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From:   Nicholas Mc Guire <hofrat@osadl.org>
To:     Jason Cooper <jason@lakedaemon.net>
Cc:     Andrew Lunn <andrew@lunn.ch>,
        Gregory Clement <gregory.clement@bootlin.com>,
        Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>,
        Russell King <linux@armlinux.org.uk>,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        Nicholas Mc Guire <hofrat@osadl.org>
Subject: [PATCH V2] ARM: mvebu: at least report the kzalloc failure
Date:   Tue, 16 Apr 2019 05:56:31 +0200
Message-Id: <1555386991-8855-1-git-send-email-hofrat@osadl.org>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Although it is very unlikely that the allocation during init would
fail any such failure should point to the original cause to allow
easier understanding of the ensuing null-pointer dereference splat.

Signed-off-by: Nicholas Mc Guire <hofrat@osadl.org>
---

Problem located with experimental coccinelle script

V2: Russell King <linux@armlinux.org.uk> pointed out that the use of
    WARN_ON() would result in a stack trace followed by the oops due
    to dereferencing of the NULL pointer and so make it even less
    likely that users would uncover the actual cause - so drop the
    WARN_ON() and use a short pr_err() message that points to the
    oops cause directly.

Note that this will trigger a checkpatch WARNING
"WARNING: Possible unnecessary 'out of memory' message"
but comparing the oops with an without the one-line pr_err I would
argue that it makes sense to include it:
<snip>
[ 8061.514840] shared page allocation failure in hello_init()
[ 8113.563239] BUG: unable to handle kernel NULL pointer dereference at 0000000000000000
[ 8113.563250] #PF error: [WRITE]
[ 8113.563255] PGD 8000000129993067 P4D 8000000129993067 PUD 129992067 PMD 0
[ 8113.563267] Oops: 0002 [#1] SMP PTI
[ 8113.563276] CPU: 2 PID: 2656 Comm: bash Tainted: G        W  O      5.0.0-rc3livepatchtest-next-20190123+ #4
[ 8113.563280] Hardware name: Quanta TWH/TWH, BIOS QU221 10/14/2011
[ 8113.563292] RIP: 0010:foo_store+0x3a/0x90 [hello_chardev]
...
<snip>

Patch was compile-tested: mvebu_v7_defconfig (implies MACH_MVEBU_ANY=y)
(with some unrelated sparse warnings about missing syscalls)

Patch is against 5.1-rc4 (localversion-next is 20190415)

 arch/arm/mach-mvebu/board-v7.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/arm/mach-mvebu/board-v7.c b/arch/arm/mach-mvebu/board-v7.c
index 0b10acd..df84cb6 100644
--- a/arch/arm/mach-mvebu/board-v7.c
+++ b/arch/arm/mach-mvebu/board-v7.c
@@ -128,6 +128,9 @@ static void __init i2c_quirk(void)
 		struct property *new_compat;
 
 		new_compat = kzalloc(sizeof(*new_compat), GFP_KERNEL);
+		if (!new_compat)
+			pr_err("new_compat allocation failure in %s()\n",
+				__func__);
 
 		new_compat->name = kstrdup("compatible", GFP_KERNEL);
 		new_compat->length = sizeof("marvell,mv78230-a0-i2c");
-- 
2.1.4