On 02/26/2016 07:48 PM, Alexander Potapenko wrote:

Stack depot will allow KASAN store allocation/deallocation stack traces
for memory chunks. The stack traces are stored in a hash table and
referenced by handles which reside in the kasan_alloc_meta and
kasan_free_meta structures in the allocated memory chunks.

IRQ stack traces are cut below the IRQ entry point to avoid unnecessary
duplication.

Right now stackdepot support is only enabled in SLAB allocator.
Once KASAN features in SLAB are on par with those in SLUB we can switch
SLUB to stackdepot as well, thus removing the dependency on SLUB stack
bookkeeping, which wastes a lot of memory.

This patch is based on the "mm: kasan: stack depots" patch originally
prepared by Dmitry Chernenkov.

Signed-off-by: Alexander Potapenko <glider@google.com>
---
v2: - per request from Joonsoo Kim, moved the stackdepot implementation to
lib/, as there's a plan to use it for page owner
    - added copyright comments
    - added comments about smp_load_acquire()/smp_store_release()

v3: - minor description changes
---

Just try to imagine that another subsystem wants to use stackdepot. How this gonna look like?

We have Kconfig to describe dependencies. So, this should be under CONFIG_STACKDEPOT.
So any user of this feature can just do 'select STACKDEPOT' in Kconfig.

+/* Allocation of a new stack in raw storage */
+static struct stack_record *depot_alloc_stack(unsigned long *entries, int size,
+		u32 hash, void **prealloc, gfp_t alloc_flags)
+{

+
+	stack->hash = hash;
+	stack->size = size;
+	stack->handle.slabindex = depot_index;
+	stack->handle.offset = depot_offset >> STACK_ALLOC_ALIGN;
+	__memcpy(stack->entries, entries, size * sizeof(unsigned long));

s/__memcpy/memcpy

+	depot_offset += required_size;
+
+	return stack;
+}
+

+/*
+ * depot_save_stack - save stack in a stack depot.
+ * @trace - the stacktrace to save.
+ * @alloc_flags - flags for allocating additional memory if required.
+ *
+ * Returns the handle of the stack struct stored in depot.
+ */
+depot_stack_handle depot_save_stack(struct stack_trace *trace,
+				    gfp_t alloc_flags)
+{
+	u32 hash;
+	depot_stack_handle retval = 0;
+	struct stack_record *found = NULL, **bucket;
+	unsigned long flags;
+	struct page *page = NULL;
+	void *prealloc = NULL;
+
+	if (unlikely(trace->nr_entries == 0))
+		goto exit;
+
+	hash = hash_stack(trace->entries, trace->nr_entries);
+	/* Bad luck, we won't store this stack. */
+	if (hash == 0)
+		goto exit;
+
+	bucket = &stack_table[hash & STACK_HASH_MASK];
+
+	/* Fast path: look the stack trace up without locking.
+	 *
+	 * 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);
+	if (found)
+		goto exit;
+
+	/* Check if the current or the next stack slab need to be initialized.
+	 * If so, allocate the memory - we won't be able to do that under the
+	 * lock.
+	 *
+	 * The smp_load_acquire() here pairs with smp_store_release() to
+	 * |next_slab_inited| in depot_alloc_stack() and init_stack_slab().
+	 */
+	if (unlikely(!smp_load_acquire(&next_slab_inited))) {
+		if (!preempt_count() && !in_irq()) {

If you trying to detect atomic context here, than this doesn't work. E.g. you can't know
about held spinlocks in non-preemptible kernel.
And I'm not sure why need this. You know gfp flags here, so allocation in atomic context shouldn't be problem.

+			alloc_flags &= (__GFP_RECLAIM | __GFP_IO | __GFP_FS |
+				__GFP_NOWARN | __GFP_NORETRY |
+				__GFP_NOMEMALLOC | __GFP_DIRECT_RECLAIM);

I think blacklist approach would be better here.

+			page = alloc_pages(alloc_flags, STACK_ALLOC_ORDER);

STACK_ALLOC_ORDER = 4 - that's a lot. Do you really need that much?

Extra newline.

I think, you can reduce this (32 perhaps?). Kernel stacks are not so deep usually.

+
 struct kasan_track {
 	u64 cpu : 6;			/* for NR_CPUS = 64 */
 	u64 pid : 16;			/* 65536 processes */
 	u64 when : 42;			/* ~140 years */
+	depot_stack_handle stack : sizeof(depot_stack_handle);
 };