Hello all,
For a long time now, the fcntl(2) man page has carried this text
regarding mandatory (byte-range) locking:
Mandatory locking
The implementation of mandatory locking in all known versions
of Linux is subject to race conditions which render it unreli‐
able: a write(2) call that overlaps with a lock may modify data
after the mandatory lock is acquired; a read(2) call that over‐
laps with a lock may detect changes to data that were made only
after a write lock was acquired. Similar races exist between
mandatory locks and mmap(2). It is therefore inadvisable to
rely on mandatory locking.
I wanted to check: does it remain true with modern kernels that mandatory
locking is unreliable? If things have changed, an uopdate to the man page
is obviously in order.
Cheers,
Michael
--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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