lib/stackdepot: Provide functions which operate on plain storage arrays

The struct stack_trace indirection in the stack depot functions is a truly
pointless excercise which requires horrible code at the callsites.

Provide interfaces based on plain storage arrays.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
Acked-by: Alexander Potapenko <glider@google.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: linux-mm@kvack.org
Cc: David Rientjes <rientjes@google.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: kasan-dev@googlegroups.com
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Akinobu Mita <akinobu.mita@gmail.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: iommu@lists.linux-foundation.org
Cc: Robin Murphy <robin.murphy@arm.com>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: Johannes Thumshirn <jthumshirn@suse.de>
Cc: David Sterba <dsterba@suse.com>
Cc: Chris Mason <clm@fb.com>
Cc: Josef Bacik <josef@toxicpanda.com>
Cc: linux-btrfs@vger.kernel.org
Cc: dm-devel@redhat.com
Cc: Mike Snitzer <snitzer@redhat.com>
Cc: Alasdair Kergon <agk@redhat.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: intel-gfx@lists.freedesktop.org
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: dri-devel@lists.freedesktop.org
Cc: David Airlie <airlied@linux.ie>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Tom Zanussi <tom.zanussi@linux.intel.com>
Cc: Miroslav Benes <mbenes@suse.cz>
Cc: linux-arch@vger.kernel.org
Link: https://lkml.kernel.org/r/20190425094801.414574828@linutronix.de

include/linux/stackdepot.h

@@ -26,7 +26,11 @@ typedef u32 depot_stack_handle_t;
 struct stack_trace;
 
 depot_stack_handle_t depot_save_stack(struct stack_trace *trace, gfp_t flags);
+depot_stack_handle_t stack_depot_save(unsigned long *entries,
+				      unsigned int nr_entries, gfp_t gfp_flags);
 
 void depot_fetch_stack(depot_stack_handle_t handle, struct stack_trace *trace);
+unsigned int stack_depot_fetch(depot_stack_handle_t handle,
+			       unsigned long **entries);
 
 #endif

lib/stackdepot.c

@@ -194,40 +194,60 @@ static inline struct stack_record *find_stack(struct stack_record *bucket,
 	return NULL;
 }
 
-void depot_fetch_stack(depot_stack_handle_t handle, struct stack_trace *trace)
+/**
+ * stack_depot_fetch - Fetch stack entries from a depot
+ *
+ * @handle:		Stack depot handle which was returned from
+ *			stack_depot_save().
+ * @entries:		Pointer to store the entries address
+ *
+ * Return: The number of trace entries for this depot.
+ */
+unsigned int stack_depot_fetch(depot_stack_handle_t handle,
+			       unsigned long **entries)
 {
 	union handle_parts parts = { .handle = handle };
 	void *slab = stack_slabs[parts.slabindex];
 	size_t offset = parts.offset << STACK_ALLOC_ALIGN;
 	struct stack_record *stack = slab + offset;
 
-	trace->nr_entries = trace->max_entries = stack->size;
-	trace->entries = stack->entries;
-	trace->skip = 0;
+	*entries = stack->entries;
+	return stack->size;
+}
+EXPORT_SYMBOL_GPL(stack_depot_fetch);
+
+void depot_fetch_stack(depot_stack_handle_t handle, struct stack_trace *trace)
+{
+	unsigned int nent = stack_depot_fetch(handle, &trace->entries);
+
+	trace->max_entries = trace->nr_entries = nent;
 }
 EXPORT_SYMBOL_GPL(depot_fetch_stack);
 
 /**
- * depot_save_stack - save stack in a stack depot.
- * @trace - the stacktrace to save.
- * @alloc_flags - flags for allocating additional memory if required.
+ * stack_depot_save - Save a stack trace from an array
+ *
+ * @entries:		Pointer to storage array
+ * @nr_entries:		Size of the storage array
+ * @alloc_flags:	Allocation gfp flags
  *
- * Returns the handle of the stack struct stored in depot.
+ * Return: The handle of the stack struct stored in depot
  */
-depot_stack_handle_t depot_save_stack(struct stack_trace *trace,
-				    gfp_t alloc_flags)
+depot_stack_handle_t stack_depot_save(unsigned long *entries,
+				      unsigned int nr_entries,
+				      gfp_t alloc_flags)
 {
-	u32 hash;
-	depot_stack_handle_t retval = 0;
 	struct stack_record *found = NULL, **bucket;
-	unsigned long flags;
+	depot_stack_handle_t retval = 0;
 	struct page *page = NULL;
 	void *prealloc = NULL;
+	unsigned long flags;
+	u32 hash;
 
-	if (unlikely(trace->nr_entries == 0))
+	if (unlikely(nr_entries == 0))
 		goto fast_exit;
 
-	hash = hash_stack(trace->entries, trace->nr_entries);
+	hash = hash_stack(entries, nr_entries);
 	bucket = &stack_table[hash & STACK_HASH_MASK];
 
 	/*
@@ -235,8 +255,8 @@ depot_stack_handle_t depot_save_stack(struct stack_trace *trace,
 	 * The smp_load_acquire() here pairs with smp_store_release() to
 	 * |bucket| below.
 	 */
-	found = find_stack(smp_load_acquire(bucket), trace->entries,
-			   trace->nr_entries, hash);
+	found = find_stack(smp_load_acquire(bucket), entries,
+			   nr_entries, hash);
 	if (found)
 		goto exit;
 
@@ -264,10 +284,10 @@ depot_stack_handle_t depot_save_stack(struct stack_trace *trace,
 
 	spin_lock_irqsave(&depot_lock, flags);
 
-	found = find_stack(*bucket, trace->entries, trace->nr_entries, hash);
+	found = find_stack(*bucket, entries, nr_entries, hash);
 	if (!found) {
 		struct stack_record *new =
-			depot_alloc_stack(trace->entries, trace->nr_entries,
+			depot_alloc_stack(entries, nr_entries,
 					  hash, &prealloc, alloc_flags);
 		if (new) {
 			new->next = *bucket;
@@ -297,4 +317,16 @@ depot_stack_handle_t depot_save_stack(struct stack_trace *trace,
 fast_exit:
 	return retval;
 }
+EXPORT_SYMBOL_GPL(stack_depot_save);
+
+/**
+ * depot_save_stack - save stack in a stack depot.
+ * @trace - the stacktrace to save.
+ * @alloc_flags - flags for allocating additional memory if required.
+ */
+depot_stack_handle_t depot_save_stack(struct stack_trace *trace,
+				      gfp_t alloc_flags)
+{
+	return stack_depot_save(trace->entries, trace->nr_entries, alloc_flags);
+}
 EXPORT_SYMBOL_GPL(depot_save_stack);