Hi Arnd, On Sat, Dec 10, 2016 at 11:36:34AM +0100, Arnd Bergmann wrote: > A change to the netfilter code in net-next introduced the first caller of > cmpxchg64 that can get built on ARMv7-M, leading to an error from the > assembler that points out the lack of 64-bit atomics on this architecture: > > /tmp/ccMe7djj.s: Assembler messages: > /tmp/ccMe7djj.s:367: Error: selected processor does not support `ldrexd r0,r1,[lr]' in Thumb mode > /tmp/ccMe7djj.s:371: Error: selected processor does not support `strexd ip,r2,r3,[lr]' in Thumb mode > /tmp/ccMe7djj.s:389: Error: selected processor does not support `ldrexd r8,r9,[r7]' in Thumb mode > /tmp/ccMe7djj.s:393: Error: selected processor does not support `strexd lr,r0,r1,[r7]' in Thumb mode > scripts/Makefile.build:299: recipe for target 'net/netfilter/nft_counter.o' failed > > This makes ARMv7-M use the same emulation from asm-generic/cmpxchg-local.h > that we use on architectures earlier than ARMv6K, to fix the build. The > 32-bit atomics are available on ARMv7-M and we keep using them there. > This ARM specific change is probably something we should do regardless > of the netfilter code. > > However, looking at the new nft_counter_reset() function in nft_counter.c, > this looks incorrect to me not just on ARMv7-M but also on other > architectures, with at least the following possible race: Right, Eric Dumazet already spotted this problem. I'm preparing a patch that doesn't require cmpxchg64(). Will keep you on Cc. Thanks. -- To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
