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Fix lseek(SEEK_DATA/SEEK_HOLE) mmap consistency

Description

Fix lseek(SEEK_DATA/SEEK_HOLE) mmap consistency

When using lseek(2) to report data/holes memory mapped regions of
the file were ignored. This could result in incorrect results.
To handle this zfs_holey_common() was updated to asynchronously
writeback any dirty mmap(2) regions prior to reporting holes.

Additionally, while not strictly required, the dn_struct_rwlock is
now held over the dirty check to prevent the dnode structure from
changing. This ensures that a clean dnode can't be dirtied before
the data/hole is located. The range lock is now also taken to
ensure the call cannot race with zfs_write().

Furthermore, the code was refactored to provide a dnode_is_dirty()
helper function which checks the dnode for any dirty records to
determine its dirtiness.

Reviewed-by: Matthew Ahrens <mahrens@delphix.com>
Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Reviewed-by: Rich Ercolani <rincebrain@gmail.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #11900
Closes #12724
(cherry picked from commit 664d487a5dbd758216ac613934a4080fcc1de347)

Approved by: so
Security: FreeBSD-EN-22:11.zfs

Details

Provenance
Brian Behlendorf <behlendorf1@llnl.gov>Authored on Nov 7 2021, 9:27 PM
markjCommitted on Mar 15 2022, 6:09 PM
Parents
rG0abaf7f63023: FreeBSD: Clean up zfsdev_close to match Linux
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