<feed xmlns='http://www.w3.org/2005/Atom'>
<title>linux-toradex.git/arch/powerpc, branch v3.0.84</title>
<subtitle>Linux kernel for Apalis and Colibri modules</subtitle>
<link rel='alternate' type='text/html' href='https://git.toradex.cn/cgit/linux-toradex.git/'/>
<entry>
<title>powerpc: fix numa distance for form0 device tree</title>
<updated>2013-05-11T20:38:00+00:00</updated>
<author>
<name>Vaidyanathan Srinivasan</name>
<email>svaidy@linux.vnet.ibm.com</email>
</author>
<published>2013-03-22T05:49:35+00:00</published>
<link rel='alternate' type='text/html' href='https://git.toradex.cn/cgit/linux-toradex.git/commit/?id=5013bcf5cbd6969b8873b964e0d7aaab430cf643'/>
<id>5013bcf5cbd6969b8873b964e0d7aaab430cf643</id>
<content type='text'>
commit 7122beeee7bc1757682049780179d7c216dd1c83 upstream.

The following commit breaks numa distance setup for old powerpc
systems that use form0 encoding in device tree.

commit 41eab6f88f24124df89e38067b3766b7bef06ddb
powerpc/numa: Use form 1 affinity to setup node distance

Device tree node /rtas/ibm,associativity-reference-points would
index into /cpus/PowerPCxxxx/ibm,associativity based on form0 or
form1 encoding detected by ibm,architecture-vec-5 property.

All modern systems use form1 and current kernel code is correct.
However, on older systems with form0 encoding, the numa distance
will get hard coded as LOCAL_DISTANCE for all nodes.  This causes
task scheduling anomaly since scheduler will skip building numa
level domain (topmost domain with all cpus) if all numa distances
are same.  (value of 'level' in sched_init_numa() will remain 0)

Prior to the above commit:
((from) == (to) ? LOCAL_DISTANCE : REMOTE_DISTANCE)

Restoring compatible behavior with this patch for old powerpc systems
with device tree where numa distance are encoded as form0.

Signed-off-by: Vaidyanathan Srinivasan &lt;svaidy@linux.vnet.ibm.com&gt;
Signed-off-by: Michael Ellerman &lt;michael@ellerman.id.au&gt;
Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;

</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
commit 7122beeee7bc1757682049780179d7c216dd1c83 upstream.

The following commit breaks numa distance setup for old powerpc
systems that use form0 encoding in device tree.

commit 41eab6f88f24124df89e38067b3766b7bef06ddb
powerpc/numa: Use form 1 affinity to setup node distance

Device tree node /rtas/ibm,associativity-reference-points would
index into /cpus/PowerPCxxxx/ibm,associativity based on form0 or
form1 encoding detected by ibm,architecture-vec-5 property.

All modern systems use form1 and current kernel code is correct.
However, on older systems with form0 encoding, the numa distance
will get hard coded as LOCAL_DISTANCE for all nodes.  This causes
task scheduling anomaly since scheduler will skip building numa
level domain (topmost domain with all cpus) if all numa distances
are same.  (value of 'level' in sched_init_numa() will remain 0)

Prior to the above commit:
((from) == (to) ? LOCAL_DISTANCE : REMOTE_DISTANCE)

Restoring compatible behavior with this patch for old powerpc systems
with device tree where numa distance are encoded as form0.

Signed-off-by: Vaidyanathan Srinivasan &lt;svaidy@linux.vnet.ibm.com&gt;
Signed-off-by: Michael Ellerman &lt;michael@ellerman.id.au&gt;
Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;

</pre>
</div>
</content>
</entry>
<entry>
<title>powerpc/spufs: Initialise inode-&gt;i_ino in spufs_new_inode()</title>
<updated>2013-05-08T02:57:21+00:00</updated>
<author>
<name>Michael Ellerman</name>
<email>michael@ellerman.id.au</email>
</author>
<published>2013-04-23T15:13:14+00:00</published>
<link rel='alternate' type='text/html' href='https://git.toradex.cn/cgit/linux-toradex.git/commit/?id=ea70316c0e035731348f6be194e6332388944029'/>
<id>ea70316c0e035731348f6be194e6332388944029</id>
<content type='text'>
commit 6747e83235caecd30b186d1282e4eba7679f81b7 upstream.

