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From: Colin Ian King <colin.king@canonical.com>
To: "Paul E. McKenney" <paulmck@linux.ibm.com>,
	Josh Triplett <josh@joshtriplett.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
	Lai Jiangshan <jiangshanlai@gmail.com>,
	Joel Fernandes <joel@joelfernandes.org>,
	rcu@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Subject: re: rcu/nocb: Add bypass callback queueing, bug report
Date: Tue, 13 Aug 2019 13:34:02 +0100	[thread overview]
Message-ID: <e89f5af3-dcf3-986f-828f-14e10cef9915@canonical.com> (raw)

Hi,

Static analysis on linux-next today found an issue in the following commit:

commit 1afc4b18724f8f7b7a21fdf66cd43cc4a932812d
Author: Paul E. McKenney <paulmck@linux.ibm.com>
Date:   Tue Jul 2 16:03:33 2019 -0700

    rcu/nocb: Add bypass callback queueing


The coverity report is as follows:

1783        // If we have advanced to a new jiffy, reset counts to allow
1784        // moving back from ->nocb_bypass to ->cblist.
1785        if (j == rdp->nocb_nobypass_last) {
1786                c = rdp->nocb_nobypass_count + 1;
1787        } else {
1788                WRITE_ONCE(rdp->nocb_nobypass_last, j);
1789                c = rdp->nocb_nobypass_count -
nocb_nobypass_lim_per_jiffy;
1790                if (c > nocb_nobypass_lim_per_jiffy)
1791                        c = nocb_nobypass_lim_per_jiffy;

CID 85141 (#1 of 1): Unsigned compared against 0
unsigned_compare: This less-than-zero comparison of an unsigned value is
never true. c < 0UL.

1792                else if (c < 0)
1793                        c = 0;

Variable c is an unsigned long so the c < 0 check is never true. I'm not
sure what the ramifications are if c is made a signed long instead, so
I'm not fixing this and reporting this issue.

Regards,

Colin

             reply	other threads:[~2019-08-13 12:34 UTC|newest]

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-13 12:34 Colin Ian King [this message]
2019-08-13 15:23 ` rcu/nocb: Add bypass callback queueing, bug report Paul E. McKenney

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