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  1. Aug 06, 2014
  3. Aug 05, 2014
  5. Jul 29, 2014
  7. Jul 28, 2014
  9. Jul 27, 2014
    • Linus Torvalds's avatar
      Fix gcc-4.9.0 miscompilation of load_balance() in scheduler · 2062afb4
      Linus Torvalds authored 
      Michel Dänzer and a couple of other people reported inexplicable random
oopses in the scheduler, and the cause turns out to be gcc mis-compiling
the load_balance() function when debugging is enabled.  The gcc bug
apparently goes back to gcc-4.5, but slight optimization changes means
that it now showed up as a problem in 4.9.0 and 4.9.1.

The instruction scheduling problem causes gcc to schedule a spill
operation to before the stack frame has been created, which in turn can
corrupt the spilled value if an interrupt comes in.  There may be other
effects of this bug too, but that's the code generation problem seen in
Michel's case.

This is fixed in current gcc HEAD, but the workaround as suggested by
Markus Trippelsdorf is pretty simple: use -fno-var-tracking-assignments
when compiling the kernel, which disables the gcc code that causes the
problem.  This can result in slightly worse debug information for
variable accesses, but that is infinitely preferable to actual code
generation problems.

Doing this unconditionally (not just for CONFIG_DEBUG_INFO) also allows
non-debug builds to verify that the debug build would be identical: we
can do

    export GCC_COMPARE_DEBUG=1

to make gcc internally verify that the result of the build is
independent of the "-g" flag (it will make the compiler build everything
twice, toggling the debug flag, and compare the results).

Without the "-fno-var-tracking-assignments" option, the build would fail
(even with 4.8.3 that didn't show the actual stack frame bug) with a gcc
compare failure.

See also gcc bugzilla:

  https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61801



Reported-by: default avatarMichel Dänzer <michel@daenzer.net>
Suggested-by: default avatarMarkus Trippelsdorf <markus@trippelsdorf.de>
Cc: Jakub Jelinek <jakub@redhat.com>
Cc: stable@kernel.org
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      2062afb4
    • Hugh Dickins's avatar
      mm: fix direct reclaim writeback regression · 8bdd6380
      Hugh Dickins authored 
      Shortly before 3.16-rc1, Dave Jones reported:

  WARNING: CPU: 3 PID: 19721 at fs/xfs/xfs_aops.c:971
           xfs_vm_writepage+0x5ce/0x630 [xfs]()
  CPU: 3 PID: 19721 Comm: trinity-c61 Not tainted 3.15.0+ #3
  Call Trace:
    xfs_vm_writepage+0x5ce/0x630 [xfs]
    shrink_page_list+0x8f9/0xb90
    shrink_inactive_list+0x253/0x510
    shrink_lruvec+0x563/0x6c0
    shrink_zone+0x3b/0x100
    shrink_zones+0x1f1/0x3c0
    try_to_free_pages+0x164/0x380
    __alloc_pages_nodemask+0x822/0xc90
    alloc_pages_vma+0xaf/0x1c0
    handle_mm_fault+0xa31/0xc50
  etc.

 970   if (WARN_ON_ONCE((current->flags & (PF_MEMALLOC|PF_KSWAPD)) ==
 971                   PF_MEMALLOC))

I did not respond at the time, because a glance at the PageDirty block
in shrink_page_list() quickly shows that this is impossible: we don't do
writeback on file pages (other than tmpfs) from direct reclaim nowadays.
Dave was hallucinating, but it would have been disrespectful to say so.

However, my own /var/log/messages now shows similar complaints

  WARNING: CPU: 1 PID: 28814 at fs/ext4/inode.c:1881 ext4_writepage+0xa7/0x38b()
  WARNING: CPU: 0 PID: 27347 at fs/ext4/inode.c:1764 ext4_writepage+0xa7/0x38b()

from stressing some mmotm trees during July.

Could a dirty xfs or ext4 file page somehow get marked PageSwapBacked,
so fail shrink_page_list()'s page_is_file_cache() test, and so proceed
to mapping->a_ops->writepage()?

Yes, 3.16-rc1's commit 68711a74

 ("mm, migration: add destination
page freeing callback") has provided such a way to compaction: if
migrating a SwapBacked page fails, its newpage may be put back on the
list for later use with PageSwapBacked still set, and nothing will clear
it.

Whether that can do anything worse than issue WARN_ON_ONCEs, and get
some statistics wrong, is unclear: easier to fix than to think through
the consequences.

