[RFC 04/12] powerpc/pseries: Add context annotations for the DTL worker lock

["Ritesh Harjani (IBM)" <ritesh.list@gmail.com>]

dtl_worker_{enable,disable}() needs annotations since they acquire and
release locks. So this adds conditional annotation based on return value.

Let's also disable context analysis for vcpudispatch_stats_write(),
since based on received input, it can leave the lock held until a later
write of 0 unlocks it. So we need to mark it with __context_unsafe().

Otherwise we get following error on enabling CONTEXT_ANALYSIS on this
file:
  lpar.c:490:9: error: rw_semaphore 'dtl_access_lock' is not held on every path through here [-Werror,-Wthread-safety-analysis]
  lpar.c:498:2: error: releasing rw_semaphore 'dtl_access_lock' that was not held [-Werror,-Wthread-safety-analysis]

Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
---
 arch/powerpc/platforms/pseries/lpar.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/powerpc/platforms/pseries/lpar.c b/arch/powerpc/platforms/pseries/lpar.c
index 5dbf447d3a83..9965ead1e93c 100644
--- a/arch/powerpc/platforms/pseries/lpar.c
+++ b/arch/powerpc/platforms/pseries/lpar.c
@@ -461,6 +461,7 @@ static void reset_global_dtl_mask(void)
 }
 
 static int dtl_worker_enable(unsigned long *time_limit)
+		__cond_acquires(0, &dtl_access_lock)
 {
 	int rc = 0, state;
 
@@ -491,6 +492,7 @@ static int dtl_worker_enable(unsigned long *time_limit)
 }
 
 static void dtl_worker_disable(unsigned long *time_limit)
+		__releases(&dtl_access_lock)
 {
 	cpuhp_remove_state(dtl_worker_state);
 	free_dtl_buffers(time_limit);
@@ -500,6 +502,7 @@ static void dtl_worker_disable(unsigned long *time_limit)
 
 static ssize_t vcpudispatch_stats_write(struct file *file, const char __user *p,
 		size_t count, loff_t *ppos)
+		__context_unsafe(/* dtl_access_lock is held from enable write until disable write */)
 {
 	unsigned long time_limit = jiffies + HZ;
 	struct vcpu_dispatch_data *disp;
-- 
2.39.5