[tip:locking/core] locking/refcounts, x86/asm: Disable CONFIG_ARCH_HAS_REFCOUNT for the time being

[tip-bot for Ingo Molnar]

Commit-ID:  7b3d61cc73a1abe4c2c7eaf00093b338c8b233b0
Gitweb:     http://git.kernel.org/tip/7b3d61cc73a1abe4c2c7eaf00093b338c8b233b0
Author:     Ingo Molnar <mingo@xxxxxxxxxx>
AuthorDate: Tue, 29 Aug 2017 13:10:35 +0200
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Tue, 29 Aug 2017 13:10:35 +0200

locking/refcounts, x86/asm: Disable CONFIG_ARCH_HAS_REFCOUNT for the time being

Mike Galbraith bisected a boot crash back to the following commit:

  7a46ec0e2f48 ("locking/refcounts, x86/asm: Implement fast refcount overflow protection")

The crash/hang pattern is:

 > Symptom is a few splats as below, with box finally hanging.  Network
 > comes up, but neither ssh nor console login is possible.
 >
 >  ------------[ cut here ]------------
 >  WARNING: CPU: 4 PID: 0 at net/netlink/af_netlink.c:374 netlink_sock_destruct+0x82/0xa0
 >  ...
 >  __sk_destruct()
 >  rcu_process_callbacks()
 >  __do_softirq()
 >  irq_exit()
 >  smp_apic_timer_interrupt()
 >  apic_timer_interrupt()

We are at -rc7 already, and the code has grown some dependencies, so
instead of a plain revert disable the config temporarily, in the hope
of getting real fixes.

Reported-by: Mike Galbraith <efault@xxxxxx>
Tested-by: Mike Galbraith <efault@xxxxxx>
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: Davidlohr Bueso <dave@xxxxxxxxxxxx>
Cc: Elena Reshetova <elena.reshetova@xxxxxxxxx>
Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/tip-7a46ec0e2f4850407de5e1d19a44edee6efa58ec@xxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 arch/x86/Kconfig | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 6e01f58..efd9df5 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -55,7 +55,8 @@ config X86
 	select ARCH_HAS_KCOV			if X86_64
 	select ARCH_HAS_MMIO_FLUSH
 	select ARCH_HAS_PMEM_API		if X86_64
-	select ARCH_HAS_REFCOUNT
+	# Causing hangs/crashes, see the commit that added this change for details.
+	select ARCH_HAS_REFCOUNT		if BROKEN
 	select ARCH_HAS_UACCESS_FLUSHCACHE	if X86_64
 	select ARCH_HAS_SET_MEMORY
 	select ARCH_HAS_SG_CHAIN