linux-kernel - [PATCH 3.12 56/86] ACPI / power: Avoid maybe-uninitialized warning

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Message-Id: <b082138e968867c56fb7e6ca84548f81af03489a.1493888632.git.jslaby@suse.cz>
Date:   Thu,  4 May 2017 11:04:21 +0200
From:   Jiri Slaby <jslaby@...e.cz>
To:     stable@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 56/86] ACPI / power: Avoid maybe-uninitialized warning

From: Arnd Bergmann <arnd@...db.de>

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

commit fe8c470ab87d90e4b5115902dd94eced7e3305c3 upstream.

gcc -O2 cannot always prove that the loop in acpi_power_get_inferred_state()
is enterered at least once, so it assumes that cur_state might not get
initialized:

drivers/acpi/power.c: In function 'acpi_power_get_inferred_state':
drivers/acpi/power.c:222:9: error: 'cur_state' may be used uninitialized in this function [-Werror=maybe-uninitialized]

This sets the variable to zero at the start of the loop, to ensure that
there is well-defined behavior even for an empty list. This gets rid of
the warning.

The warning first showed up when the -Os flag got removed in a bug fix
patch in linux-4.11-rc5.

I would suggest merging this addon patch on top of that bug fix to avoid
introducing a new warning in the stable kernels.

Fixes: 61b79e16c68d (ACPI: Fix incompatibility with mcount-based function graph tracing)
Signed-off-by: Arnd Bergmann <arnd@...db.de>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 drivers/acpi/power.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/acpi/power.c b/drivers/acpi/power.c
index c2ad391d8041..4b35a115749c 100644
--- a/drivers/acpi/power.c
+++ b/drivers/acpi/power.c
@@ -204,6 +204,7 @@ static int acpi_power_get_list_state(struct list_head *list, int *state)
 		return -EINVAL;
 
 	/* The state of the list is 'on' IFF all resources are 'on'. */
+	cur_state = 0;
 	list_for_each_entry(entry, list, node) {
 		struct acpi_power_resource *resource = entry->resource;
 		acpi_handle handle = resource->device.handle;
-- 
2.12.2