On Fri, 2007-02-02 at 14:28 -0500, Aaron Wiebe wrote:
> Greetings,
>
> I've run into a situation where fcntl F_SETLKW calls lock up nearly
> completely. I've tried several approaches to handle this case, and
> have yet to come up with some method of handling this. I've never
> really ventured outside userspace, so I'm turning to this list to try
> and get a handle on this.
>
> Over NFSv3 udp, this situation takes place VERY rarely, however with
> the volume I do, its creating a problem.
>
> In short, I am attempting to read or write lock, and the call hangs to
> the point where a sigkill is not captured - no signal is. I've tried
> alarming out and I've tried switching the socket to nonblocking -
> nothing I can think of prevents or even allows me to handle the case.
> I understand NFS locking can be rather sketchy at times - but all I
> need is the ability to handle the case.
>
> I can force the process to die by sending a sigkill, then stracing.
> The strace reports the process as sigstop, then processes the kill
> signal.
>
> All I need here is a method of capturing this case. I can "repair"
> the stuck lock by regenerating the file, but I can't capture the case
> in order to handle this in code.
>
> Any help would be useful - I am currently running 2.6.15.6 compiled
> with the NFS patches from linux-nfs.org, but this case was happening
> before applying those patches. I'd be happy to provide any more
> information nessecary. I've been struggling with this one for a few
> months now.
>
> Thanks,
> -Aaron
>
>
> Straces:
>
> rt_sigaction(SIGALRM, {0xb7f56640, [ALRM], 0}, {SIG_DFL}, 8) = 0
> alarm(120) = 0
> fcntl64(3, F_SETLKW, {type=F_RDLCK, whence=SEEK_SET, start=0, len=0}
> [hangs]
>
> Or:
>
> fcntl64(3, F_GETFL) = 0x8002 (flags O_RDWR|O_LARGEFILE)
> fcntl64(3, F_SETFL, O_RDWR|O_NONBLOCK|O_LARGEFILE) = 0
> fcntl64(3, F_SETLKW, {type=F_RDLCK, whence=SEEK_SET, start=0, len=0}
>
>
>
> Code used for locking:
>
> static int db_lock(int fd, int type)
> {
> struct flock fl;
> struct timespec *tv = (struct timespec *) malloc(sizeof(struct timespec));
> int ret, c = 0;
>
> if(!(fd > 0))
> return -1;
>
> #ifdef SIGALRM_HACK
> /* after two minutes, wig out */
> sigalrm_set();
> alarm(120);
> #endif
>
> fl.l_whence = SEEK_SET;
> fl.l_start = 0;
> fl.l_len = 0;
> fl.l_type = type;
>
> #ifdef NONBLOCKING_HACK
> set_nonblocking(fd);
> #endif
>
> while((ret = fcntl(fd, F_SETLKW, &fl)) < 0)
> {
> c++;
> if(c > 600)
> {
> /* we've been waiting for 60 seconds... */
> my_error("stuck on fcntl request, aborting");
> return -1;
> }
> tv->tv_nsec = 100; /* 10th of a second wait */
> tv->tv_sec = 0;
> nanosleep(tv, NULL);
> }
> free(tv);
> #ifdef SIGALRM_HACK
> sigalrm_unset();
> #endif
> #ifdef NONBLOCKING_HACK
> unset_nonblocking(fd);
> #endif
> return ret;
> }
Should have been fixed in mainline in 2.6.16 by the following patch
http://linux-nfs.org/cgi-bin/gitweb.cgi?p=nfs-2.6.git;a=commitdiff;h=a9a801787a761616589a6526d7a29c13f4deb3d8;hp=03f28e3a2059fc466761d872122f30acb7be61ae
Cheers,
Trond
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