From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from hera.kernel.org ([140.211.167.34]) by bombadil.infradead.org with esmtps (Exim 4.72 #1 (Red Hat Linux)) id 1Oxw62-00029K-JH for kexec@lists.infradead.org; Tue, 21 Sep 2010 06:12:54 +0000 Message-ID: <4C984D27.3050102@kernel.org> Date: Tue, 21 Sep 2010 08:13:59 +0200 From: Tejun Heo MIME-Version: 1.0 Subject: [PATCH] percpu: fix pcpu_last_unit_cpu References: <1848241872.1438141285029613564.JavaMail.root@zmail06.collab.prod.int.phx2.redhat.com> In-Reply-To: <1848241872.1438141285029613564.JavaMail.root@zmail06.collab.prod.int.phx2.redhat.com> List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: kexec-bounces@lists.infradead.org Errors-To: kexec-bounces+dwmw2=infradead.org@lists.infradead.org To: CAI Qian , lkml Cc: graff yang , Marcelo Tosatti , kexec , linux-kernel , dhowells@redhat.com, sonic adi , Chris Lalancette , Avi Kivity pcpu_first/last_unit_cpu are used to track which cpu has the first and last units assigned. This in turn is used to determine the span of a chunk for man/unmap cache flushes and whether an address belongs to the first chunk or not in per_cpu_ptr_to_phys(). When the number of possible CPUs isn't power of two, a chunk may contain unassigned units towards the end of a chunk. The logic to determine pcpu_last_unit_cpu was incorrect when there was an unused unit at the end of a chunk. It failed to ignore the unused unit and assigned the unused marker NR_CPUS to pcpu_last_unit_cpu. This was discovered through kdump failure which was caused by malfunctioning per_cpu_ptr_to_phys() on a kvm setup with 50 possible CPUs by CAI Qian. Signed-off-by: Tejun Heo Reported-by: CAI Qian Cc: stable@kernel.org --- This is pretty subtle and has the potential to cause mysterious problems on vcache architectuers. Thanks a lot for discovering it and your patience. I'll put it out in linux-next for a couple of days and push it to Linus and stable. Thanks. mm/percpu.c | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-) diff --git a/mm/percpu.c b/mm/percpu.c index 58c572b..c76ef38 100644 --- a/mm/percpu.c +++ b/mm/percpu.c @@ -1401,9 +1401,9 @@ int __init pcpu_setup_first_chunk(const struct pcpu_alloc_info *ai, if (pcpu_first_unit_cpu == NR_CPUS) pcpu_first_unit_cpu = cpu; + pcpu_last_unit_cpu = cpu; } } - pcpu_last_unit_cpu = cpu; pcpu_nr_units = unit; for_each_possible_cpu(cpu) -- 1.7.1 _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec