linux-toradex.git/arch/powerpc/lib/locks.c, branch v5.0

powerpc: clean the inclusion of stringify.h

2018-07-30T12:48:17+00:00

Only include linux/stringify.h is files using __stringify()

Signed-off-by: Christophe Leroy 
Signed-off-by: Michael Ellerman

powerpc/spinlock: Fix spin_unlock_wait()

2016-06-14T06:05:44+00:00

There is an ordering issue with spin_unlock_wait() on powerpc, because
the spin_lock primitive is an ACQUIRE and an ACQUIRE is only ordering
the load part of the operation with memory operations following it.
Therefore the following event sequence can happen:

CPU 1			CPU 2			CPU 3

==================	====================	==============
						spin_unlock(&lock);
			spin_lock(&lock):
			  r1 = *lock; // r1 == 0;
o = object;		o = READ_ONCE(object); // reordered here
object = NULL;
smp_mb();
spin_unlock_wait(&lock);
			  *lock = 1;
smp_mb();
o->dead = true;         < o = READ_ONCE(object); > // reordered upwards
			if (o) // true
				BUG_ON(o->dead); // true!!

To fix this, we add a "nop" ll/sc loop in arch_spin_unlock_wait() on
ppc, the "nop" ll/sc loop reads the lock
value and writes it back atomically, in this way it will synchronize the
view of the lock on CPU1 with that on CPU2. Therefore in the scenario
above, either CPU2 will fail to get the lock at first or CPU1 will see
the lock acquired by CPU2, both cases will eliminate this bug. This is a
similar idea as what Will Deacon did for ARM64 in:

  d86b8da04dfa ("arm64: spinlock: serialise spin_unlock_wait against concurrent lockers")

Furthermore, if the "nop" ll/sc figures out the lock is locked, we
actually don't need to do the "nop" ll/sc trick again, we can just do a
normal load+check loop for the lock to be released, because in that
case, spin_unlock_wait() is called when someone is holding the lock, and
the store part of the "nop" ll/sc happens before the lock release of the
current lock holder:

	"nop" ll/sc -> spin_unlock()

and the lock release happens before the next lock acquisition:

	spin_unlock() -> spin_lock() 

which means the "nop" ll/sc happens before the next lock acquisition:

	"nop" ll/sc -> spin_unlock() -> spin_lock() 

With a smp_mb() preceding spin_unlock_wait(), the store of object is
guaranteed to be observed by the next lock holder:

	STORE -> smp_mb() -> "nop" ll/sc
	-> spin_unlock() -> spin_lock() 

This patch therefore fixes the issue and also cleans the
arch_spin_unlock_wait() a little bit by removing superfluous memory
barriers in loops and consolidating the implementations for PPC32 and
PPC64 into one.

Suggested-by: "Paul E. McKenney" 
Signed-off-by: Boqun Feng 
Reviewed-by: "Paul E. McKenney" 
[mpe: Inline the "nop" ll/sc loop and set EH=0, munge change log]
Signed-off-by: Michael Ellerman

cpufreq/ppc: Add missing #include

2015-03-25T05:53:28+00:00

If CONFIG_SMP=n,  does not include , causing:

drivers/cpufreq/ppc-corenet-cpufreq.c: In function 'corenet_cpufreq_cpu_init':
drivers/cpufreq/ppc-corenet-cpufreq.c:173:3: error: implicit declaration of function 'get_hard_smp_processor_id' [-Werror=implicit-funcuresh E. Warrier" 
X-Patchwork-Id: 443703
Message-Id: <54EE5989.7010800@linux.vnet.ibm.com>
To: linuxppc-dev@ozlabs.org
Date: Wed, 25 Feb 2015 17:23:53 -0600

Export __spin_yield so that the arch_spin_unlock() function can
be invoked from a module. This will be required for modules where
we want to take a lock that is also is acquired in hypervisor
real mode. Because we want to avoid running any lockdep code
(which may not be safe in real mode), this lock needs to be
an arch_spinlock_t instead of a normal spinlock.

Signed-off-by: Suresh Warrier 
Acked-by: Paul Mackerras 
Signed-off-by: Benjamin Herrenschmidt

powerpc: Add smp_mb()s to arch_spin_unlock_wait()

2014-08-13T05:13:27+00:00

Similar to the previous commit which described why we need to add a
barrier to arch_spin_is_locked(), we have a similar problem with
spin_unlock_wait().

We need a barrier on entry to ensure any spinlock we have previously
taken is visibly locked prior to the load of lock->slock.

It's also not clear if spin_unlock_wait() is intended to have ACQUIRE
semantics. For now be conservative and add a barrier on exit to give it
ACQUIRE semantics.

Signed-off-by: Michael Ellerman 
Signed-off-by: Benjamin Herrenschmidt

powerpc: Fix little endian lppaca, slb_shadow and dtl_entry

2013-08-14T05:33:35+00:00

The lppaca, slb_shadow and dtl_entry hypervisor structures are
big endian, so we have to byte swap them in little endian builds.

LE KVM hosts will also need to be fixed but for now add an #error
to remind us.

Signed-off-by: Anton Blanchard 
Signed-off-by: Benjamin Herrenschmidt

powerpc: Remove FW_FEATURE ISERIES from arch code

2012-03-21T00:16:11+00:00

This is no longer selectable, so just remove all the dependent code.

Signed-off-by: Stephen Rothwell 
Signed-off-by: Benjamin Herrenschmidt

powerpc: various straight conversions from module.h --> export.h

2011-10-31T23:30:44+00:00

All these files were including module.h just for the basic
EXPORT_SYMBOL infrastructure.  We can shift them off to the
export.h header which is a way smaller footprint and thus
realize some compile time gains.

Signed-off-by: Paul Gortmaker

powerpc: Abstract indexing of lppaca structs

2010-09-02T04:07:31+00:00

Currently we have the lppaca structs as a simple array of NR_CPUS
entries, taking up space in the data section of the kernel image.
In future we would like to allocate them dynamically, so this
abstracts out the accesses to the array, making it easier to
change how we locate the lppaca for a given cpu in future.
Specifically, lppaca[cpu] changes to lppaca_of(cpu).

Signed-off-by: Paul Mackerras 
Signed-off-by: Benjamin Herrenschmidt

locking: Convert raw_rwlock to arch_rwlock

2009-12-14T22:55:32+00:00

Not strictly necessary for -rt as -rt does not have non sleeping
rwlocks, but it's odd to not have a consistent naming convention.

No functional change.

Signed-off-by: Thomas Gleixner 
Acked-by: Peter Zijlstra 
Acked-by: David S. Miller 
Acked-by: Ingo Molnar 
Cc: linux-arch@vger.kernel.org

locking: Convert __raw_spin* functions to arch_spin*

2009-12-14T22:55:32+00:00

Name space cleanup. No functional change.

Signed-off-by: Thomas Gleixner 
Acked-by: Peter Zijlstra 
Acked-by: David S. Miller 
Acked-by: Ingo Molnar 
Cc: linux-arch@vger.kernel.org