linux-kernel - [PATCH 2/5 v2] Modify behaviour of request_*muxed

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Date:   Thu, 22 Jun 2017 15:21:31 +0200
From:   Zoltán Böszörményi 
        <zboszor@...hu>
To:     linux-kernel@...r.kernel.org
Cc:     linux-usb@...r.kernel.org, linux-watchdog@...r.kernel.org,
        linux-i2c@...r.kernel.org,
        Paul Menzel <paulepanter@...rs.sourceforge.net>,
        Christian Fetzer <fetzer.ch@...il.com>,
        Jean Delvare <jdelvare@...e.com>,
        Nehal Shah <nehal-bakulchandra.shah@....com>,
        Tim Small <tim@...ss.co.uk>,
        Guenter Roeck <linux@...ck-us.net>, kernel@...ss.net,
        wim@...ana.be, jlayton@...chiereds.net, marc.2377@...il.com,
        cshorler@...glemail.com, wsa@...-dreams.de,
        regressions@...mhuis.info,
        Zoltán Böszörményi 
        <zboszor@...hu>
Subject: [PATCH 2/5 v2] Modify behaviour of request_*muxed_region()

In order to make request_*muxed_region() behave more like
mutex_lock(), a possible failure case needs to be eliminated.
When drivers do not properly share the same I/O region, e.g.
one is using request_region() and the other is using
request_muxed_region(), the kernel didn't warn the user about it.
This change modifies IORESOURCE_MUXED behaviour so it always
goes to sleep waiting for the resuorce to be freed and the
inconsistent resource flag usage is logged with KERN_ERR.

v2: Fixed checkpatch.pl warnings and extended the comment
    about request_declared_muxed_region.

Signed-off-by: Zoltán Böszörményi <zboszor@...hu>
---
 kernel/resource.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/kernel/resource.c b/kernel/resource.c
index 2be7029..5df2731 100644
--- a/kernel/resource.c
+++ b/kernel/resource.c
@@ -1125,6 +1125,7 @@ resource_size_t resource_alignment(struct resource *res)
  *
  * request_declared_muxed_region creates a new shared busy region
  * described in an existing resource descriptor.
+ * It only returns if it succeeded.
  *
  * release_region releases a matching busy region.
  * The region is only freed if it was allocated.
@@ -1191,7 +1192,10 @@ struct resource *__request_declared_region(struct resource *parent,
 				continue;
 			}
 		}
-		if (conflict->flags & flags & IORESOURCE_MUXED) {
+		if (flags & IORESOURCE_MUXED) {
+			if (!(conflict->flags & IORESOURCE_MUXED))
+				pr_err("Resource conflict between muxed \"%s\" and non-muxed \"%s\" I/O regions!\n",
+					res->name, conflict->name);
 			add_wait_queue(&muxed_resource_wait, &wait);
 			write_unlock(&resource_lock);
 			set_current_state(TASK_UNINTERRUPTIBLE);
-- 
2.9.4