lkml.org 
[lkml]   [2012]   [Jun]   [11]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    SubjectRe: rcu: endless stalls
    From
    Date
    On Mon, 2012-06-11 at 11:01 -0700, Paul E. McKenney wrote: 
    > On Mon, Jun 11, 2012 at 07:20:14PM +0200, Mike Galbraith wrote:
    > > On Mon, 2012-06-11 at 16:22 +0200, Mike Galbraith wrote:
    > > > On Mon, 2012-06-11 at 06:39 -0700, Paul E. McKenney wrote:
    > > > > On Mon, Jun 11, 2012 at 12:06:16PM +0200, Mike Galbraith wrote:
    > > > > > Greetings,
    > > > > >
    > > > > > I received a report of a 48 core UV box hitting a gripe, taking longer
    > > > > > than timeout to emit same, so box griped endlessly, forcing reboot.
    > > > >
    > > > > So it took minutes to print an RCU CPU stall warning? On only 48 CPUs?
    > > > >
    > > > > If so, yow!!!
    > > >
    > > > The report was a tad fuzzy on details, but serial console can take a
    > > > while at low baud rate, and the box was apparently perma-stalled.
    > >
    > > Gee, no wonder it took a while to emit the gripe, there were a few more
    > > than 48 CPUs actually.. 4048 more to be precise.
    > >
    > > 4096 tasks on 4096 CPUs all hammering wait_lock at once r!pretty.
    >
    > That would be bad...
    >
    > BTW, one other thing on the patch -- it needs to use a separate flag,
    > otherwise there are races with sysfs and panic() updates to the flag.
    >
    > > 2aa15890 - mm: prevent concurrent unmap_mapping_range() on the same inode
    >
    > I confess, you lost me on this one. You believe that this commit is
    > the cause of the RCU CPU stall warnings?

    4096 tasks on 4096 CPUs exit (well, try to) simultaneously.

    Call Trace:
    __mutex_lock_slowpath+0x94/0x150
    mutex_lock+0x1a/0x40
    unlink_file_vma+0x3f/0xf0
    free_pgtables+0x40/0x100
    exit_mmap+0xb0/0x120
    mmput+0x49/0x120
    exit_mm+0x122/0x160
    do_exit+0x179/0x8d0
    do_group_exit+0x3d/0xb0
    sys_exit_group+0x12/0x20

    Monster box dies screaming.

    -Mike



    \
     
     \ /
      Last update: 2012-06-11 20:42    [W:0.026 / U:0.064 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site