lkml.org 
[lkml]   [2017]   [Nov]   [1]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    SubjectRe: x86/mce: suspicious RCU usage in 4.13.4
    From
    Date
    On 10/16/2017 11:28 AM, Luck, Tony wrote:
    > 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???
    >

    Did these get queued up somewhere? I know last week was OSSEU/Ksummit
    so people may still be playing catch-up.

    Thanks,
    Laura

    > -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);
    > }
    >

    \
     
     \ /
      Last update: 2017-11-01 15:57    [W:6.393 / U:0.040 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site