In commit 85fe402 (fs: do not assign default i_ino in new_inode), the
initialisation of i_ino was removed from new_inode() and pushed down
into the callers. However spufs_new_inode() was not updated.

This exhibits as no files appearing in /spu, because all our dirents
have a zero inode, which readdir() seems to dislike.

Signed-off-by: Michael Ellerman &lt;michael@ellerman.id.au&gt;
Signed-off-by: Benjamin Herrenschmidt &lt;benh@kernel.crashing.org&gt;
Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;

</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
commit 6747e83235caecd30b186d1282e4eba7679f81b7 upstream.

In commit 85fe402 (fs: do not assign default i_ino in new_inode), the
initialisation of i_ino was removed from new_inode() and pushed down
into the callers. However spufs_new_inode() was not updated.

This exhibits as no files appearing in /spu, because all our dirents
have a zero inode, which readdir() seems to dislike.

Signed-off-by: Michael Ellerman &lt;michael@ellerman.id.au&gt;
Signed-off-by: Benjamin Herrenschmidt &lt;benh@kernel.crashing.org&gt;
Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;

</pre>
</div>
</content>
</entry>
<entry>
<title>powerpc: Add isync to copy_and_flush</title>
<updated>2013-05-08T02:57:20+00:00</updated>
<author>
<name>Michael Neuling</name>
<email>michael.neuling@au1.ibm.com</email>
</author>
<published>2013-04-24T00:30:09+00:00</published>
<link rel='alternate' type='text/html' href='https://git.toradex.cn/cgit/linux-toradex.git/commit/?id=74f31cf3c186bc0189ad560fadfc03dd9aa2f806'/>
<id>74f31cf3c186bc0189ad560fadfc03dd9aa2f806</id>
<content type='text'>
commit 29ce3c5073057991217916abc25628e906911757 upstream.

In __after_prom_start we copy the kernel down to zero in two calls to
copy_and_flush.  After the first call (copy from 0 to copy_to_here:)
we jump to the newly copied code soon after.

Unfortunately there's no isync between the copy of this code and the
jump to it.  Hence it's possible that stale instructions could still be
in the icache or pipeline before we branch to it.

We've seen this on real machines and it's results in no console output
after:
  calling quiesce...
  returning from prom_init

The below adds an isync to ensure that the copy and flushing has
completed before any branching to the new instructions occurs.

Signed-off-by: Michael Neuling &lt;mikey@neuling.org&gt;
Signed-off-by: Benjamin Herrenschmidt &lt;benh@kernel.crashing.org&gt;
Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;

</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
commit 29ce3c5073057991217916abc25628e906911757 upstream.

In __after_prom_start we copy the kernel down to zero in two calls to
copy_and_flush.  After the first call (copy from 0 to copy_to_here:)
we jump to the newly copied code soon after.

Unfortunately there's no isync between the copy of this code and the
jump to it.  Hence it's possible that stale instructions could still be
in the icache or pipeline before we branch to it.

We've seen this on real machines and it's results in no console output
after:
  calling quiesce...
  returning from prom_init

The below adds an isync to ensure that the copy and flushing has
completed before any branching to the new instructions occurs.

