linux.git/kernel/sched, branch v5.0-rc5

Merge branch 'smp-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2019-02-03T17:02:03+00:00

Pull cpu hotplug fixes from Thomas Gleixner:
 "Two fixes for the cpu hotplug machinery:

   - Replace the overly clever 'SMT disabled by BIOS' detection logic as
     it breaks KVM scenarios and prevents speculation control updates
     when the Hyperthreads are brought online late after boot.

   - Remove a redundant invocation of the speculation control update
     function"

* 'smp-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  cpu/hotplug: Fix "SMT disabled by BIOS" detection for KVM
  x86/speculation: Remove redundant arch_smt_update() invocation

psi: fix aggregation idle shut-off

2019-02-01T23:46:23+00:00

psi has provisions to shut off the periodic aggregation worker when
there is a period of no task activity - and thus no data that needs
aggregating.  However, while developing psi monitoring, Suren noticed
that the aggregation clock currently won't stay shut off for good.

Debugging this revealed a flaw in the idle design: an aggregation run
will see no task activity and decide to go to sleep; shortly thereafter,
the kworker thread that executed the aggregation will go idle and cause
a scheduling change, during which the psi callback will kick the
!pending worker again.  This will ping-pong forever, and is equivalent
to having no shut-off logic at all (but with more code!)

Fix this by exempting aggregation workers from psi's clock waking logic
when the state change is them going to sleep.  To do this, tag workers
with the last work function they executed, and if in psi we see a worker
going to sleep after aggregating psi data, we will not reschedule the
aggregation work item.

What if the worker is also executing other items before or after?

Any psi state times that were incurred by work items preceding the
aggregation work will have been collected from the per-cpu buckets
during the aggregation itself.  If there are work items following the
aggregation work, the worker's last_func tag will be overwritten and the
aggregator will be kept alive to process this genuine new activity.

If the aggregation work is the last thing the worker does, and we decide
to go idle, the brief period of non-idle time incurred between the
aggregation run and the kworker's dequeue will be stranded in the
per-cpu buckets until the clock is woken by later activity.  But that
should not be a problem.  The buckets can hold 4s worth of time, and
future activity will wake the clock with a 2s delay, giving us 2s worth
of data we can leave behind when disabling aggregation.  If it takes a
worker more than two seconds to go idle after it finishes its last work
item, we likely have bigger problems in the system, and won't notice one
sample that was averaged with a bogus per-CPU weight.

Link: http://lkml.kernel.org/r/20190116193501.1910-1-hannes@cmpxchg.org
Fixes: eb414681d5a0 ("psi: pressure stall information for CPU, memory, and IO")
Signed-off-by: Johannes Weiner 
Reported-by: Suren Baghdasaryan 
Acked-by: Tejun Heo 
Cc: Peter Zijlstra 
Cc: Lai Jiangshan 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

cpu/hotplug: Fix "SMT disabled by BIOS" detection for KVM

2019-01-30T18:27:00+00:00

With the following commit:

  73d5e2b47264 ("cpu/hotplug: detect SMT disabled by BIOS")

... the hotplug code attempted to detect when SMT was disabled by BIOS,
in which case it reported SMT as permanently disabled.  However, that
code broke a virt hotplug scenario, where the guest is booted with only
primary CPU threads, and a sibling is brought online later.

The problem is that there doesn't seem to be a way to reliably
distinguish between the HW "SMT disabled by BIOS" case and the virt
"sibling not yet brought online" case.  So the above-mentioned commit
was a bit misguided, as it permanently disabled SMT for both cases,
preventing future virt sibling hotplugs.

Going back and reviewing the original problems which were attempted to
be solved by that commit, when SMT was disabled in BIOS:

  1) /sys/devices/system/cpu/smt/control showed "on" instead of
     "notsupported"; and

  2) vmx_vm_init() was incorrectly showing the L1TF_MSG_SMT warning.

