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    Subject[PATCH 06/15] stackdepot: fix and clean-up atomic annotations
    Date
    From: Andrey Konovalov <andreyknvl@google.com>

    Simplify comments accompanying the use of atomic accesses in the
    stack depot code.

    Also turn smp_load_acquire from next_pool_required in depot_init_pool
    into READ_ONCE, as both depot_init_pool and the all smp_store_release's
    to this variable are executed under the stack depot lock.

    Signed-off-by: Andrey Konovalov <andreyknvl@google.com>

    ---

    This patch is not strictly required, as the atomic accesses are fully
    removed in one of the latter patches. However, I decided to keep the
    patch just in case we end up needing these atomics in the following
    iterations of this series.
    ---
    lib/stackdepot.c | 27 +++++++++++++--------------
    1 file changed, 13 insertions(+), 14 deletions(-)

    diff --git a/lib/stackdepot.c b/lib/stackdepot.c
    index 93191ee70fc3..9ae71e1ef1a7 100644
    --- a/lib/stackdepot.c
    +++ b/lib/stackdepot.c
    @@ -226,10 +226,10 @@ static void depot_init_pool(void **prealloc)
    /*
    * If the next pool is already initialized or the maximum number of
    * pools is reached, do not use the preallocated memory.
    - * smp_load_acquire() here pairs with smp_store_release() below and
    - * in depot_alloc_stack().
    + * READ_ONCE is only used to mark the variable as atomic,
    + * there are no concurrent writes.
    */
    - if (!smp_load_acquire(&next_pool_required))
    + if (!READ_ONCE(next_pool_required))
    return;

    /* Check if the current pool is not yet allocated. */
    @@ -250,8 +250,8 @@ static void depot_init_pool(void **prealloc)
    * At this point, either the next pool is initialized or the
    * maximum number of pools is reached. In either case, take
    * note that initializing another pool is not required.
    - * This smp_store_release pairs with smp_load_acquire() above
    - * and in stack_depot_save().
    + * smp_store_release pairs with smp_load_acquire in
    + * stack_depot_save.
    */
    smp_store_release(&next_pool_required, 0);
    }
    @@ -275,15 +275,15 @@ depot_alloc_stack(unsigned long *entries, int size, u32 hash, void **prealloc)
    /*
    * Move on to the next pool.
    * WRITE_ONCE pairs with potential concurrent read in
    - * stack_depot_fetch().
    + * stack_depot_fetch.
    */
    WRITE_ONCE(pool_index, pool_index + 1);
    pool_offset = 0;
    /*
    * If the maximum number of pools is not reached, take note
    * that the next pool needs to initialized.
    - * smp_store_release() here pairs with smp_load_acquire() in
    - * stack_depot_save() and depot_init_pool().
    + * smp_store_release pairs with smp_load_acquire in
    + * stack_depot_save.
    */
    if (pool_index + 1 < DEPOT_MAX_POOLS)
    smp_store_release(&next_pool_required, 1);
    @@ -414,8 +414,7 @@ depot_stack_handle_t __stack_depot_save(unsigned long *entries,

    /*
    * Fast path: look the stack trace up without locking.
    - * The smp_load_acquire() here pairs with smp_store_release() to
    - * |bucket| below.
    + * smp_load_acquire pairs with smp_store_release to |bucket| below.
    */
    found = find_stack(smp_load_acquire(bucket), entries, nr_entries, hash);
    if (found)
    @@ -425,8 +424,8 @@ depot_stack_handle_t __stack_depot_save(unsigned long *entries,
    * Check if another stack pool needs to be initialized. If so, allocate
    * the memory now - we won't be able to do that under the lock.
    *
    - * The smp_load_acquire() here pairs with smp_store_release() to
    - * |next_pool_inited| in depot_alloc_stack() and depot_init_pool().
    + * smp_load_acquire pairs with smp_store_release
    + * in depot_alloc_stack and depot_init_pool.
    */
    if (unlikely(can_alloc && smp_load_acquire(&next_pool_required))) {
    /*
    @@ -452,8 +451,8 @@ depot_stack_handle_t __stack_depot_save(unsigned long *entries,
    if (new) {
    new->next = *bucket;
    /*
    - * This smp_store_release() pairs with
    - * smp_load_acquire() from |bucket| above.
    + * smp_store_release pairs with smp_load_acquire
    + * from |bucket| above.
    */
    smp_store_release(bucket, new);
    found = new;
    --
    2.25.1
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