Signed-off-by: Michael Neuling &lt;mikey@neuling.org&gt;
Signed-off-by: Benjamin Herrenschmidt &lt;benh@kernel.crashing.org&gt;
Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;

</pre>
</div>
</content>
</entry>
<entry>
<title>powerpc: pSeries_lpar_hpte_remove fails from Adjunct partition being performed before the ANDCOND test</title>
<updated>2013-04-12T16:18:09+00:00</updated>
<author>
<name>Michael Wolf</name>
<email>mjw@linux.vnet.ibm.com</email>
</author>
<published>2013-04-05T10:41:40+00:00</published>
<link rel='alternate' type='text/html' href='https://git.toradex.cn/cgit/linux-toradex.git/commit/?id=8a7adba6f5b486e00f03d88d185a25ec4c1b6175'/>
<id>8a7adba6f5b486e00f03d88d185a25ec4c1b6175</id>
<content type='text'>
commit 9fb2640159f9d4f5a2a9d60e490482d4cbecafdb upstream.

Some versions of pHyp will perform the adjunct partition test before the
ANDCOND test.  The result of this is that H_RESOURCE can be returned and
cause the BUG_ON condition to occur. The HPTE is not removed.  So add a
check for H_RESOURCE, it is ok if this HPTE is not removed as
pSeries_lpar_hpte_remove is looking for an HPTE to remove and not a
specific HPTE to remove.  So it is ok to just move on to the next slot
and try again.

Signed-off-by: Michael Wolf &lt;mjw@linux.vnet.ibm.com&gt;
Signed-off-by: Stephen Rothwell &lt;sfr@canb.auug.org.au&gt;
Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;

</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
commit 9fb2640159f9d4f5a2a9d60e490482d4cbecafdb upstream.

Some versions of pHyp will perform the adjunct partition test before the
ANDCOND test.  The result of this is that H_RESOURCE can be returned and
cause the BUG_ON condition to occur. The HPTE is not removed.  So add a
check for H_RESOURCE, it is ok if this HPTE is not removed as
pSeries_lpar_hpte_remove is looking for an HPTE to remove and not a
specific HPTE to remove.  So it is ok to just move on to the next slot
and try again.

Signed-off-by: Michael Wolf &lt;mjw@linux.vnet.ibm.com&gt;
Signed-off-by: Stephen Rothwell &lt;sfr@canb.auug.org.au&gt;
Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;

</pre>
</div>
</content>
</entry>
<entry>
<title>signal: Define __ARCH_HAS_SA_RESTORER so we know whether to clear sa_restorer</title>
<updated>2013-04-05T17:16:35+00:00</updated>
<author>
<name>Ben Hutchings</name>
<email>ben@decadent.org.uk</email>
</author>
<published>2012-11-26T03:24:19+00:00</published>
<link rel='alternate' type='text/html' href='https://git.toradex.cn/cgit/linux-toradex.git/commit/?id=1c190534db77a019936d95a1826a55bf34d7ed23'/>
<id>1c190534db77a019936d95a1826a55bf34d7ed23</id>
<content type='text'>
Vaguely based on upstream commit 574c4866e33d 'consolidate kernel-side
struct sigaction declarations'.

flush_signal_handlers() needs to know whether sigaction::sa_restorer
is defined, not whether SA_RESTORER is defined.  Define the
__ARCH_HAS_SA_RESTORER macro to indicate this.

Signed-off-by: Ben Hutchings &lt;ben@decadent.org.uk&gt;
Cc: Al Viro &lt;viro@zeniv.linux.org.uk&gt;
Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;

</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
Vaguely based on upstream commit 574c4866e33d 'consolidate kernel-side
struct sigaction declarations'.

flush_signal_handlers() needs to know whether sigaction::sa_restorer
is defined, not whether SA_RESTORER is defined.  Define the
__ARCH_HAS_SA_RESTORER macro to indicate this.

Signed-off-by: Ben Hutchings &lt;ben@decadent.org.uk&gt;
Cc: Al Viro &lt;viro@zeniv.linux.org.uk&gt;
Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;

</pre>
</div>
</content>
</entry>
<entry>
<title>powerpc: Fix cputable entry for 970MP rev 1.0</title>
<updated>2013-03-20T19:58:52+00:00</updated>
<author>
<name>Benjamin Herrenschmidt</name>
<email>benh@kernel.crashing.org</email>
</author>
<published>2013-03-12T22:55:02+00:00</published>
<link rel='alternate' type='text/html' href='https://git.toradex.cn/cgit/linux-toradex.git/commit/?id=99c817e4571710eca014345ac44c5ba41e77a853'/>
<id>99c817e4571710eca014345ac44c5ba41e77a853</id>
<content type='text'>
commit d63ac5f6cf31c8a83170a9509b350c1489a7262b upstream.

