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    Subject[PATCH 4.19 074/140] ACPI: OSL: only free map once in osl.c
    Date
    From: Francesco Ruggeri <fruggeri@arista.com>

    commit 833a426cc471b6088011b3d67f1dc4e147614647 upstream.

    acpi_os_map_cleanup checks map->refcount outside of acpi_ioremap_lock
    before freeing the map. This creates a race condition the can result
    in the map being freed more than once.
    A panic can be caused by running

    for ((i=0; i<10; i++))
    do
    for ((j=0; j<100000; j++))
    do
    cat /sys/firmware/acpi/tables/data/BERT >/dev/null
    done &
    done

    This patch makes sure that only the process that drops the reference
    to 0 does the freeing.

    Fixes: b7c1fadd6c2e ("ACPI: Do not use krefs under a mutex in osl.c")
    Signed-off-by: Francesco Ruggeri <fruggeri@arista.com>
    Reviewed-by: Dmitry Safonov <0x7f454c46@gmail.com>
    Cc: All applicable <stable@vger.kernel.org>
    Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/acpi/osl.c | 28 +++++++++++++++++-----------
    1 file changed, 17 insertions(+), 11 deletions(-)

    --- a/drivers/acpi/osl.c
    +++ b/drivers/acpi/osl.c
    @@ -374,19 +374,21 @@ void *__ref acpi_os_map_memory(acpi_phys
    }
    EXPORT_SYMBOL_GPL(acpi_os_map_memory);

    -static void acpi_os_drop_map_ref(struct acpi_ioremap *map)
    +/* Must be called with mutex_lock(&acpi_ioremap_lock) */
    +static unsigned long acpi_os_drop_map_ref(struct acpi_ioremap *map)
    {
    - if (!--map->refcount)
    + unsigned long refcount = --map->refcount;
    +
    + if (!refcount)
    list_del_rcu(&map->list);
    + return refcount;
    }

    static void acpi_os_map_cleanup(struct acpi_ioremap *map)
    {
    - if (!map->refcount) {
    - synchronize_rcu_expedited();
    - acpi_unmap(map->phys, map->virt);
    - kfree(map);
    - }
    + synchronize_rcu_expedited();
    + acpi_unmap(map->phys, map->virt);
    + kfree(map);
    }

    /**
    @@ -406,6 +408,7 @@ static void acpi_os_map_cleanup(struct a
    void __ref acpi_os_unmap_iomem(void __iomem *virt, acpi_size size)
    {
    struct acpi_ioremap *map;
    + unsigned long refcount;

    if (!acpi_permanent_mmap) {
    __acpi_unmap_table(virt, size);
    @@ -419,10 +422,11 @@ void __ref acpi_os_unmap_iomem(void __io
    WARN(true, PREFIX "%s: bad address %p\n", __func__, virt);
    return;
    }
    - acpi_os_drop_map_ref(map);
    + refcount = acpi_os_drop_map_ref(map);
    mutex_unlock(&acpi_ioremap_lock);

    - acpi_os_map_cleanup(map);
    + if (!refcount)
    + acpi_os_map_cleanup(map);
    }
    EXPORT_SYMBOL_GPL(acpi_os_unmap_iomem);

    @@ -457,6 +461,7 @@ void acpi_os_unmap_generic_address(struc
    {
    u64 addr;
    struct acpi_ioremap *map;
    + unsigned long refcount;

    if (gas->space_id != ACPI_ADR_SPACE_SYSTEM_MEMORY)
    return;
    @@ -472,10 +477,11 @@ void acpi_os_unmap_generic_address(struc
    mutex_unlock(&acpi_ioremap_lock);
    return;
    }
    - acpi_os_drop_map_ref(map);
    + refcount = acpi_os_drop_map_ref(map);
    mutex_unlock(&acpi_ioremap_lock);

    - acpi_os_map_cleanup(map);
    + if (!refcount)
    + acpi_os_map_cleanup(map);
    }
    EXPORT_SYMBOL(acpi_os_unmap_generic_address);


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