Fixing it here, before the put_new_page(), addresses the bug directly,
but is probably the worst place to fix it.  Page migration is doing too
many parts of the job on too many levels: fixing it in
move_to_new_page() to complement its SetPageSwapBacked would be
preferable, except why is it (and newpage->mapping and newpage->index)
done there, rather than down in migrate_page_move_mapping(), once we are
sure of success? Not a cleanup to get into right now, especially not
with memcg cleanups coming in 3.17.

Reported-by: default avatarDave Jones <davej@redhat.com>
Signed-off-by: default avatarHugh Dickins <hughd@google.com>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      8bdd6380
  11. Jul 26, 2014
  13. Jul 25, 2014
    • H. Peter Anvin's avatar
      x86: Merge tag 'ras_urgent' into x86/urgent · bf72f5de
      H. Peter Anvin authored 
      Promote one fix for 3.16

This fix was necessary after

9c15a24b ("x86/mce: Improve mcheck_init_device() error handling")

went in. What this patch did was, among others, check the return value
of misc_register and exit early if it encountered an error. Original
code sloppily didn't do that.

However,

        cef12ee5

 ("xen/mce: Add mcelog support for Xen platform")

made it so that xen's init routine xen_late_init_mcelog runs first. This
was needed for the xen mcelog device which is supposed to be independent
from the baremetal one.

Initially it was reported that misc_register() fails often on xen and
that's why it needed fixing. However, it is *supposed* to fail by
design, when running in dom0 so that the xen mcelog device file gets
registered first.

And *then* you need the notifier *not* unregistered on the error path so
that the timer does get deleted properly in the CPU hotplug notifier.

Btw, this fix is needed also on baremetal in the unlikely event that
misc_register(&mce_chrdev_device) fails there too.

I was unsure whether to rush it in now and decided to delay it to 3.17.
However, xen people wanted it promoted as it breaks xen when doing cpu
hotplug there. So, after a bit of simmering in tip/master for initial
smoke testing, let's move it to 3.16. It fixes a semi-regression which
got introduced in 3.16 so no need for stable tagging.

tip/x86/ras contains that exact same commit but we can't remove it
there as it is not the last one. It won't cause any merge issues, as I
confirmed locally but I should state here the special situation of this
one fix explicitly anyway.

Thanks.

Signed-off-by: default avatarH. Peter Anvin <hpa@linux.intel.com>
      bf72f5de
    • Jerome Glisse's avatar
      drm/radeon: fix cut and paste issue for hawaii. · 1b2c4869
      Jerome Glisse authored 
      

This is a halfway fix for hawaii acceleration. More fixes to come
but hopefully isolated to userspace.

Signed-off-by: default avatarJérôme Glisse <jglisse@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: default avatarDave Airlie <airlied@redhat.com>
      1b2c4869
    • Dave Airlie's avatar
      Merge branch 'drm-fixes-3.16' of git://people.freedesktop.org/~agd5f/linux into drm-fixes · 97cefc3e
      Dave Airlie authored 
      two more radeon fixes.

* 'drm-fixes-3.16' of git://people.freedesktop.org/~agd5f/linux:
  drm/radeon: fix irq ring buffer overflow handling
  drm/radeon: fix error handling in radeon_vm_bo_set_addr
      97cefc3e
    • Dave Airlie's avatar
      Merge tag 'drm-intel-fixes-2014-07-24' of git://anongit.freedesktop.org/drm-intel into drm-fixes · 9d6ed3c6
      Dave Airlie authored 
      This time in time! Just 32bit-pae fix from Hugh, semaphores fun from Chris
and a fix for runtime pm cherry-picked from next.

Paulo is still working on a fix for runtime pm when X does cursor fun when
the display is off, but that one isn't ready yet.

* tag 'drm-intel-fixes-2014-07-24' of git://anongit.freedesktop.org/drm-intel:
  drm/i915: Simplify i915_gem_release_all_mmaps()
  drm/i915: fix freeze with blank screen booting highmem
  drm/i915: Reorder the semaphore deadlock check, again
      9d6ed3c6
    • HIMANGI SARAOGI's avatar
      parisc: Eliminate memset after alloc_bootmem_pages · 9794144d
      HIMANGI SARAOGI authored 
      

alloc_bootmem and related function always return zeroed region of
memory. Thus a memset after calls to these functions is unnecessary.

The following Coccinelle semantic patch was used for making the change:

@@
expression E,E1;
@@

E = \(alloc_bootmem\|alloc_bootmem_low\|alloc_bootmem_pages\|alloc_bootmem_low_pages\)(...)
... when != E
- memset(E,0,E1);

Signed-off-by: default avatarHimangi Saraogi <himangi774@gmail.com>
Acked-by: default avatarJulia Lawall <julia.lawall@lip6.fr>
Signed-off-by: default avatarHelge Deller <deller@gmx.de>
      9794144d