On 01/23/2017 09:30 AM, Oleg Nesterov wrote:
Hello,
smp_mb__after_atomic() looks wrong and misleading, sock_reset_flag() does the
non-atomic __clear_bit() and thus it can not guarantee test_bit(SOCK_NOSPACE)
(non-atomic too) won't be reordered.
Indeed. Here's a bit of discussion on it:
http://marc.info/?l=linux-netdev&m=146662325920596&w=2
It was added by 3c7151275c0c9a "tcp: add memory barriers to write space paths"
and the patch looks correct in that we need the barriers in tcp_check_space()
and tcp_poll() in theory, so it seems tcp_check_space() needs smp_mb() ?
Yes, I think it should be upgraded to an smp_mb() there. If you agree
with this analysis, I will send a patch to upgrade it. Note, I did not
actually run into this race in practice.
Thanks,
-Jason