Commit 44ae3ab3358e962039c36ad4ae461ae9fb29596c forgot to update
the entry for the 970MP rev 1.0 processor when moving some CPU
features bits to the MMU feature bit mask. This breaks booting
on some rare G5 models using that chip revision.

Reported-by: Phileas Fogg &lt;phileas-fogg@mail.ru&gt;
Signed-off-by: Benjamin Herrenschmidt &lt;benh@kernel.crashing.org&gt;
Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;

</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
commit d63ac5f6cf31c8a83170a9509b350c1489a7262b upstream.

Commit 44ae3ab3358e962039c36ad4ae461ae9fb29596c forgot to update
the entry for the 970MP rev 1.0 processor when moving some CPU
features bits to the MMU feature bit mask. This breaks booting
on some rare G5 models using that chip revision.

Reported-by: Phileas Fogg &lt;phileas-fogg@mail.ru&gt;
Signed-off-by: Benjamin Herrenschmidt &lt;benh@kernel.crashing.org&gt;
Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;

</pre>
</div>
</content>
</entry>
<entry>
<title>powerpc/kexec: Disable hard IRQ before kexec</title>
<updated>2013-02-28T14:32:26+00:00</updated>
<author>
<name>Phileas Fogg</name>
<email>phileas-fogg@mail.ru</email>
</author>
<published>2013-02-22T23:32:19+00:00</published>
<link rel='alternate' type='text/html' href='https://git.toradex.cn/cgit/linux-toradex.git/commit/?id=534aaed9080ba82974e8d2a71e43a362918138f8'/>
<id>534aaed9080ba82974e8d2a71e43a362918138f8</id>
<content type='text'>
commit 8520e443aa56cc157b015205ea53e7b9fc831291 upstream.

Disable hard IRQ before kexec a new kernel image.
Not doing it can result in corrupted data in the memory segments
reserved for the new kernel.

Signed-off-by: Phileas Fogg &lt;phileas-fogg@mail.ru&gt;
Signed-off-by: Benjamin Herrenschmidt &lt;benh@kernel.crashing.org&gt;
Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;

</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
commit 8520e443aa56cc157b015205ea53e7b9fc831291 upstream.

Disable hard IRQ before kexec a new kernel image.
Not doing it can result in corrupted data in the memory segments
reserved for the new kernel.

Signed-off-by: Phileas Fogg &lt;phileas-fogg@mail.ru&gt;
Signed-off-by: Benjamin Herrenschmidt &lt;benh@kernel.crashing.org&gt;
Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;

</pre>
</div>
</content>
</entry>
<entry>
<title>powerpc: fix wii_memory_fixups() compile error on 3.0.y tree</title>
<updated>2013-01-21T19:44:59+00:00</updated>
<author>
<name>Shuah Khan</name>
<email>shuah.khan@hp.com</email>
</author>
<published>2012-12-12T23:27:51+00:00</published>
<link rel='alternate' type='text/html' href='https://git.toradex.cn/cgit/linux-toradex.git/commit/?id=e82efee857da0e3331cb57607e0a4058dafadb4b'/>
<id>e82efee857da0e3331cb57607e0a4058dafadb4b</id>
<content type='text'>
[not upstream as the code involved was removed in the 3.3.0 release]

Fix wii_memory_fixups() the following compile error on 3.0.y tree with
wii_defconfig on 3.0.y tree.

