Date: Tue, 29 May 2012 18:06:14 -0400 From: vasanth rao naik sabavat <vasanth.raonaik@gmail.com> To: Robert Watson <rwatson@freebsd.org> Cc: freebsd-hackers@freebsd.org Subject: Re: SMP: protocol control block protection for a multithreaded process (ex: udp). Message-ID: <CAAuizBjpLHoWwQ_CYrY9H5xrJ8_e48S_hVyU8Fif_J2pEyiq6Q@mail.gmail.com> In-Reply-To: <alpine.BSF.2.00.1205292204590.15505@fledge.watson.org> References: <CAAuizBjhGUUH3D3XN1t7WMnOPTq0vZjnV1QXGrR99qBOD34rGQ@mail.gmail.com> <CAAuizBhn_QT4WCh1ZRyc%2BHBkOYGaGivsVGm4oLj-i9VY7a5wxw@mail.gmail.com> <alpine.BSF.2.00.1205292204590.15505@fledge.watson.org>
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Hello Robert, My main concern is about the protocol control block "inp", a reference in the socket structure. the udp_detach() free'es the inp but there is a potential for other thread running udp_* functions to get hold of the reference? Also, sofree() calls SOCK_UNLOCK() which potentially may allow other thread of the same process to enter into the udp_* functions? I am not sure if that is ever possible. Thanks, Vasanth On Tue, May 29, 2012 at 5:06 PM, Robert Watson <rwatson@freebsd.org> wrote: > > On Tue, 29 May 2012, vasanth rao naik sabavat wrote: > > Can somebody please reply to this email. >> >> basically, can udp_detach() and udp_send() execute simultaneously for a >> process with multiple threads? if yes, then inp reference in udp_send() >> will be stale if udp_detach() free's the inp? >> > > You are confusing application-level close() with an actual close in the > socket implementation. The socket will remain allocated as long as there > are consumers using it, which is ensured through a reference count on the > socket, regardless of close(). That isn't to say that there aren't bugs -- > this stuff is pretty complex -- but the life cycle and synchronisation > models around sockets should prevent the scenario you are describing from > occurring. > > Robert > > >> Thanks, >> Vasanth >> >> >> >> On Tue, May 29, 2012 at 10:53 AM, vasanth rao naik sabavat < >> vasanth.raonaik@gmail.com> wrote: >> >> Hi, >>> >>> In case of a Multicore cpu system running a multithreaded process. >>> >>> For protocol control blocks there is no protection provided in the >>> FreeBSD >>> 9. For example, udp_close() and udp_send() access the inp before taking >>> the >>> lock. Couldn't this cause the inp inconsistency on a multithreaded >>> process >>> running on multicore cpu system? >>> >>> Say, If the two threads of a process are concurrently executing socket >>> send and socket close say on a udp connection (this can happen in case of >>> poorly written user code.). >>> udp_close() will access the inp on one cpu and udp_send() will access the >>> inp on another cpu. it is possible that udp_close() gets the locks first >>> and free's the inp before udp_send() has a chance to run? >>> >>> Am I missing anything? >>> >>> Thanks, >>> Vasanth >>> >>> >>> >>> >>> >>> ______________________________**_________________ >> freebsd-hackers@freebsd.org mailing list >> http://lists.freebsd.org/**mailman/listinfo/freebsd-**hackers<http://lists.freebsd.org/mailman/listinfo/freebsd-hackers>; >> To unsubscribe, send any mail to "freebsd-hackers-unsubscribe@** >> freebsd.org <freebsd-hackers-unsubscribe@freebsd.org>" >> >>
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