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OpenZFS 9880 - Race in ZFS parallel mount

Porting Notes:
* Not required for Linux since the zone is always global.  But
  we'll want this change if we start using the zones code.

Authored by: Andy Fiddaman <omnios@citrus-it.co.uk>
Reviewed by: Jason King <jason.king@joyent.com>
Reviewed by: Sebastien Roy <sebastien.roy@delphix.com>
Approved by: Joshua M. Clulow <josh@sysmgr.org>
Ported-by: Brian Behlendorf <behlendorf1@llnl.gov>

OpenZFS-issue: https://www.illumos.org/issues/9880
OpenZFS-commit: openzfs/openzfs@bc4c0ff
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citrus-it authored and behlendorf committed Oct 20, 2018
1 parent b53cb02 commit 4623aba1908a95fae07dfdcec5eee9a29558d7ee
Showing with 31 additions and 3 deletions.
  1. +31 −3 lib/libzfs/libzfs_mount.c
@@ -26,6 +26,7 @@
* Copyright 2016 Igor Kozhukhov <ikozhukhov@gmail.com>
* Copyright 2017 RackTop Systems.
* Copyright (c) 2018 Datto Inc.
* Copyright 2018 OmniOS Community Edition (OmniOSce) Association.
*/
/*
@@ -1217,19 +1218,28 @@ zfs_iter_cb(zfs_handle_t *zhp, void *data)
/*
* Sort comparator that compares two mountpoint paths. We sort these paths so
* that subdirectories immediately follow their parents. This means that we
* effectively treat the '/' character as the lowest value non-nul char. An
* example sorted list using this comparator would look like:
* effectively treat the '/' character as the lowest value non-nul char.
* Since filesystems from non-global zones can have the same mountpoint
* as other filesystems, the comparator sorts global zone filesystems to
* the top of the list. This means that the global zone will traverse the
* filesystem list in the correct order and can stop when it sees the
* first zoned filesystem. In a non-global zone, only the delegated
* filesystems are seen.
*
* An example sorted list using this comparator would look like:
*
* /foo
* /foo/bar
* /foo/bar/baz
* /foo/baz
* /foo.bar
* /foo (NGZ1)
* /foo (NGZ2)
*
* The mounting code depends on this ordering to deterministically iterate
* over filesystems in order to spawn parallel mount tasks.
*/
int
static int
mountpoint_cmp(const void *arga, const void *argb)
{
zfs_handle_t *const *zap = arga;
@@ -1241,6 +1251,14 @@ mountpoint_cmp(const void *arga, const void *argb)
const char *a = mounta;
const char *b = mountb;
boolean_t gota, gotb;
uint64_t zoneda, zonedb;
zoneda = zfs_prop_get_int(za, ZFS_PROP_ZONED);
zonedb = zfs_prop_get_int(zb, ZFS_PROP_ZONED);
if (zoneda && !zonedb)
return (1);
if (!zoneda && zonedb)
return (-1);
gota = (zfs_get_type(za) == ZFS_TYPE_FILESYSTEM);
if (gota) {
@@ -1461,6 +1479,8 @@ void
zfs_foreach_mountpoint(libzfs_handle_t *hdl, zfs_handle_t **handles,
size_t num_handles, zfs_iter_f func, void *data, boolean_t parallel)
{
zoneid_t zoneid = getzoneid();
/*
* The ZFS_SERIAL_MOUNT environment variable is an undocumented
* variable that can be used as a convenience to do a/b comparison
@@ -1495,6 +1515,14 @@ zfs_foreach_mountpoint(libzfs_handle_t *hdl, zfs_handle_t **handles,
*/
for (int i = 0; i < num_handles;
i = non_descendant_idx(handles, num_handles, i)) {
/*
* Since the mountpoints have been sorted so that the zoned
* filesystems are at the end, a zoned filesystem seen from
* the global zone means that we're done.
*/
if (zoneid == GLOBAL_ZONEID &&
zfs_prop_get_int(handles[i], ZFS_PROP_ZONED))
break;
zfs_dispatch_mount(hdl, handles, num_handles, i, func, data,
tp);
}

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