  CC      arch/powerpc/platforms/embedded6xx/wii.o
arch/powerpc/platforms/embedded6xx/wii.c: In function ‘wii_memory_fixups’:
arch/powerpc/platforms/embedded6xx/wii.c:88:2: error: format ‘%llx’ expects argument of type ‘long long unsigned int’, but argument 2 has type ‘phys_addr_t’ [-Werror=format]
arch/powerpc/platforms/embedded6xx/wii.c:88:2: error: format ‘%llx’ expects argument of type ‘long long unsigned int’, but argument 3 has type ‘phys_addr_t’ [-Werror=format]
arch/powerpc/platforms/embedded6xx/wii.c:90:2: error: format ‘%llx’ expects argument of type ‘long long unsigned int’, but argument 2 has type ‘phys_addr_t’ [-Werror=format]
arch/powerpc/platforms/embedded6xx/wii.c:90:2: error: format ‘%llx’ expects argument of type ‘long long unsigned int’, but argument 3 has type ‘phys_addr_t’ [-Werror=format]
cc1: all warnings being treated as errors
make[2]: *** [arch/powerpc/platforms/embedded6xx/wii.o] Error 1
make[1]: *** [arch/powerpc/platforms/embedded6xx] Error 2
make: *** [arch/powerpc/platforms] Error 2

Signed-off-by: Shuah Khan &lt;shuah.khan@hp.com&gt;
Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;
</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
[not upstream as the code involved was removed in the 3.3.0 release]

Fix wii_memory_fixups() the following compile error on 3.0.y tree with
wii_defconfig on 3.0.y tree.

  CC      arch/powerpc/platforms/embedded6xx/wii.o
arch/powerpc/platforms/embedded6xx/wii.c: In function ‘wii_memory_fixups’:
arch/powerpc/platforms/embedded6xx/wii.c:88:2: error: format ‘%llx’ expects argument of type ‘long long unsigned int’, but argument 2 has type ‘phys_addr_t’ [-Werror=format]
arch/powerpc/platforms/embedded6xx/wii.c:88:2: error: format ‘%llx’ expects argument of type ‘long long unsigned int’, but argument 3 has type ‘phys_addr_t’ [-Werror=format]
arch/powerpc/platforms/embedded6xx/wii.c:90:2: error: format ‘%llx’ expects argument of type ‘long long unsigned int’, but argument 2 has type ‘phys_addr_t’ [-Werror=format]
arch/powerpc/platforms/embedded6xx/wii.c:90:2: error: format ‘%llx’ expects argument of type ‘long long unsigned int’, but argument 3 has type ‘phys_addr_t’ [-Werror=format]
cc1: all warnings being treated as errors
make[2]: *** [arch/powerpc/platforms/embedded6xx/wii.o] Error 1
make[1]: *** [arch/powerpc/platforms/embedded6xx] Error 2
make: *** [arch/powerpc/platforms] Error 2

Signed-off-by: Shuah Khan &lt;shuah.khan@hp.com&gt;
Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;
</pre>
</div>
</content>
</entry>
<entry>
<title>KVM: PPC: 44x: fix DCR read/write</title>
<updated>2013-01-17T16:44:13+00:00</updated>
<author>
<name>Alexander Graf</name>
<email>agraf@suse.de</email>
</author>
<published>2012-10-06T01:56:35+00:00</published>
<link rel='alternate' type='text/html' href='https://git.toradex.cn/cgit/linux-toradex.git/commit/?id=9d2fdadbde8314c8b55bb4a58af9584897298233'/>
<id>9d2fdadbde8314c8b55bb4a58af9584897298233</id>
<content type='text'>
commit e43a028752fed049e4bd94ef895542f96d79fa74 upstream.

When remembering the direction of a DCR transaction, we should write
to the same variable that we interpret on later when doing vcpu_run
again.

Signed-off-by: Alexander Graf &lt;agraf@suse.de&gt;
Signed-off-by: CAI Qian &lt;caiqian@redhat.com&gt;
Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;

</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
commit e43a028752fed049e4bd94ef895542f96d79fa74 upstream.

