linux-kernel - [PATCH] lkdtm: Fix race when crashpoint is hit multiple times before checking count

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Message-Id: <1308094827-29684-1-git-send-email-johunt@akamai.com>
Date:	Tue, 14 Jun 2011 16:40:27 -0700
From:	Josh Hunt <johunt@...mai.com>
To:	Ankita Garg <ankita@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org, Tapan Dhimant <tdhimant@...mai.com>
Subject: [PATCH] lkdtm: Fix race when crashpoint is hit multiple times before checking count

We observed the crash point count going negative in cases where the crash point
is hit multiple times before the check of "count == 0" is done. Because of this
we never call lkdtm_do_action(). This patch just adds a spinlock to protect
count.

Reported-by: Tapan Dhimant <tdhimant@...mai.com>
Signed-off-by: Josh Hunt <johunt@...mai.com>
---
 drivers/misc/lkdtm.c |    8 ++++++++
 1 files changed, 8 insertions(+), 0 deletions(-)

diff --git a/drivers/misc/lkdtm.c b/drivers/misc/lkdtm.c
index 81d7fa4..150cd70 100644
--- a/drivers/misc/lkdtm.c
+++ b/drivers/misc/lkdtm.c
@@ -120,6 +120,7 @@ static int recur_count = REC_NUM_DEFAULT;
 static enum cname cpoint = CN_INVALID;
 static enum ctype cptype = CT_NONE;
 static int count = DEFAULT_COUNT;
+static DEFINE_SPINLOCK(count_lock);
 
 module_param(recur_count, int, 0644);
 MODULE_PARM_DESC(recur_count, " Recursion level for the stack overflow test, "\
@@ -230,11 +231,14 @@ static const char *cp_name_to_str(enum cname name)
 static int lkdtm_parse_commandline(void)
 {
 	int i;
+	unsigned long flags;
 
 	if (cpoint_count < 1 || recur_count < 1)
 		return -EINVAL;
 
+	spin_lock_irqsave(&count_lock, flags);
 	count = cpoint_count;
+	spin_unlock_irqrestore(&count_lock, flags);
 
 	/* No special parameters */
 	if (!cpoint_type && !cpoint_name)
@@ -349,6 +353,9 @@ static void lkdtm_do_action(enum ctype which)
 
 static void lkdtm_handler(void)
 {
+	unsigned long flags;
+
+	spin_lock_irqsave(&count_lock, flags);
 	count--;
 	printk(KERN_INFO "lkdtm: Crash point %s of type %s hit, trigger in %d rounds\n",
 			cp_name_to_str(cpoint), cp_type_to_str(cptype), count);
@@ -357,6 +364,7 @@ static void lkdtm_handler(void)
 		lkdtm_do_action(cptype);
 		count = cpoint_count;
 	}
+	spin_unlock_irqrestore(&count_lock, flags);
 }
 
 static int lkdtm_register_cpoint(enum cname which)
-- 
1.7.0.4

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