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d72da4a4d9
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Peter Zijlstra d72da4a4d9 rbtree: Make lockless searches non-fatal 
Change the insert and erase code such that lockless searches are
non-fatal.

In and of itself an rbtree cannot be correctly searched while
in-modification, we can however provide weaker guarantees that will
allow the rbtree to be used in conjunction with other techniques, such
as latches; see 9b0fd802e8 ("seqcount: Add raw_write_seqcount_latch()").

For this to work we need the following guarantees from the rbtree
code:

 1) a lockless reader must not see partial stores, this would allow it
    to observe nodes that are invalid memory.

 2) there must not be (temporary) loops in the tree structure in the
    modifier's program order, this would cause a lookup which
    interrupts the modifier to get stuck indefinitely.

For 1) we must use WRITE_ONCE() for all updates to the tree structure;
in particular this patch only does rb_{left,right} as those are the
only element required for simple searches.

It generates slightly worse code, probably because volatile. But in
pointer chasing heavy code a few instructions more should not matter.

For 2) I have carefully audited the code and drawn every intermediate
link state and not found a loop.

Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: David Woodhouse <David.Woodhouse@intel.com>
Cc: Rik van Riel <riel@redhat.com>
Reviewed-by: Michel Lespinasse <walken@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
2015-05-28 11:32:04 +09:30
..
acpi ACPICA: remove duplicate u8 typedef 2015-04-28 23:58:54 +02:00
asm-generic TTY/Serial patches for 4.1-rc1 2015-04-21 09:33:10 -07:00
clocksource
crypto Merge git://git.kernel.org/pub/scm/linux/kernel/git/herbert/crypto-2.6 2015-04-15 10:42:15 -07:00
drm drm/radeon: add new bonaire pci id 2015-05-12 13:42:46 -04:00
dt-bindings Merge branch 'for-linus' of git://git.infradead.org/users/vkoul/slave-dma 2015-04-24 09:49:37 -07:00
keys
kvm KVM/ARM changes for v4.1: 2015-04-07 18:09:20 +02:00
linux rbtree: Make lockless searches non-fatal 2015-05-28 11:32:04 +09:30
math-emu
media Merge branch 'patchwork' into v4l_for_linus 2015-04-21 06:12:35 -03:00
memory
misc
net inet: properly align icsk_ca_priv 2015-05-19 11:08:00 -04:00
pcmcia
ras
rdma IB/core: Fix unaligned accesses 2015-05-05 13:21:27 -04:00
rxrpc RxRPC: Handle VERSION Rx protocol packets 2015-04-01 16:31:26 +01:00
scsi SCSI: add 1024 max sectors black list flag 2015-04-27 09:38:06 -07:00
soc
sound ASoC: Fixes for v4.1 2015-04-30 19:08:06 +02:00
target Merge branch 'for-next' of git://git.kernel.org/pub/scm/linux/kernel/git/nab/target-pending 2015-04-24 10:22:09 -07:00
trace Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2015-04-26 17:22:07 -07:00
uapi Merge git://git.kernel.org/pub/scm/linux/kernel/git/pablo/nf 2015-05-16 16:40:22 -04:00
video fbdev changes for v4.1 2015-04-20 15:16:25 -07:00
xen xen/events: don't bind non-percpu VIRQs with percpu chip 2015-05-19 19:55:36 +01:00
Kbuild