features / bitrot: Prevent spurious pthread_cond_wait() wakeup

pthread_cond_wait() is prone to spurious wakeups and it's utmost
necessarry to check a boolean predicate for thread continuation.

See man(3) pthread_cond_wait() for details.

The following is done in bitrot scrubber:

    if (list_empty (&fsscrub->scrublist))
       pthread_cond_wait (&fsscrub->cond, &fsscrub->mutex);

followed by:

    list_first_entry (&fsscrub->scrublist, ...)

A spurious wakeup from pthread_cond_wait() with the absence of
list_empty() check causes list_first_entry() to return garbage.

Change-Id: I08786b9686b5503fcad6127e4c2a2cfac4bb7849
BUG: 1302201
Signed-off-by: Venky Shankar <vshankar@redhat.com>
Reviewed-on: http://review.gluster.org/13302
Reviewed-by: Pranith Kumar Karampuri <pkarampu@redhat.com>
Tested-by: Pranith Kumar Karampuri <pkarampu@redhat.com>
Smoke: Gluster Build System <jenkins@build.gluster.com>
CentOS-regression: Gluster Build System <jenkins@build.gluster.com>
NetBSD-regression: NetBSD Build System <jenkins@build.gluster.org>

0 files changed, 0 insertions, 0 deletions