LU-13137 llite: do not flush COW pages from mapping

LU-13137 llite: do not flush COW pages from mapping

Do not flush COW pages from an executable mapping, as this will cause
running binaries to segfault when mapped pages disappear under them.

This was modified to allow non-blocking PCC caching, but triggers
immediate segfaults for binaries when the DLM locks are revoked, even
when PCC is not in use.

The added test case failed 100% without this patch.

This patch is only a partial fix to avoid the segfaults.  There still
needs to be something done to re-introduce the PCC functionality, but
should be conditional on PCC enabled, and not for running binaries.

There is a problem for PCC when multiple clients read/write on a
shared mmapped file. We exclude mmap_sanity tst6 in test_4 from
PCC testing temporarily.

Test-Parameters: testlist=sanity envdefinitions=ONLY=30d
Test-Parameters: testlist=sanity envdefinitions=ONLY=30d
Test-Parameters: testlist=sanity envdefinitions=ONLY=30d
Fixes: 58d744e3eaab ("LU-10092 pcc: Non-blocking PCC caching")
Change-Id: I7084e1db1f0f29cb0237b619abd33ca556aa7ec7
Signed-off-by: Bobi Jam <bobijam@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/37278
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Yingjin Qian <qian@ddn.com>
Reviewed-by: Stephan Thiell <sthiell@stanford.edu>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>