• Rob Herring's avatar
    pstore-ram: Fix hangs by using write-combine mappings · 1c5988f8
    Rob Herring authored
    commit 7ae9cb81 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: default avatarKees Cook <keescook@chromium.org>
    Signed-off-by: default avatarRob Herring <rob.herring@calxeda.com>
    [tony@atomide.com: updated description]
    Signed-off-by: default avatarTony Lindgren <tony@atomide.com>
    Signed-off-by: default avatarTony Luck <tony.luck@intel.com>
    Signed-off-by: default avatarJiri Slaby <jslaby@suse.cz>
    1c5988f8
ram_core.c 12.9 KB