On Tue, Oct 11, 2016 at 09:20:17AM +0200, Julien Charbon wrote: > Then threads are competing for the INP_WLOCK lock. For the example, > let's say the thread A wants to run tcp_input()/in_pcblookup_mbuf() and > racing for this INP_WLOCK: > > https://github.com/freebsd/freebsd/blob/release/11.0.0/sys/netinet/in_pcb.c#L1964 > > And thread B wants to run tcp_timer_2msl()/tcp_close()/in_pcbdrop() and > racing for this INP_WLOCK: > > https://github.com/freebsd/freebsd/blob/release/11.0.0/sys/netinet/tcp_timer.c#L323 > > That leads to two cases: > > o Thread A wins the race: > > Thread A will continue tcp_input() as usal and INP_DROPPED flags is > not set and inp is still in TCP hash table. > Thread B is waiting on thread A to release INP_WLOCK after finishing > tcp_input() processing, and thread B will continue > tcp_timer_2msl()/tcp_close()/in_pcbdrop() processing. > > o Thread B wins the race: > > Thread B runs tcp_timer_2msl()/tcp_close()/in_pcbdrop() and inp > INP_DROPPED is set and inp being removed from TCP hash table. > In parallel, thread A has found the inp in TCP hash before is was > removed, and waiting on the found inp INP_WLOCK lock. > Once thread B has released the INP_WLOCK lock, thread A gets this lock > and sees the INP_DROPPED flag and do "goto findpcb" but here because the > inp is not more in TCP hash table and it will not be find again by > in_pcblookup_mbuf(). > > Hopefully I am clear enough here.
Thanks, very clear. Small qeustion: when both thread run on same CPU core, INP_WLOCK will be re-schedule? As I remeber race created by call tcp_twstart() at time of end tcp_close(), at path sofree()-tcp_usr_detach() and unexpected INP_TIMEWAIT state in the tcp_usr_detach(). INP_TIMEWAIT set in tcp_twstart() After check source code I am found invocation of tcp_twstart() in sys/netinet/tcp_stacks/fastpath.c, sys/netinet/tcp_input.c, sys/dev/cxgb/ulp/tom/cxgb_cpl_io.c, sys/dev/cxgbe/tom/t4_cpl_io.c. Invocation from sys/netinet/tcp_stacks/fastpath.c and sys/netinet/tcp_input.c guarded by INP_WLOCK in tcp_input(), and now will be OK. Invocation from sys/dev/cxgb/ulp/tom/cxgb_cpl_io.c and sys/dev/cxgbe/tom/t4_cpl_io.c is not clear to me, I am see independed INP_WLOCK. Is this OK? Can be thread A wants do_peer_close() directed from chelsio IRQ handler, bypass tcp_input()? _______________________________________________ freebsd-stable@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/freebsd-stable To unsubscribe, send any mail to "freebsd-stable-unsubscr...@freebsd.org"
