On Thu, Apr 16 2009, Jeff Moyer wrote:
> Hi,
>
> I ran into a problem when specifying -D dirname-that-doesnt-yet-exist.
> Blktrace would fail, spewing the following messages:
>
> [root@megadeth blktrace]# ./blktrace -d /dev/cciss/c0d1 -D ./2.6.30-rc2-cfq-local
> Destination dir ./2.6.30-rc2-cfq-local/ can't be made: 17/File exists
> Destination dir ./2.6.30-rc2-cfq-local/ can't be made: 17/File exists
> Destination dir ./2.6.30-rc2-cfq-local/ can't be made: 17/File exists
> Destination dir ./2.6.30-rc2-cfq-local/ can't be made: 17/File exists
> Destination dir ./2.6.30-rc2-cfq-local/ can't be made: 17/File exists
> FAILED to start thread on CPU 0: 1/Operation not permitted
> FAILED to start thread on CPU 4: 1/Operation not permitted
> FAILED to start thread on CPU 5: 1/Operation not permitted
> FAILED to start thread on CPU 6: 1/Operation not permitted
> FAILED to start thread on CPU 7: 1/Operation not permitted
>
> I tracked it down to the fact that there is no synchronization between
> threads when trying to create the output directory. The fix is simple,
> just allow the race to happen and detect it. It's not really worth
> putting in any extra synchronization. It looks like no place else in
> that startup path needs synchronization either.
>
> This patch fixes the issue for me. I tested it by running the very
> command that caused me headaches 100% of the time before. I also did a
> chattr +i on the directory and verified that it would really fail in the
> case where it couldn't create the directory.
>
> Cheers,
> Jeff
>
> diff --git a/blktrace.c b/blktrace.c
> index 656ab7a..b4c919d 100644
> --- a/blktrace.c
> +++ b/blktrace.c
> @@ -1477,7 +1477,12 @@ static int fill_ofname(struct io_info *iop, int cpu)
> iop->ofn, errno, strerror(errno));
> return 1;
> }
> - if (mkdir(iop->ofn, 0755) < 0) {
> + /*
> + * There is no synchronization between multiple threads
> + * trying to create the directory at once. It's harmless
> + * to let them try, so just detect the problem and move on.
> + */
> + if (mkdir(iop->ofn, 0755) < 0 && errno != EEXIST) {
> fprintf(stderr,
> "Destination dir %s can't be made: %d/%s\n",
> iop->ofn, errno, strerror(errno));
Thanks Jeff, applied!
--
Jens Axboe
--
To unsubscribe from this list: send the line "unsubscribe linux-btrace" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
