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Fix lseek(SEEK_DATA/SEEK_HOLE) mmap consistency

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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
This commit is contained in:
Brian Behlendorf
2021-11-07 13:27:44 -08:00
committed by GitHub
parent 4b87c1981d
commit de198f2d95
18 changed files with 305 additions and 32 deletions
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module/zfs/dmu.c
+26 -27
View File
@@ -2093,42 +2093,41 @@ int
dmu_offset_next(objset_t *os, uint64_t object, boolean_t hole, uint64_t *off)
{
dnode_t *dn;
int i, err;
boolean_t clean = B_TRUE;
int err;
restart:
err = dnode_hold(os, object, FTAG, &dn);
if (err)
return (err);
/*
* Check if dnode is dirty
*/
for (i = 0; i < TXG_SIZE; i++) {
if (multilist_link_active(&dn->dn_dirty_link[i])) {
clean = B_FALSE;
break;
rw_enter(&dn->dn_struct_rwlock, RW_READER);
if (dnode_is_dirty(dn)) {
/*
* If the zfs_dmu_offset_next_sync module option is enabled
* then strict hole reporting has been requested. Dirty
* dnodes must be synced to disk to accurately report all
* holes. When disabled (the default) dirty dnodes are
* reported to not have any holes which is always safe.
*
* When called by zfs_holey_common() the zp->z_rangelock
* is held to prevent zfs_write() and mmap writeback from
* re-dirtying the dnode after txg_wait_synced().
*/
if (zfs_dmu_offset_next_sync) {
rw_exit(&dn->dn_struct_rwlock);
dnode_rele(dn, FTAG);
txg_wait_synced(dmu_objset_pool(os), 0);
goto restart;
}
}
/*
* If compatibility option is on, sync any current changes before
* we go trundling through the block pointers.
*/
if (!clean && zfs_dmu_offset_next_sync) {
clean = B_TRUE;
dnode_rele(dn, FTAG);
txg_wait_synced(dmu_objset_pool(os), 0);
err = dnode_hold(os, object, FTAG, &dn);
if (err)
return (err);
}
if (clean)
err = dnode_next_offset(dn,
(hole ? DNODE_FIND_HOLE : 0), off, 1, 1, 0);
else
err = SET_ERROR(EBUSY);
} else {
err = dnode_next_offset(dn, DNODE_FIND_HAVELOCK |
(hole ? DNODE_FIND_HOLE : 0), off, 1, 1, 0);
}
rw_exit(&dn->dn_struct_rwlock);
dnode_rele(dn, FTAG);
return (err);