From b29d31885814003245e2e36373bef4ea6721f114 Mon Sep 17 00:00:00 2001 From: Andrey Konovalov Date: Mon, 20 Nov 2023 18:47:09 +0100 Subject: [PATCH] lib/stackdepot: store free stack records in a freelist Instead of using the global pool_offset variable to find a free slot when storing a new stack record, mainlain a freelist of free slots within the allocated stack pools. A global next_stack variable is used as the head of the freelist, and the next field in the stack_record struct is reused as freelist link (when the record is not in the freelist, this field is used as a link in the hash table). This is preparatory patch for implementing the eviction of stack records from the stack depot. Link: https://lkml.kernel.org/r/b9e4c79955c2121b69301778643b203d3fb09ccc.1700502145.git.andreyknvl@google.com Signed-off-by: Andrey Konovalov Reviewed-by: Alexander Potapenko Cc: Dmitry Vyukov Cc: Evgenii Stepanov Cc: Marco Elver Cc: Oscar Salvador Cc: Vlastimil Babka Signed-off-by: Andrew Morton --- lib/stackdepot.c | 131 +++++++++++++++++++++++++++++------------------ 1 file changed, 82 insertions(+), 49 deletions(-) diff --git a/lib/stackdepot.c b/lib/stackdepot.c index 68c1ac9aa916..a5eff165c0d5 100644 --- a/lib/stackdepot.c +++ b/lib/stackdepot.c @@ -54,8 +54,8 @@ union handle_parts { }; struct stack_record { - struct stack_record *next; /* Link in the hash table */ - u32 hash; /* Hash in the hash table */ + struct stack_record *next; /* Link in hash table or freelist */ + u32 hash; /* Hash in hash table */ u32 size; /* Number of stored frames */ union handle_parts handle; unsigned long entries[CONFIG_STACKDEPOT_MAX_FRAMES]; /* Frames */ @@ -87,10 +87,10 @@ static unsigned int stack_hash_mask; static void *stack_pools[DEPOT_MAX_POOLS]; /* Newly allocated pool that is not yet added to stack_pools. */ static void *new_pool; -/* Currently used pool in stack_pools. */ -static int pool_index; -/* Offset to the unused space in the currently used pool. */ -static size_t pool_offset; +/* Number of pools in stack_pools. */ +static int pools_num; +/* Next stack in the freelist of stack records within stack_pools. */ +static struct stack_record *next_stack; /* Lock that protects the variables above. */ static DEFINE_RAW_SPINLOCK(pool_lock); /* @@ -226,6 +226,42 @@ out_unlock: } EXPORT_SYMBOL_GPL(stack_depot_init); +/* Initializes a stack depol pool. */ +static void depot_init_pool(void *pool) +{ + const int records_in_pool = DEPOT_POOL_SIZE / DEPOT_STACK_RECORD_SIZE; + int i, offset; + + /* Initialize handles and link stack records to each other. */ + for (i = 0, offset = 0; + offset <= DEPOT_POOL_SIZE - DEPOT_STACK_RECORD_SIZE; + i++, offset += DEPOT_STACK_RECORD_SIZE) { + struct stack_record *stack = pool + offset; + + stack->handle.pool_index = pools_num; + stack->handle.offset = offset >> DEPOT_STACK_ALIGN; + stack->handle.extra = 0; + + if (i < records_in_pool - 1) + stack->next = (void *)stack + DEPOT_STACK_RECORD_SIZE; + else + stack->next = NULL; + } + + /* Link stack records into the freelist. */ + WARN_ON(next_stack); + next_stack = pool; + + /* Save reference to the pool to be used by depot_fetch_stack(). */ + stack_pools[pools_num] = pool; + + /* + * WRITE_ONCE() pairs with potential concurrent read in + * depot_fetch_stack(). + */ + WRITE_ONCE(pools_num, pools_num + 1); +} + /* Keeps the preallocated memory to be used for a new stack depot pool. */ static void depot_keep_new_pool(void **prealloc) { @@ -242,7 +278,7 @@ static void depot_keep_new_pool(void **prealloc) * Use the preallocated memory for the new pool * as long as we do not exceed the maximum number of pools. */ - if (pool_index + 1 < DEPOT_MAX_POOLS) { + if (pools_num < DEPOT_MAX_POOLS) { new_pool = *prealloc; *prealloc = NULL; } @@ -258,45 +294,42 @@ static void depot_keep_new_pool(void **prealloc) } /* Updates references to the current and the next stack depot pools. */ -static bool depot_update_pools(size_t required_size, void **prealloc) +static bool depot_update_pools(void **prealloc) { - /* Check if there is not enough space in the current pool. */ - if (unlikely(pool_offset + required_size > DEPOT_POOL_SIZE)) { - /* Bail out if we reached the pool limit. */ - if (unlikely(pool_index + 1 >= DEPOT_MAX_POOLS)) { - WARN_ONCE(1, "Stack depot reached limit capacity"); - return false; - } + /* Check if we still have objects in the freelist. */ + if (next_stack) + goto out_keep_prealloc; - /* - * Move on to the new pool. - * WRITE_ONCE() pairs with potential concurrent read in - * stack_depot_fetch(). - */ - WRITE_ONCE(pool_index, pool_index + 1); - stack_pools[pool_index] = new_pool; + /* Check if we have a new pool saved and use it. */ + if (new_pool) { + depot_init_pool(new_pool); new_pool = NULL; - pool_offset = 0; - /* - * If the maximum number of pools is not reached, take note - * that yet another new pool needs to be allocated. - * smp_store_release() pairs with smp_load_acquire() in - * stack_depot_save(). - */ - if (pool_index + 1 < DEPOT_MAX_POOLS) + /* Take note that we might need a new new_pool. */ + if (pools_num < DEPOT_MAX_POOLS) smp_store_release(&new_pool_required, 1); + + /* Try keeping the preallocated memory for new_pool. */ + goto out_keep_prealloc; } - /* Check if the current pool is not yet allocated. */ - if (*prealloc && stack_pools[pool_index] == NULL) { - /* Use the preallocated memory for the current pool. */ - stack_pools[pool_index] = *prealloc; + /* Bail out if we reached the pool limit. */ + if (unlikely(pools_num >= DEPOT_MAX_POOLS)) { + WARN_ONCE(1, "Stack depot reached limit capacity"); + return false; + } + + /* Check if we have preallocated memory and use it. */ + if (*prealloc) { + depot_init_pool(*prealloc); *prealloc = NULL; return true; } - /* Otherwise, try using the preallocated memory for a new pool. */ + return false; + +out_keep_prealloc: + /* Keep the preallocated memory for a new pool if required. */ if (*prealloc) depot_keep_new_pool(prealloc); return true; @@ -307,35 +340,35 @@ static struct stack_record * depot_alloc_stack(unsigned long *entries, int size, u32 hash, void **prealloc) { struct stack_record *stack; - size_t required_size = DEPOT_STACK_RECORD_SIZE; /* Update current and new pools if required and possible. */ - if (!depot_update_pools(required_size, prealloc)) + if (!depot_update_pools(prealloc)) return NULL; - /* Check if we have a pool to save the stack trace. */ - if (stack_pools[pool_index] == NULL) + /* Check if we have a stack record to save the stack trace. */ + stack = next_stack; + if (!stack) return NULL; + /* Advance the freelist. */ + next_stack = stack->next; + /* Limit number of saved frames to CONFIG_STACKDEPOT_MAX_FRAMES. */ if (size > CONFIG_STACKDEPOT_MAX_FRAMES) size = CONFIG_STACKDEPOT_MAX_FRAMES; /* Save the stack trace. */ - stack = stack_pools[pool_index] + pool_offset; + stack->next = NULL; stack->hash = hash; stack->size = size; - stack->handle.pool_index = pool_index; - stack->handle.offset = pool_offset >> DEPOT_STACK_ALIGN; - stack->handle.extra = 0; + /* stack->handle is already filled in by depot_init_pool(). */ memcpy(stack->entries, entries, flex_array_size(stack, entries, size)); - pool_offset += required_size; /* * Let KMSAN know the stored stack record is initialized. This shall * prevent false positive reports if instrumented code accesses it. */ - kmsan_unpoison_memory(stack, required_size); + kmsan_unpoison_memory(stack, DEPOT_STACK_RECORD_SIZE); return stack; } @@ -345,16 +378,16 @@ static struct stack_record *depot_fetch_stack(depot_stack_handle_t handle) union handle_parts parts = { .handle = handle }; /* * READ_ONCE() pairs with potential concurrent write in - * depot_update_pools(). + * depot_init_pool(). */ - int pool_index_cached = READ_ONCE(pool_index); + int pools_num_cached = READ_ONCE(pools_num); void *pool; size_t offset = parts.offset << DEPOT_STACK_ALIGN; struct stack_record *stack; - if (parts.pool_index > pool_index_cached) { + if (parts.pool_index > pools_num_cached) { WARN(1, "pool index %d out of bounds (%d) for stack id %08x\n", - parts.pool_index, pool_index_cached, handle); + parts.pool_index, pools_num_cached, handle); return NULL; }