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Subject[PATCH 02/43] stackdepot: reserve 5 extra bits in depot_stack_handle_t
From
Some users (currently only KMSAN) may want to use spare bits in
depot_stack_handle_t. Let them do so by adding @extra_bits to
__stack_depot_save() to store arbitrary flags, and providing
stack_depot_get_extra_bits() to retrieve those flags.

Signed-off-by: Alexander Potapenko <glider@google.com>
---
Link: https://linux-review.googlesource.com/id/I0587f6c777667864768daf07821d594bce6d8ff9
---
include/linux/stackdepot.h | 8 ++++++++
lib/stackdepot.c | 29 ++++++++++++++++++++++++-----
2 files changed, 32 insertions(+), 5 deletions(-)

diff --git a/include/linux/stackdepot.h b/include/linux/stackdepot.h
index c34b55a6e5540..b24f404ab03ac 100644
--- a/include/linux/stackdepot.h
+++ b/include/linux/stackdepot.h
@@ -14,9 +14,15 @@
#include <linux/gfp.h>

typedef u32 depot_stack_handle_t;
+/*
+ * Number of bits in the handle that stack depot doesn't use. Users may store
+ * information in them.
+ */
+#define STACK_DEPOT_EXTRA_BITS 5

depot_stack_handle_t __stack_depot_save(unsigned long *entries,
unsigned int nr_entries,
+ unsigned int extra_bits,
gfp_t gfp_flags, bool can_alloc);

depot_stack_handle_t stack_depot_save(unsigned long *entries,
@@ -25,6 +31,8 @@ depot_stack_handle_t stack_depot_save(unsigned long *entries,
unsigned int stack_depot_fetch(depot_stack_handle_t handle,
unsigned long **entries);

+unsigned int stack_depot_get_extra_bits(depot_stack_handle_t handle);
+
int stack_depot_snprint(depot_stack_handle_t handle, char *buf, size_t size,
int spaces);

diff --git a/lib/stackdepot.c b/lib/stackdepot.c
index b437ae79aca14..6ad7b8888ff19 100644
--- a/lib/stackdepot.c
+++ b/lib/stackdepot.c
@@ -41,7 +41,8 @@
#define STACK_ALLOC_OFFSET_BITS (STACK_ALLOC_ORDER + PAGE_SHIFT - \
STACK_ALLOC_ALIGN)
#define STACK_ALLOC_INDEX_BITS (DEPOT_STACK_BITS - \
- STACK_ALLOC_NULL_PROTECTION_BITS - STACK_ALLOC_OFFSET_BITS)
+ STACK_ALLOC_NULL_PROTECTION_BITS - \
+ STACK_ALLOC_OFFSET_BITS - STACK_DEPOT_EXTRA_BITS)
#define STACK_ALLOC_SLABS_CAP 8192
#define STACK_ALLOC_MAX_SLABS \
(((1LL << (STACK_ALLOC_INDEX_BITS)) < STACK_ALLOC_SLABS_CAP) ? \
@@ -54,6 +55,7 @@ union handle_parts {
u32 slabindex : STACK_ALLOC_INDEX_BITS;
u32 offset : STACK_ALLOC_OFFSET_BITS;
u32 valid : STACK_ALLOC_NULL_PROTECTION_BITS;
+ u32 extra : STACK_DEPOT_EXTRA_BITS;
};
};

@@ -72,6 +74,14 @@ static int next_slab_inited;
static size_t depot_offset;
static DEFINE_RAW_SPINLOCK(depot_lock);

+unsigned int stack_depot_get_extra_bits(depot_stack_handle_t handle)
+{
+ union handle_parts parts = { .handle = handle };
+
+ return parts.extra;
+}
+EXPORT_SYMBOL(stack_depot_get_extra_bits);
+
static bool init_stack_slab(void **prealloc)
{
if (!*prealloc)
@@ -135,6 +145,7 @@ depot_alloc_stack(unsigned long *entries, int size, u32 hash, void **prealloc)
stack->handle.slabindex = depot_index;
stack->handle.offset = depot_offset >> STACK_ALLOC_ALIGN;
stack->handle.valid = 1;
+ stack->handle.extra = 0;
memcpy(stack->entries, entries, flex_array_size(stack, entries, size));
depot_offset += required_size;

@@ -297,6 +308,7 @@ EXPORT_SYMBOL_GPL(stack_depot_fetch);
*
* @entries: Pointer to storage array
* @nr_entries: Size of the storage array
+ * @extra_bits: Flags to store in unused bits of depot_stack_handle_t
* @alloc_flags: Allocation gfp flags
* @can_alloc: Allocate stack slabs (increased chance of failure if false)
*
@@ -305,6 +317,10 @@ EXPORT_SYMBOL_GPL(stack_depot_fetch);
* (allocates using GFP flags of @alloc_flags). If @can_alloc is %false, avoids
* any allocations and will fail if no space is left to store the stack trace.
*
+ * Additional opaque flags can be passed in @extra_bits, stored in the unused
+ * bits of the stack handle, and retrieved using stack_depot_get_extra_bits()
+ * without calling stack_depot_fetch().
+ *
* Context: Any context, but setting @can_alloc to %false is required if
* alloc_pages() cannot be used from the current context. Currently
* this is the case from contexts where neither %GFP_ATOMIC nor
@@ -314,10 +330,11 @@ EXPORT_SYMBOL_GPL(stack_depot_fetch);
*/
depot_stack_handle_t __stack_depot_save(unsigned long *entries,
unsigned int nr_entries,
+ unsigned int extra_bits,
gfp_t alloc_flags, bool can_alloc)
{
struct stack_record *found = NULL, **bucket;
- depot_stack_handle_t retval = 0;
+ union handle_parts retval = { .handle = 0 };
struct page *page = NULL;
void *prealloc = NULL;
unsigned long flags;
@@ -391,9 +408,11 @@ depot_stack_handle_t __stack_depot_save(unsigned long *entries,
free_pages((unsigned long)prealloc, STACK_ALLOC_ORDER);
}
if (found)
- retval = found->handle.handle;
+ retval.handle = found->handle.handle;
fast_exit:
- return retval;
+ retval.extra = extra_bits;
+
+ return retval.handle;
}
EXPORT_SYMBOL_GPL(__stack_depot_save);

@@ -413,6 +432,6 @@ depot_stack_handle_t stack_depot_save(unsigned long *entries,
unsigned int nr_entries,
gfp_t alloc_flags)
{
- return __stack_depot_save(entries, nr_entries, alloc_flags, true);
+ return __stack_depot_save(entries, nr_entries, 0, alloc_flags, true);
}
EXPORT_SYMBOL_GPL(stack_depot_save);
--
2.34.1.173.g76aa8bc2d0-goog
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