From: "Luck, Tony" <tony.luck@intel.com>
To: Borislav Petkov <bp@alien8.de>
Cc: Andi Kleen <ak@linux.intel.com>, Jeremy Cline <jcline@redhat.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
"x86@kernel.org" <x86@kernel.org>,
"linux-edac@vger.kernel.org" <linux-edac@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Laura Abbott <labbott@redhat.com>
Subject: x86/mce: suspicious RCU usage in 4.13.4
Date: Mon, 16 Oct 2017 11:28:43 -0700 [thread overview]
Message-ID: <20171016182843.wrtcelsqf2y2onze@intel.com> (raw)
On Sun, Oct 15, 2017 at 11:40:46AM +0200, Borislav Petkov wrote:
> On Wed, Oct 11, 2017 at 09:34:22PM +0000, Luck, Tony wrote:
> > > here's a second attempt at a more rigorous simplification: RCU stuff is
> > > gone and only a single loop scans through the elements.
> >
> > The dev_mce_log() changes look good now.
> >
> > You can apply the axe to more bits of mce_chrdev_read() though. Like that
>
> That provoked a very serious axing. Please check whether I went too far. Hunk
> below is ontop of what got axed already:
I think a few more lines can go. Almost everything relating to the "finished"
element. dev_mce_log() must still set it (because the user mode mcelog(8)
daemon will grumble if we give it records that don't have it set). But
since everything is protected by mce_chrdev_read_mutex we can't have
"Old left over entries" to skip. Nor is there any way that finished can't
be set for an entry in 0..mcelog.next when it comes to mce_chrdev_read().
This patch on top of your two???
-Tony
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diff --git a/arch/x86/kernel/cpu/mcheck/dev-mcelog.c b/arch/x86/kernel/cpu/mcheck/dev-mcelog.c
index 17d2bab25720..7f85b76f43bc 100644
--- a/arch/x86/kernel/cpu/mcheck/dev-mcelog.c
+++ b/arch/x86/kernel/cpu/mcheck/dev-mcelog.c
@@ -49,11 +49,7 @@ static int dev_mce_log(struct notifier_block *nb, unsigned long val,
mutex_lock(&mce_chrdev_read_mutex);
- for (entry = mcelog.next; entry < MCE_LOG_LEN; entry++) {
- /* Old left over entry. Skip: */
- if (mcelog.entry[entry].finished)
- continue;
- }
+ entry = mcelog.next;
/*
* When the buffer fills up discard new entries. Assume that the
@@ -231,9 +227,6 @@ static ssize_t mce_chrdev_read(struct file *filp, char __user *ubuf,
for (i = 0; i < next; i++) {
struct mce *m = &mcelog.entry[i];
- if (!m->finished)
- continue;
-
err |= copy_to_user(buf, m, sizeof(*m));
buf += sizeof(*m);
}
next reply other threads:[~2017-10-16 18:28 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-10-16 18:28 Luck, Tony [this message]
-- strict thread matches above, loose matches on Subject: below --
2017-11-01 20:07 x86/mce: suspicious RCU usage in 4.13.4 Luck, Tony
2017-11-01 16:47 Borislav Petkov
2017-11-01 14:56 Laura Abbott
2017-10-15 9:40 Borislav Petkov
2017-10-12 22:13 Andi Kleen
2017-10-12 9:02 Borislav Petkov
2017-10-11 23:11 Andi Kleen
2017-10-11 21:34 Luck, Tony
2017-10-11 11:50 Borislav Petkov
2017-10-10 20:13 Andi Kleen
2017-10-10 20:08 Luck, Tony
2017-10-10 19:44 Borislav Petkov
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