gfs2: Fix possible data races in gfs2_show_options()

In the Linux kernel, the following vulnerability has been resolved:

gfs2: Fix possible data races in gfs2_show_options()

Some fields such as gt_logd_secs of the struct gfs2_tune are accessed

without holding the lock gt_spin in gfs2_show_options():

val = sdp->sd_tune.gt_logd_secs;

if (val != 30)

seq_printf(s, ",commit=%d", val);

And thus can cause data races when gfs2_show_options() and other functions

such as gfs2_reconfigure() are concurrently executed:

spin_lock(&gt->gt_spin);

gt->gt_logd_secs = newargs->ar_commit;

To fix these possible data races, the lock sdp->sd_tune.gt_spin is

acquired before accessing the fields of gfs2_tune and released after these

accesses.

Further changes by Andreas:

- Don't hold the spin lock over the seq_printf operations.