I found a comment from Linus Torvalds that answers this question
http://www.realworldtech.com/forum/?threadid=113923&curpostid=114068
The mapped pages are part of the filesystem cache, which means that even if the user process that made a change to that page dies, the page is still managed by the kernel and as all concurrent accesses to that file will go through the kernel, other processes will get served from that cache.
In some old Linux kernels it was different, that’s the reason why some kernel documents still tell to force msync.
EDIT: Thanks RobH corrected the link.
EDIT:
A new flag, MAP_SYNC, is introduced since Linux 4.15, which can guarantee the coherence.
Shared file mappings with this flag provide the guarantee that
while some memory is writably mapped in the address space of
the process, it will be visible in the same file at the same
offset even after the system crashes or is rebooted.
references:
http://man7.org/linux/man-pages/man2/mmap.2.html search MAP_SYNC in the page
https://lwn.net/Articles/731706/