Messages in this thread Patch in this message | | | Date | Mon, 16 Oct 2017 11:28:43 -0700 | From | "Luck, Tony" <> | Subject | Re: x86/mce: suspicious RCU usage in 4.13.4 |
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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
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); }
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