Messages in this thread Patch in this message |  | | Subject | Re: SMP-ix86-threads-fork: Linux 2.4.x kernel problem identified [phantom read()] | From | Andreas Jaeger <> | Date | Tue, 11 Sep 2001 09:31:56 +0200 |
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Wolfram Gloger <wg@malloc.de> writes:
> Hi, > >> So it's perfectly possible to observe the behavior you are seeing >> if __libc_read() returns -1. Because then sz_read will acquire the >> value -1, and the guard expresssion sz_read < sizeof(request) will yield >> zero, terminating the loop. > > Argh! That indeed seems to be the case, _no_ apparent kernel problem > is involved, sorry for the false alarm. read() 'just' returns -1 with > errno becoming EINTR. One should never code up a loop like that in > the last minute (I only found the effect yesterday).. > >> Could you recode the test patch to eliminate these suspicions and re-test? > > The analysis was nevertheless correct, LinuxThreads gets out of synch > with disastrous effects. I was puzzled how read() could return -1, > however it may make sense with a __pthread_sig_cancel pending in the > manager thread due to a child exiting (?). But then, why wasn't this > possibility discovered before?
Because we never compiled with -DDEBUG so that the ASSERT was triggered?
There's another such place (line 135) with __libc_read in __pthread_manager:
/* Synchronize debugging of the thread manager */ n = __libc_read(reqfd, (char *)&request, sizeof(request)); ASSERT(n == sizeof(request) && request.req_kind == REQ_DEBUG);
We should account for a return value of -1 here also, shouldn't we?
> Below is a corrected patch for glibc-2.2.4. I've run fork-malloc with > this for a couple of hours.
Is it still running? ;-) That would be excellent!
Thanks a lot Wolfram, Andreas
> Thanks, > Wolfram. > > 2001-09-11 Wolfram Gloger <wg@malloc.de> > > * manager.c (__pthread_manager): When reading from pipe. account > for possible error return from read(). > > --- linuxthreads/manager.c.orig Mon Jul 23 19:54:13 2001 > +++ linuxthreads/manager.c Tue Sep 11 00:47:48 2001 > @@ -150,8 +150,19 @@ > } > /* Read and execute request */ > if (n == 1 && (ufd.revents & POLLIN)) { > - n = __libc_read(reqfd, (char *)&request, sizeof(request)); > - ASSERT(n == sizeof(request)); > + int sz_read = 0; > + > + while (sz_read < sizeof(request)) { > + n = __libc_read(reqfd, (char *)&request + sz_read, > + sizeof(request) - sz_read); > + if (n < 0) { > +#ifdef DEBUG > + char d[64]; > + sprintf(d, "*** read err %d\n", errno); > +#endif > + } else > + sz_read += n; > + } > switch(request.req_kind) { > case REQ_CREATE: > request.req_thread->p_retcode = >
-- Andreas Jaeger SuSE Labs aj@suse.de private aj@arthur.inka.de http://www.suse.de/~aj - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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