I'd propose that we instead consider #1 above to not actually be a
problem.  Because, at least in the virt case, it's possible that SMT
wasn't disabled by BIOS and a sibling thread could be brought online
later.  So it makes sense to just always default the smt control to "on"
to allow for that possibility (assuming cpuid indicates that the CPU
supports SMT).

The real problem is #2, which has a simple fix: change vmx_vm_init() to
query the actual current SMT state -- i.e., whether any siblings are
currently online -- instead of looking at the SMT "control" sysfs value.

So fix it by:

  a) reverting the original "fix" and its followup fix:

     73d5e2b47264 ("cpu/hotplug: detect SMT disabled by BIOS")
     bc2d8d262cba ("cpu/hotplug: Fix SMT supported evaluation")

     and

  b) changing vmx_vm_init() to query the actual current SMT state --
     instead of the sysfs control value -- to determine whether the L1TF
     warning is needed.  This also requires the 'sched_smt_present'
     variable to exported, instead of 'cpu_smt_control'.

Fixes: 73d5e2b47264 ("cpu/hotplug: detect SMT disabled by BIOS")
Reported-by: Igor Mammedov 
Signed-off-by: Josh Poimboeuf 
Signed-off-by: Thomas Gleixner 
Cc: Joe Mario 
Cc: Jiri Kosina 
Cc: Peter Zijlstra 
Cc: kvm@vger.kernel.org
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/e3a85d585da28cc333ecbc1e78ee9216e6da9396.1548794349.git.jpoimboe@redhat.com

sched/wake_q: Fix wakeup ordering for wake_q

2019-01-21T10:15:37+00:00

Notable cmpxchg() does not provide ordering when it fails, however
wake_q_add() requires ordering in this specific case too. Without this
it would be possible for the concurrent wakeup to not observe our
prior state.

Andrea Parri provided:

  C wake_up_q-wake_q_add

  {
	int next = 0;
	int y = 0;
  }

  P0(int *next, int *y)
  {
	int r0;

	/* in wake_up_q() */

	WRITE_ONCE(*next, 1);   /* node->next = NULL */
	smp_mb();               /* implied by wake_up_process() */
	r0 = READ_ONCE(*y);
  }

  P1(int *next, int *y)
  {
	int r1;

	/* in wake_q_add() */

	WRITE_ONCE(*y, 1);      /* wake_cond = true */
	smp_mb__before_atomic();
	r1 = cmpxchg_relaxed(next, 1, 2);
  }

  exists (0:r0=0 /\ 1:r1=0)

  This "exists" clause cannot be satisfied according to the LKMM:

  Test wake_up_q-wake_q_add Allowed
  States 3
  0:r0=0; 1:r1=1;
  0:r0=1; 1:r1=0;
  0:r0=1; 1:r1=1;
  No
  Witnesses
  Positive: 0 Negative: 3
  Condition exists (0:r0=0 /\ 1:r1=0)
  Observation wake_up_q-wake_q_add Never 0 3

Reported-by: Yongji Xie 
Signed-off-by: Peter Zijlstra (Intel) 
Cc: Davidlohr Bueso 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: Waiman Long 
Cc: Will Deacon 
Signed-off-by: Ingo Molnar

sched/wake_q: Document wake_q_add()

2019-01-21T10:15:36+00:00

The only guarantee provided by wake_q_add() is that a wakeup will
happen after it, it does _NOT_ guarantee the wakeup will be delayed
until the matching wake_up_q().

If wake_q_add() fails the cmpxchg() a concurrent wakeup is pending and
that can happen at any time after the cmpxchg(). This means we should
not rely on the wakeup happening at wake_q_up(), but should be ready
for wake_q_add() to issue the wakeup.

The delay; if provided (most likely); should only result in more efficient
behaviour.

Reported-by: Yongji Xie 
Signed-off-by: Peter Zijlstra (Intel) 
Cc: Davidlohr Bueso 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: Waiman Long 
Cc: Will Deacon 
Signed-off-by: Ingo Molnar

jump_label: move 'asm goto' support test to Kconfig

2019-01-06T00:46:51+00:00

Currently, CONFIG_JUMP_LABEL just means "I _want_ to use jump label".

