linux-kernel - [smatch] sched_fair: check after dereference

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Message-ID: <20101220061041.GA8512@bicker>
Date:	Mon, 20 Dec 2010 09:10:41 +0300
From:	Dan Carpenter <error27@...il.com>
To:	Paul Turner <pjt@...gle.com>
Cc:	Peter Zijlstra <peterz@...radead.org>, linux-kernel@...r.kernel.org
Subject: [smatch] sched_fair: check after dereference

Hi Paul,

In linux-next e33078baa4 "sched: Fix update_cfs_load() synchronization"
introduced a dereference before the check for NULL.  I don't know the
code well enough to say if it's a bug or if the check can be removed.

kernel/sched_fair.c +728 update_cfs_load(6)
	warn: variable dereferenced before check 'cfs_rq'

   722  static void update_cfs_load(struct cfs_rq *cfs_rq, int global_update)
   723  {
   724          u64 period = sysctl_sched_shares_window;
   725          u64 now, delta;
   726          unsigned long load = cfs_rq->load.weight;
                                     ^^^^^^^^^^^^^^^^^^^
   727
   728          if (!cfs_rq)
                     ^^^^^^
   729                  return;

Can you take a look?

regards,
dan carpenter

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