From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Arnd Bergmann , Anton Vorontsov , Colin Cross , Olof Johansson , Kees Cook , Rob Herring , Tony Lindgren , Tony Luck Subject: [PATCH 3.10 12/44] pstore-ram: Fix hangs by using write-combine mappings Date: Tue, 13 Jan 2015 23:23:33 -0800 Message-Id: <20150114072228.180973750@linuxfoundation.org> In-Reply-To: <20150114072227.419663002@linuxfoundation.org> References: <20150114072227.419663002@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15 Sender: linux-kernel-owner@vger.kernel.org List-ID: 3.10-stable review patch. If anyone has any objections, please let me know. ------------------ From: Rob Herring 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 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 Cc: Anton Vorontsov Cc: Colin Cross Cc: Olof Johansson Cc: linux-kernel@vger.kernel.org Acked-by: Kees Cook Signed-off-by: Rob Herring [tony@atomide.com: updated description] Signed-off-by: Tony Lindgren Signed-off-by: Tony Luck Signed-off-by: Greg Kroah-Hartman --- 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,