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From:   Nathan Chancellor <natechancellor@gmail.com>
To:     Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Cc:     "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        intel-wired-lan@lists.osuosl.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com,
        Nathan Chancellor <natechancellor@gmail.com>
Subject: [PATCH] igc: Do not use link uninitialized in igc_check_for_copper_link
Date:   Wed, 15 Jul 2020 21:49:34 -0700
Message-Id: <20200716044934.152364-1-natechancellor@gmail.com>
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Sender: linux-kernel-owner@vger.kernel.org
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Clang warns:

drivers/net/ethernet/intel/igc/igc_mac.c:374:6: warning: variable 'link'
is used uninitialized whenever 'if' condition is true
[-Wsometimes-uninitialized]
        if (!mac->get_link_status) {
            ^~~~~~~~~~~~~~~~~~~~~
drivers/net/ethernet/intel/igc/igc_mac.c:424:33: note: uninitialized use
occurs here
        ret_val = igc_set_ltr_i225(hw, link);
                                       ^~~~
drivers/net/ethernet/intel/igc/igc_mac.c:374:2: note: remove the 'if' if
its condition is always false
        if (!mac->get_link_status) {
        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/net/ethernet/intel/igc/igc_mac.c:367:11: note: initialize the
variable 'link' to silence this warning
        bool link;
                 ^
                  = 0
1 warning generated.

It is not wrong, link is only uninitialized after this through
igc_phy_has_link. Presumably, if we skip the majority of this function
when get_link_status is false, we should skip calling igc_set_ltr_i225
as well. Just directly return 0 in this case, rather than bothering with
adding another label or initializing link in the if statement.

Fixes: 707abf069548 ("igc: Add initial LTR support")
Link: https://github.com/ClangBuiltLinux/linux/issues/1095
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
---
 drivers/net/ethernet/intel/igc/igc_mac.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ethernet/intel/igc/igc_mac.c b/drivers/net/ethernet/intel/igc/igc_mac.c
index b47e7b0a6398..26e3c56a4a8b 100644
--- a/drivers/net/ethernet/intel/igc/igc_mac.c
+++ b/drivers/net/ethernet/intel/igc/igc_mac.c
@@ -371,10 +371,8 @@ s32 igc_check_for_copper_link(struct igc_hw *hw)
 	 * get_link_status flag is set upon receiving a Link Status
 	 * Change or Rx Sequence Error interrupt.
 	 */
-	if (!mac->get_link_status) {
-		ret_val = 0;
-		goto out;
-	}
+	if (!mac->get_link_status)
+		return 0;
 
 	/* First we want to see if the MII Status Register reports
 	 * link.  If so, then we want to get the current speed/duplex

base-commit: ca0e494af5edb59002665bf12871e94b4163a257
-- 
2.28.0.rc0