staging: lustre: remove page_collection::pc_lock in libcfs

page_collection::pc_lock is supposed to protect race between
functions called by smp_call_function(), however we don't have
this use-case for ages and page_collection only lives in stack
of thread, so it is safe to remove it.
Signed-off-by: Liang Zhen <liang.zhen@intel.com>
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-3055
Reviewed-on: http://review.whamcloud.com/7660Reviewed-by: Bobi Jam <bobijam@gmail.com>
Reviewed-by: Sebastien Buisson <sebastien.buisson@bull.net>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/lustre/lustre/libcfs/tracefile.c

@@ -199,7 +199,6 @@ static void cfs_tcd_shrink(struct cfs_trace_cpu_data *tcd)
 		       pgcount + 1, tcd->tcd_cur_pages);
 
 	INIT_LIST_HEAD(&pc.pc_pages);
-	spin_lock_init(&pc.pc_lock);
 
 	list_for_each_entry_safe(tage, tmp, &tcd->tcd_pages, linkage) {
 		if (pgcount-- == 0)
@@ -522,7 +521,6 @@ static void collect_pages_on_all_cpus(struct page_collection *pc)
 	struct cfs_trace_cpu_data *tcd;
 	int i, cpu;
 
-	spin_lock(&pc->pc_lock);
 	for_each_possible_cpu(cpu) {
 		cfs_tcd_for_each_type_lock(tcd, i, cpu) {
 			list_splice_init(&tcd->tcd_pages, &pc->pc_pages);
@@ -534,7 +532,6 @@ static void collect_pages_on_all_cpus(struct page_collection *pc)
 			}
 		}
 	}
-	spin_unlock(&pc->pc_lock);
 }
 
 static void collect_pages(struct page_collection *pc)
@@ -555,7 +552,6 @@ static void put_pages_back_on_all_cpus(struct page_collection *pc)
 	struct cfs_trace_page *tmp;
 	int i, cpu;
 
-	spin_lock(&pc->pc_lock);
 	for_each_possible_cpu(cpu) {
 		cfs_tcd_for_each_type_lock(tcd, i, cpu) {
 			cur_head = tcd->tcd_pages.next;
@@ -573,7 +569,6 @@ static void put_pages_back_on_all_cpus(struct page_collection *pc)
 			}
 		}
 	}
-	spin_unlock(&pc->pc_lock);
 }
 
 static void put_pages_back(struct page_collection *pc)
@@ -592,7 +587,6 @@ static void put_pages_on_tcd_daemon_list(struct page_collection *pc,
 	struct cfs_trace_page *tage;
 	struct cfs_trace_page *tmp;
 
-	spin_lock(&pc->pc_lock);
 	list_for_each_entry_safe(tage, tmp, &pc->pc_pages, linkage) {
 
 		__LASSERT_TAGE_INVARIANT(tage);
@@ -616,7 +610,6 @@ static void put_pages_on_tcd_daemon_list(struct page_collection *pc,
 			tcd->tcd_cur_daemon_pages--;
 		}
 	}
-	spin_unlock(&pc->pc_lock);
 }
 
 static void put_pages_on_daemon_list(struct page_collection *pc)
@@ -636,8 +629,6 @@ void cfs_trace_debug_print(void)
 	struct cfs_trace_page *tage;
 	struct cfs_trace_page *tmp;
 
-	spin_lock_init(&pc.pc_lock);
-
 	pc.pc_want_daemon_pages = 1;
 	collect_pages(&pc);
 	list_for_each_entry_safe(tage, tmp, &pc.pc_pages, linkage) {
@@ -692,7 +683,6 @@ int cfs_tracefile_dump_all_pages(char *filename)
 		goto out;
 	}
 
-	spin_lock_init(&pc.pc_lock);
 	pc.pc_want_daemon_pages = 1;
 	collect_pages(&pc);
 	if (list_empty(&pc.pc_pages)) {
@@ -739,8 +729,6 @@ void cfs_trace_flush_pages(void)
 	struct cfs_trace_page *tage;
 	struct cfs_trace_page *tmp;
 
-	spin_lock_init(&pc.pc_lock);
-
 	pc.pc_want_daemon_pages = 1;
 	collect_pages(&pc);
 	list_for_each_entry_safe(tage, tmp, &pc.pc_pages, linkage) {
@@ -970,7 +958,6 @@ static int tracefiled(void *arg)
 	/* we're started late enough that we pick up init's fs context */
 	/* this is so broken in uml?  what on earth is going on? */
 
-	spin_lock_init(&pc.pc_lock);
 	complete(&tctl->tctl_start);
 
 	while (1) {
@@ -1170,7 +1157,6 @@ static void cfs_trace_cleanup(void)
 	struct page_collection pc;
 
 	INIT_LIST_HEAD(&pc.pc_pages);
-	spin_lock_init(&pc.pc_lock);
 
 	trace_cleanup_on_all_cpus();
 

drivers/staging/lustre/lustre/libcfs/tracefile.h

@@ -195,14 +195,6 @@ extern union cfs_trace_data_union (*cfs_trace_data[TCD_MAX_TYPES])[NR_CPUS];
  * be moved there */
 struct page_collection {
 	struct list_head	pc_pages;
-	/*
-	 * spin-lock protecting ->pc_pages. It is taken by smp_call_function()
-	 * call-back functions. XXX nikita: Which is horrible: all processors
-	 * receive NMI at the same time only to be serialized by this
-	 * lock. Probably ->pc_pages should be replaced with an array of
-	 * NR_CPUS elements accessed locklessly.
-	 */
-	spinlock_t	pc_lock;
 	/*
 	 * if this flag is set, collect_pages() will spill both
 	 * ->tcd_daemon_pages and ->tcd_pages to the ->pc_pages. Otherwise,