The jump label is controlled by HAVE_JUMP_LABEL, which is defined
like this:

  #if defined(CC_HAVE_ASM_GOTO) && defined(CONFIG_JUMP_LABEL)
  # define HAVE_JUMP_LABEL
  #endif

We can improve this by testing 'asm goto' support in Kconfig, then
make JUMP_LABEL depend on CC_HAS_ASM_GOTO.

Ugly #ifdef HAVE_JUMP_LABEL will go away, and CONFIG_JUMP_LABEL will
match to the real kernel capability.

Signed-off-by: Masahiro Yamada 
Acked-by: Michael Ellerman  (powerpc)
Tested-by: Sedat Dilek

Merge branch 'akpm' (patches from Andrew)

2019-01-05T17:16:18+00:00

Merge more updates from Andrew Morton:

 - procfs updates

 - various misc bits

 - lib/ updates

 - epoll updates

 - autofs

 - fatfs

 - a few more MM bits

* emailed patches from Andrew Morton : (58 commits)
  mm/page_io.c: fix polled swap page in
  checkpatch: add Co-developed-by to signature tags
  docs: fix Co-Developed-by docs
  drivers/base/platform.c: kmemleak ignore a known leak
  fs: don't open code lru_to_page()
  fs/: remove caller signal_pending branch predictions
  mm/: remove caller signal_pending branch predictions
  arch/arc/mm/fault.c: remove caller signal_pending_branch predictions
  kernel/sched/: remove caller signal_pending branch predictions
  kernel/locking/mutex.c: remove caller signal_pending branch predictions
  mm: select HAVE_MOVE_PMD on x86 for faster mremap
  mm: speed up mremap by 20x on large regions
  mm: treewide: remove unused address argument from pte_alloc functions
  initramfs: cleanup incomplete rootfs
  scripts/gdb: fix lx-version string output
  kernel/kcov.c: mark write_comp_data() as notrace
  kernel/sysctl: add panic_print into sysctl
  panic: add options to print system info when panic happens
  bfs: extra sanity checking and static inode bitmap
  exec: separate MM_ANONPAGES and RLIMIT_STACK accounting
  ...

kernel/sched/: remove caller signal_pending branch predictions

2019-01-04T21:13:48+00:00

This is already done for us internally by the signal machinery.

Link: http://lkml.kernel.org/r/20181116002713.8474-3-dave@stgolabs.net
Signed-off-by: Davidlohr Bueso 
Reviewed-by: Andrew Morton 
Cc: Peter Zijlstra 
Cc: Ingo Molnar 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

Remove 'type' argument from access_ok() function

2019-01-04T02:57:57+00:00

Nobody has actually used the type (VERIFY_READ vs VERIFY_WRITE) argument
of the user address range verification function since we got rid of the
old racy i386-only code to walk page tables by hand.

It existed because the original 80386 would not honor the write protect
bit when in kernel mode, so you had to do COW by hand before doing any
user access.  But we haven't supported that in a long time, and these
days the 'type' argument is a purely historical artifact.

A discussion about extending 'user_access_begin()' to do the range
checking resulted this patch, because there is no way we're going to
move the old VERIFY_xyz interface to that model.  And it's best done at
the end of the merge window when I've done most of my merges, so let's
just get this done once and for all.

This patch was mostly done with a sed-script, with manual fix-ups for
the cases that weren't of the trivial 'access_ok(VERIFY_xyz' form.

There were a couple of notable cases:

 - csky still had the old "verify_area()" name as an alias.

 - the iter_iov code had magical hardcoded knowledge of the actual
   values of VERIFY_{READ,WRITE} (not that they mattered, since nothing
   really used it)

 - microblaze used the type argument for a debug printout

but other than those oddities this should be a total no-op patch.

