Hi Thomas,
Can you tell me what is the version of the lustre servers and the lustre clients ?


Thanks,

Maxime Boissonneault
HPC specialist @ Calcul Québec.

Le 2013-01-21 11:11, Thomas Rast a écrit :
Erik Faye-Lund <kusmab...@gmail.com> writes:

On Fri, Jan 18, 2013 at 6:50 PM, Eric Chamberland
<eric.chamberl...@giref.ulaval.ca> wrote:
Good idea!

I did a strace and here is the output with the error:

http://www.giref.ulaval.ca/~ericc/strace_git_error.txt

Hope it will be insightful!
This trace doesn't seem to contain child-processes, but instead having
their stderr inlined into the log. Try using "strace -f" instead...
I happen to have access to a lustre FS on the brutus cluster of ETH
Zurich, so I figured I could give it a shot.

What's odd is that while I cannot reproduce the original problem, there
seems to be another issue/bug with utime():

   $ strace -f -o ~/gc.trace git gc
   warning: failed utime() on .git/objects/68/tmp_obj_sCAEVc: Interrupted 
system call
   warning: failed utime() on .git/objects/a6/tmp_obj_3cdB2c: Interrupted 
system call
   warning: failed utime() on .git/objects/69/tmp_obj_lbU3Xc: Interrupted 
system call
   warning: failed utime() on .git/objects/c3/tmp_obj_EU97Wc: Interrupted 
system call
   warning: failed utime() on .git/objects/3e/tmp_obj_tb2j3c: Interrupted 
system call
   warning: failed utime() on .git/objects/15/tmp_obj_e6zMXc: Interrupted 
system call
   warning: failed utime() on .git/objects/54/tmp_obj_ExOJVc: Interrupted 
system call
   warning: failed utime() on .git/objects/e3/tmp_obj_GtPw4c: Interrupted 
system call
   warning: failed utime() on .git/objects/21/tmp_obj_Xex32c: Interrupted 
system call
   warning: failed utime() on .git/objects/1a/tmp_obj_CzwsZc: Interrupted 
system call
   warning: failed utime() on .git/objects/18/tmp_obj_o6fp3c: Interrupted 
system call
   warning: failed utime() on .git/objects/32/tmp_obj_Ih0G4c: Interrupted 
system call
   warning: failed utime() on .git/objects/41/tmp_obj_1RXV1c: Interrupted 
system call
   Counting objects: 137744, done.
   Delta compression using up to 48 threads.
   Compressing objects: 100% (36510/36510), done.
   Writing objects: 100% (137744/137744), done.
   Total 137744 (delta 101591), reused 135512 (delta 99472)

The trace is here (2.1MB compressed):

   http://thomasrast.ch/download/gc.trace.bz2

For the test I used a clone of another git.git I had around.  I think
the error is from sha1_file.c:2564.  While that doesn't look too
important (see ca11b212 for context), it does raise the question: what
other system calls that we never expect to EINTR can do this on
sufficiently arcane system/FS combinations?


Peff's test ran without any apparent issue for a few minutes.  I also
ran an extended version (at the end) that sets alarms, so as to actually
get interrupted.  That proved more interesting.  I had to fix verify()
and write_in_full() to account for EINTR in read()/write(), as those
seem likely to fail.  I also got link() to fail:

   $ ~/lustre-peff-reproducer
   unable to create hard link: Interrupted system call
   unable to open index file: No such file or directory

but it took a long time.  Unfortunately, when running it with strace I
managed to panic the host I ran it on:

   $ strace -o ~/peff-reproducer.trace ~/lustre-peff-reproducer

   Message from syslogd@brutus1 at Jan 21 17:09:43 ...
    kernel:LustreError: 37417:0:(osc_lock.c:1182:osc_lock_enqueue()) ASSERTION( 
ols->ols_state == OLS_NEW ) failed: Impossible state: 4

   Message from syslogd@brutus1 at Jan 21 17:09:43 ...
    kernel:LustreError: 37417:0:(osc_lock.c:1182:osc_lock_enqueue()) LBUG

   Message from syslogd@brutus1 at Jan 21 17:09:43 ...
    kernel:Kernel panic - not syncing: LBUG

Yay for now having to explain this to the cluster team.


