[Devel] [PATCH RH7] pfcache: do not drop pfcache checksum during mmap(SHARED) of ro-files

[Vasily Averin]

Currently any mmap(SHARED) removes pfcache mark, even for
read_only-opened files. It is required to guarantee that
shared mappings will see changes if mapped file will be
write-opened and modified.

On the other hand we do not want to drop pfcache mark without
necessary. At present ldconfig calls mmap(SHARED) before adding of
any new files into library cache. It removes pfcache mark and
do not allow to add libraries into pfcache.

This patch help to avoid the problem: during mmap(SHARED) for read-only
files kernel do not drop pfcache mark from inode but close file in
pfcache area and use its local copy.

In fact such mappings can be linked back to pfcache file,
via ext4_relink_pfcache() called during fs remount, however I believe it
is extremely rare situation and even if this happen it's unlikely
lead to troubles.

https://jira.sw.ru/browse/PSBM-64045
Signed-off-by: Vasily Averin <vvs at virtuozzo.com>
---
 fs/ext4/file.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/fs/ext4/file.c b/fs/ext4/file.c
index 5acd8ae38db2..ed31192cdaa8 100644
--- a/fs/ext4/file.c
+++ b/fs/ext4/file.c
@@ -363,7 +363,10 @@ static int ext4_file_mmap(struct file *file, struct vm_area_struct *vma)
 	if (!vma) {
 		if (ext4_test_inode_state(inode, EXT4_STATE_PFCACHE_CSUM)) {
 			mutex_lock(&inode->i_mutex);
-			ext4_truncate_data_csum(inode, -1);
+			if (file->f_mode & FMODE_WRITE)
+				ext4_truncate_data_csum(inode, -1);
+			else
+				ext4_close_pfcache(inode);
 			mutex_unlock(&inode->i_mutex);
 		}
 		return 0;
-- 
2.17.1