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    SubjectRe: [PATCH v8 6/7] apei/ghes: Use unrcu_pointer for cmpxchg
    On Tue, Oct 11, 2022 at 02:32:48PM +0000, Justin He wrote:
    > My original purpose is to make it pass the sparse checking.

    Then do this pls.

    This is a combined diff - do a second patch which does only remove the
    smp_wmb(). The smp_wmb() there is not needed as the cmpxchg() already
    implies a smp_mb() so there's no need for that separate, explicit one.

    But it would be prudent to have it in a separate patch just in case.

    Thx.

    ---
    diff --git a/drivers/acpi/apei/ghes.c b/drivers/acpi/apei/ghes.c
    index 85acfc589fb7..fd285bf8d114 100644
    --- a/drivers/acpi/apei/ghes.c
    +++ b/drivers/acpi/apei/ghes.c
    @@ -154,7 +154,7 @@ struct ghes_vendor_record_entry {
    static struct gen_pool *ghes_estatus_pool;
    static unsigned long ghes_estatus_pool_size_request;

    -static struct ghes_estatus_cache *ghes_estatus_caches[GHES_ESTATUS_CACHES_SIZE];
    +static struct ghes_estatus_cache __rcu *ghes_estatus_caches[GHES_ESTATUS_CACHES_SIZE];
    static atomic_t ghes_estatus_cache_alloced;

    static int ghes_panic_timeout __read_mostly = 30;
    @@ -842,9 +842,7 @@ static void ghes_estatus_cache_add(
    slot_cache = cache;
    }
    }
    - /* new_cache must be put into array after its contents are written */
    - smp_wmb();
    - if (slot != -1 && cmpxchg(ghes_estatus_caches + slot,
    + if (slot != -1 && cmpxchg((struct ghes_estatus_cache ** __force)(ghes_estatus_caches + slot),
    slot_cache, new_cache) == slot_cache) {
    if (slot_cache)
    call_rcu(&slot_cache->rcu, ghes_estatus_cache_rcu_free);
    --
    Regards/Gruss,
    Boris.

    https://people.kernel.org/tglx/notes-about-netiquette

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