I tried finding a standard that limits the syscalls to which EINTR
applies, without too much success.  I'm not sure how far I should trust
my manpages, but while some of them explicitly list EINTR as a possible
error (read, write, etc.) link() does not.  (And the linux manpages
agree with the POSOIX ones for once.)

If somebody finds such a standard, we could of course use it to blame
lustre instead :-)

In the absence of it, wouldn't we in theory have to write a simple
loop-on-EINTR wrapper for *all* syscalls?

Of course there's the added problem that when open(O_CREAT|O_EXCL) fails
with EINTR, it's hard to tell whether a file that may now exist is
indeed yours or some other process's.

--- 8< ----
#include <fcntl.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <sys/time.h>
#include <signal.h>
#include <errno.h>

struct itimerval itv;

static int randomize(unsigned char *buf, int len)
{
   int i;
   len = rand() % len;
   for (i = 0; i < len; i++)
     buf[i] = rand() & 0xff;
   return len;
}

static int check_eof(int fd)
{
   int ch;
   int r = read(fd, &ch, 1);
   if (r < 0) {
     perror("read error after expected EOF");
     return -1;
   }
   if (r > 0) {
     fprintf(stderr, "extra byte after expected EOF");
     return -1;
   }
   return 0;
}

static int verify(int fd, const unsigned char *buf, int len)
{
   while (len) {
     char to_check[4096];
     int got = read(fd, to_check,
                    len < sizeof(to_check) ? len : sizeof(to_check));

     if (got < 0 && errno == EINTR)
       continue;
     if (got < 0) {
       perror("unable to read");
       return -1;
     }
     if (got == 0) {
       fprintf(stderr, "premature EOF (%d bytes remaining)", len);
       return -1;
     }
     if (memcmp(buf, to_check, got)) {
       fprintf(stderr, "bytes differ");
       return -1;
     }

     buf += got;
     len -= got;
   }

   return check_eof(fd);
}

int write_in_full(int fd, const unsigned char *buf, int len)
{
   while (len) {
     int r = write(fd, buf, len);
     if (r < 0 && errno == EINTR)
       continue;
     if (r < 0)
       return -1;
     buf += r;
     len -= r;
   }
   return 0;
}

int move_into_place(const char *old, const char *new)
{
   if (link(old, new) < 0) {
     perror("unable to create hard link");
     return 1;
   }
   unlink(old);
   return 0;
}

void handle_alarm(int signal)
{
}

int main(void)
{
   struct sigaction sa;

   sa.sa_handler = handle_alarm;
   sa.sa_flags = SA_RESTART;
   sigaction(SIGALRM, &sa, NULL);

   itv.it_interval.tv_sec = 0;
   itv.it_interval.tv_usec = 10000;
   itv.it_value.tv_sec = 0;
   itv.it_value.tv_usec = 100000;
   setitimer(ITIMER_REAL, &itv, NULL);

   while (1) {
     static unsigned char junk[1024*1024];
     int len = randomize(junk, sizeof(junk));
     int fd;

     /* clean up from any previous round */
     unlink("tmpfile");
     unlink("final.idx");

     fd = open("tmpfile", O_WRONLY|O_CREAT, 0666);
     if (fd < 0) {
       perror("unable to open tmpfile");
       return 1;
     }
     if (write_in_full(fd, junk, len) < 0 ||
         fsync(fd) < 0 ||
         close(fd) < 0) {
       perror("unable to write");
       return 1;
     }

     if (move_into_place("tmpfile", "final.idx") < 0)
       return 1;

     fd = open("final.idx", O_RDONLY);
     if (fd < 0) {
       perror("unable to open index file");
       return 1;
     }
     if (verify(fd, junk, len) < 0)
       return 1;
     close(fd);
   }
}


--
---------------------------------
Maxime Boissonneault
Analyste de calcul - Calcul Québec, Université Laval
Ph. D. en physique

--
To unsubscribe from this list: send the line "unsubscribe git" in
the body of a message to majord...@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Reply via email to