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    Subject[PATCH 3.10 12/44] pstore-ram: Fix hangs by using write-combine mappings
    Date
    3.10-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Rob Herring <robherring2@gmail.com>

    commit 7ae9cb81933515dc7db1aa3c47ef7653717e3090 upstream.

    Currently trying to use pstore on at least ARMs can hang as we're
    mapping the peristent RAM with pgprot_noncached().

    On ARMs, pgprot_noncached() will actually make the memory strongly
    ordered, and as the atomic operations pstore uses are implementation
    defined for strongly ordered memory, they may not work. So basically
    atomic operations have undefined behavior on ARM for device or strongly
    ordered memory types.

    Let's fix the issue by using write-combine variants for mappings. This
    corresponds to normal, non-cacheable memory on ARM. For many other
    architectures, this change does not change the mapping type as by
    default we have:

    #define pgprot_writecombine pgprot_noncached

    The reason why pgprot_noncached() was originaly used for pstore
    is because Colin Cross <ccross@android.com> had observed lost
    debug prints right before a device hanging write operation on some
    systems. For the platforms supporting pgprot_noncached(), we can
    add a an optional configuration option to support that. But let's
    get pstore working first before adding new features.

    Cc: Arnd Bergmann <arnd@arndb.de>
    Cc: Anton Vorontsov <cbouatmailru@gmail.com>
    Cc: Colin Cross <ccross@android.com>
    Cc: Olof Johansson <olof@lixom.net>
    Cc: linux-kernel@vger.kernel.org
    Acked-by: Kees Cook <keescook@chromium.org>
    Signed-off-by: Rob Herring <rob.herring@calxeda.com>
    [tony@atomide.com: updated description]
    Signed-off-by: Tony Lindgren <tony@atomide.com>
    Signed-off-by: Tony Luck <tony.luck@intel.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    fs/pstore/ram_core.c | 4 ++--
    1 file changed, 2 insertions(+), 2 deletions(-)

    --- a/fs/pstore/ram_core.c
    +++ b/fs/pstore/ram_core.c
    @@ -345,7 +345,7 @@ static void *persistent_ram_vmap(phys_ad
    page_start = start - offset_in_page(start);
    page_count = DIV_ROUND_UP(size + offset_in_page(start), PAGE_SIZE);

    - prot = pgprot_noncached(PAGE_KERNEL);
    + prot = pgprot_writecombine(PAGE_KERNEL);

    pages = kmalloc(sizeof(struct page *) * page_count, GFP_KERNEL);
    if (!pages) {
    @@ -372,7 +372,7 @@ static void *persistent_ram_iomap(phys_a
    return NULL;
    }

    - return ioremap(start, size);
    + return ioremap_wc(start, size);
    }

    static int persistent_ram_buffer_map(phys_addr_t start, phys_addr_t size,



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