I tried to fix up all architectures, did fairly extensive grepping for
access_ok() uses, and the changes are trivial, but I may have missed
something.  Any missed conversion should be trivially fixable, though.

Signed-off-by: Linus Torvalds

sched/fair: Fix infinite loop in update_blocked_averages() by reverting a9e7f6544b9c

2018-12-30T12:54:31+00:00

Zhipeng Xie, Xie XiuQi and Sargun Dhillon reported lockups in the
scheduler under high loads, starting at around the v4.18 time frame,
and Zhipeng Xie tracked it down to bugs in the rq->leaf_cfs_rq_list
manipulation.

Do a (manual) revert of:

  a9e7f6544b9c ("sched/fair: Fix O(nr_cgroups) in load balance path")

It turns out that the list_del_leaf_cfs_rq() introduced by this commit
is a surprising property that was not considered in followup commits
such as:

  9c2791f936ef ("sched/fair: Fix hierarchical order in rq->leaf_cfs_rq_list")

As Vincent Guittot explains:

 "I think that there is a bigger problem with commit a9e7f6544b9c and
  cfs_rq throttling:

  Let take the example of the following topology TG2 --> TG1 --> root:

   1) The 1st time a task is enqueued, we will add TG2 cfs_rq then TG1
      cfs_rq to leaf_cfs_rq_list and we are sure to do the whole branch in
      one path because it has never been used and can't be throttled so
      tmp_alone_branch will point to leaf_cfs_rq_list at the end.

   2) Then TG1 is throttled

   3) and we add TG3 as a new child of TG1.

   4) The 1st enqueue of a task on TG3 will add TG3 cfs_rq just before TG1
      cfs_rq and tmp_alone_branch will stay  on rq->leaf_cfs_rq_list.

  With commit a9e7f6544b9c, we can del a cfs_rq from rq->leaf_cfs_rq_list.
  So if the load of TG1 cfs_rq becomes NULL before step 2) above, TG1
  cfs_rq is removed from the list.
  Then at step 4), TG3 cfs_rq is added at the beginning of rq->leaf_cfs_rq_list
  but tmp_alone_branch still points to TG3 cfs_rq because its throttled
  parent can't be enqueued when the lock is released.
  tmp_alone_branch doesn't point to rq->leaf_cfs_rq_list whereas it should.

  So if TG3 cfs_rq is removed or destroyed before tmp_alone_branch
  points on another TG cfs_rq, the next TG cfs_rq that will be added,
  will be linked outside rq->leaf_cfs_rq_list - which is bad.

  In addition, we can break the ordering of the cfs_rq in
  rq->leaf_cfs_rq_list but this ordering is used to update and
  propagate the update from leaf down to root."

Instead of trying to work through all these cases and trying to reproduce
the very high loads that produced the lockup to begin with, simplify
the code temporarily by reverting a9e7f6544b9c - which change was clearly
not thought through completely.

This (hopefully) gives us a kernel that doesn't lock up so people
can continue to enjoy their holidays without worrying about regressions. ;-)

[ mingo: Wrote changelog, fixed weird spelling in code comment while at it. ]

Analyzed-by: Xie XiuQi 
Analyzed-by: Vincent Guittot 
Reported-by: Zhipeng Xie 
Reported-by: Sargun Dhillon 
Reported-by: Xie XiuQi 
Tested-by: Zhipeng Xie 
Tested-by: Sargun Dhillon 
Signed-off-by: Linus Torvalds 
Acked-by: Vincent Guittot 
Cc:  # v4.13+
Cc: Bin Li 
Cc: Mike Galbraith 
Cc: Peter Zijlstra 
Cc: Tejun Heo 
Cc: Thomas Gleixner 
Fixes: a9e7f6544b9c ("sched/fair: Fix O(nr_cgroups) in load balance path")
Link: http://lkml.kernel.org/r/1545879866-27809-1-git-send-email-xiexiuqi@huawei.com
Signed-off-by: Ingo Molnar