stackdepot: rename pool_index to pool_index_plus_1

Commit 3ee34eabac2a ("lib/stackdepot: fix first entry having a 0-handle")
changed the meaning of the pool_index field to mean "the pool index plus
1".  This made the code accessing this field less self-documenting, as
well as causing debuggers such as drgn to not be able to easily remain
compatible with both old and new kernels, because they typically do that
by testing for presence of the new field.  Because stackdepot is a
debugging tool, we should make sure that it is debugger friendly.
Therefore, give the field a different name to improve readability as well
as enabling debugger backwards compatibility.

This is needed in 6.9, which would otherwise become an odd release with
the new semantics and old name so debuggers wouldn't recognize the new
semantics there.

Fixes: 3ee34eabac2a ("lib/stackdepot: fix first entry having a 0-handle")
Link: https://lkml.kernel.org/r/20240402001500.53533-1-pcc@google.com
Link: https://linux-review.googlesource.com/id/Ib3e70c36c1d230dd0a118dc22649b33e768b9f88
Signed-off-by: Peter Collingbourne <pcc@google.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Alexander Potapenko <glider@google.com>
Acked-by: Marco Elver <elver@google.com>
Acked-by: Oscar Salvador <osalvador@suse.de>
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Omar Sandoval <osandov@fb.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/include/linux/stackdepot.h b/include/linux/stackdepot.h
index 3c6caa5abc7c4262b8d62f9ef46d3fa273e7fb1e..e9ec32fb97d4a729e06aaabc7cd5627bb384d72f 100644 (file)
--- a/include/linux/stackdepot.h
+++ b/include/linux/stackdepot.h
@@ -44,10 +44,9 @@ typedef u32 depot_stack_handle_t;
 union handle_parts {
        depot_stack_handle_t handle;
        struct {
-               /* pool_index is offset by 1 */
-               u32 pool_index  : DEPOT_POOL_INDEX_BITS;
-               u32 offset      : DEPOT_OFFSET_BITS;
-               u32 extra       : STACK_DEPOT_EXTRA_BITS;
+               u32 pool_index_plus_1   : DEPOT_POOL_INDEX_BITS;
+               u32 offset              : DEPOT_OFFSET_BITS;
+               u32 extra               : STACK_DEPOT_EXTRA_BITS;
        };
 };
 

diff --git a/lib/stackdepot.c b/lib/stackdepot.c
index af6cc19a200331aa0c37cf2e497384f0b19d8db0..68c97387aa54e2728b79b2cacf23815fcb2f90ca 100644 (file)
--- a/lib/stackdepot.c
+++ b/lib/stackdepot.c
@@ -330,7 +330,7 @@ static struct stack_record *depot_pop_free_pool(void **prealloc, size_t size)
        stack = current_pool + pool_offset;
 
        /* Pre-initialize handle once. */
-       stack->handle.pool_index = pool_index + 1;
+       stack->handle.pool_index_plus_1 = pool_index + 1;
        stack->handle.offset = pool_offset >> DEPOT_STACK_ALIGN;
        stack->handle.extra = 0;
        INIT_LIST_HEAD(&stack->hash_list);
@@ -441,7 +441,7 @@ static struct stack_record *depot_fetch_stack(depot_stack_handle_t handle)
        const int pools_num_cached = READ_ONCE(pools_num);
        union handle_parts parts = { .handle = handle };
        void *pool;
-       u32 pool_index = parts.pool_index - 1;
+       u32 pool_index = parts.pool_index_plus_1 - 1;
        size_t offset = parts.offset << DEPOT_STACK_ALIGN;
        struct stack_record *stack;