When remembering the direction of a DCR transaction, we should write
to the same variable that we interpret on later when doing vcpu_run
again.

Signed-off-by: Alexander Graf &lt;agraf@suse.de&gt;
Signed-off-by: CAI Qian &lt;caiqian@redhat.com&gt;
Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;

</pre>
</div>
</content>
</entry>
<entry>
<title>powerpc/vdso: Remove redundant locking in update_vsyscall_tz()</title>
<updated>2013-01-17T16:43:53+00:00</updated>
<author>
<name>Shan Hai</name>
<email>shan.hai@windriver.com</email>
</author>
<published>2012-11-08T15:57:49+00:00</published>
<link rel='alternate' type='text/html' href='https://git.toradex.cn/cgit/linux-toradex.git/commit/?id=aea63e0027f3eb9ff17fd0b6a4a528d91e9e820f'/>
<id>aea63e0027f3eb9ff17fd0b6a4a528d91e9e820f</id>
<content type='text'>
commit ce73ec6db47af84d1466402781ae0872a9e7873c upstream.

The locking in update_vsyscall_tz() is not only unnecessary because the vdso
code copies the data unproteced in __kernel_gettimeofday() but also
introduces a hard to reproduce race condition between update_vsyscall()
and update_vsyscall_tz(), which causes user space process to loop
forever in vdso code.

The following patch removes the locking from update_vsyscall_tz().

Locking is not only unnecessary because the vdso code copies the data
unprotected in __kernel_gettimeofday() but also erroneous because updating
the tb_update_count is not atomic and introduces a hard to reproduce race
condition between update_vsyscall() and update_vsyscall_tz(), which further
causes user space process to loop forever in vdso code.

The below scenario describes the race condition,
x==0	Boot CPU			other CPU
	proc_P: x==0
	    timer interrupt
		update_vsyscall
x==1		    x++;sync		settimeofday
					    update_vsyscall_tz
x==2						x++;sync
x==3		    sync;x++
						sync;x++
	proc_P: x==3 (loops until x becomes even)

Because the ++ operator would be implemented as three instructions and not
atomic on powerpc.

A similar change was made for x86 in commit 6c260d58634
("x86: vdso: Remove bogus locking in update_vsyscall_tz")

Signed-off-by: Shan Hai &lt;shan.hai@windriver.com&gt;
Signed-off-by: Benjamin Herrenschmidt &lt;benh@kernel.crashing.org&gt;
Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;

</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
commit ce73ec6db47af84d1466402781ae0872a9e7873c upstream.

The locking in update_vsyscall_tz() is not only unnecessary because the vdso
code copies the data unproteced in __kernel_gettimeofday() but also
introduces a hard to reproduce race condition between update_vsyscall()
and update_vsyscall_tz(), which causes user space process to loop
forever in vdso code.

The following patch removes the locking from update_vsyscall_tz().

Locking is not only unnecessary because the vdso code copies the data
unprotected in __kernel_gettimeofday() but also erroneous because updating
the tb_update_count is not atomic and introduces a hard to reproduce race
condition between update_vsyscall() and update_vsyscall_tz(), which further
causes user space process to loop forever in vdso code.

The below scenario describes the race condition,
x==0	Boot CPU			other CPU
	proc_P: x==0
	    timer interrupt
		update_vsyscall
x==1		    x++;sync		settimeofday
					    update_vsyscall_tz
x==2						x++;sync
x==3		    sync;x++
						sync;x++
	proc_P: x==3 (loops until x becomes even)

Because the ++ operator would be implemented as three instructions and not
atomic on powerpc.

A similar change was made for x86 in commit 6c260d58634
("x86: vdso: Remove bogus locking in update_vsyscall_tz")

Signed-off-by: Shan Hai &lt;shan.hai@windriver.com&gt;
Signed-off-by: Benjamin Herrenschmidt &lt;benh@kernel.crashing.org&gt;
Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;

</pre>
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