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Revision 706a1ea65e6faaf853427a0e931f59d604dd45e3 authored by Linus Torvalds on 23 August 2018, 21:55:01 UTC, committed by Linus Torvalds on 23 August 2018, 21:55:01 UTC 
Merge branch 'tlb-fixes'
 
Merge fixes for missing TLB shootdowns.

This fixes a couple of cases that involved us possibly freeing page
table structures before the required TLB shootdown had been done.

There are a few cleanup patches to make the code easier to follow, and
to avoid some of the more problematic cases entirely when not necessary.

To make this easier for backports, it undoes the recent lazy TLB
patches, because the cleanups and fixes are more important, and Rik is
ok with re-doing them later when things have calmed down.

The missing TLB flush was only delayed, and the wrong ordering only
happened under memory pressure (and in theory under a couple of other
fairly theoretical situations), so this may have been all very unlikely
to have hit people in practice.

But getting the TLB shootdown wrong is _so_ hard to debug and see that I
consider this a crticial fix.

Many thanks to Jann Horn for having debugged this.

* tlb-fixes:
  x86/mm: Only use tlb_remove_table() for paravirt
  mm: mmu_notifier fix for tlb_end_vma
  mm/tlb, x86/mm: Support invalidating TLB caches for RCU_TABLE_FREE
  mm/tlb: Remove tlb_remove_table() non-concurrent condition
  mm: move tlb_table_flush to tlb_flush_mmu_free
  x86/mm/tlb: Revert the recent lazy TLB patches
2 parent s d40acad + 48a8b97
Raw File
atomic_bitops.txt 

On atomic bitops.


While our bitmap_{}() functions are non-atomic, we have a number of operations
operating on single bits in a bitmap that are atomic.


API
---

The single bit operations are:

Non-RMW ops:

  test_bit()

RMW atomic operations without return value:

  {set,clear,change}_bit()
  clear_bit_unlock()

RMW atomic operations with return value:

  test_and_{set,clear,change}_bit()
  test_and_set_bit_lock()

Barriers:

  smp_mb__{before,after}_atomic()


All RMW atomic operations have a '__' prefixed variant which is non-atomic.


SEMANTICS
---------

Non-atomic ops:

In particular __clear_bit_unlock() suffers the same issue as atomic_set(),
which is why the generic version maps to clear_bit_unlock(), see atomic_t.txt.


RMW ops:

The test_and_{}_bit() operations return the original value of the bit.


ORDERING
--------

Like with atomic_t, the rule of thumb is:

 - non-RMW operations are unordered;

 - RMW operations that have no return value are unordered;

 - RMW operations that have a return value are fully ordered.

 - RMW operations that are conditional are unordered on FAILURE,
   otherwise the above rules apply. In the case of test_and_{}_bit() operations,
   if the bit in memory is unchanged by the operation then it is deemed to have
   failed.

Except for a successful test_and_set_bit_lock() which has ACQUIRE semantics and
clear_bit_unlock() which has RELEASE semantics.

Since a platform only has a single means of achieving atomic operations
the same barriers as for atomic_t are used, see atomic_t.txt.
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