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authorMichael I. Bushnell <mib@gnu.org>1995-04-28 00:01:12 +0000
committerMichael I. Bushnell <mib@gnu.org>1995-04-28 00:01:12 +0000
commitf47b803759a33c6cc0c27d129802e7f7e2c4d8f9 (patch)
tree5c196c3e24b879fe9c65846732af178a765366ef /libdiskfs/diskfs.h
parentb3fbfd598f8f1cb90e47855dd9096a4181c0ba4f (diff)
(diskfs_nrele, diskfs_nput): We need to hold a real reference around
the call to diskfs_try_dropping_softrefs, because that's a user-supplied routine that might itself rely on the reference counting system.
Diffstat (limited to 'libdiskfs/diskfs.h')
-rw-r--r--libdiskfs/diskfs.h45
1 files changed, 41 insertions, 4 deletions
diff --git a/libdiskfs/diskfs.h b/libdiskfs/diskfs.h
index 1d24661d..866083f0 100644
--- a/libdiskfs/diskfs.h
+++ b/libdiskfs/diskfs.h
@@ -532,17 +532,39 @@ diskfs_nref (struct node *np)
extern inline void
diskfs_nput (struct node *np)
{
+ int tried_drop_softrefs = 0;
+
+ loop:
spin_lock (&diskfs_node_refcnt_lock);
assert (np->references);
np->references--;
if (np->references + np->light_references == 0)
diskfs_drop_node (np);
- else if (np->references == 0)
+ else if (np->references == 0 && !tried_drop_softrefs)
{
spin_unlock (&diskfs_node_refcnt_lock);
diskfs_lost_hardrefs (np);
if (!np->dn_stat.st_nlink)
- diskfs_try_dropping_softrefs (np);
+ {
+ /* There are no links. If there are soft references that
+ can be dropped, we can't let them postpone deallocation.
+ So attempt to drop them. But that's a user-supplied
+ routine, which might result in further recursive calls to
+ the ref-counting system. So we have to reacquire our
+ reference around the call to forestall disaster. */
+ spin_unlock (&diskfs_node_refcnt_lock);
+ np->references++;
+ spin_unlock (&diskfs_node_refcnt_lock);
+
+ diskfs_try_dropping_softrefs (np);
+
+ /* But there's no value in looping forever in this
+ routine; only try to drop soft refs once. */
+ tried_drop_softrefs = 1;
+
+ /* Now we can drop the reference back... */
+ goto loop;
+ }
}
else
spin_unlock (&diskfs_node_refcnt_lock);
@@ -557,6 +579,9 @@ diskfs_nput (struct node *np)
extern inline void
diskfs_nrele (struct node *np)
{
+ int tried_drop_softrefs = 0;
+
+ loop:
spin_lock (&diskfs_node_refcnt_lock);
assert (np->references);
np->references--;
@@ -570,8 +595,20 @@ diskfs_nrele (struct node *np)
mutex_lock (&np->lock);
spin_unlock (&diskfs_node_refcnt_lock);
diskfs_lost_hardrefs (np);
- if (!np->dn_stat.st_nlink)
- diskfs_try_dropping_softrefs (np);
+ if (!np->dn_stat.st_nlink && !tried_drop_softrefs)
+ {
+ /* Same issue here as in nput; see that for explanation */
+ spin_unlock (&diskfs_node_refcnt_lock);
+ np->references++;
+ spin_unlock (&diskfs_node_refcnt_lock);
+
+ diskfs_try_dropping_softrefs (np);
+ tried_drop_softrefs = 1;
+
+ /* Now we can drop the reference back... */
+ mutex_unlock (&np->lock);
+ goto loop;
+ }
mutex_unlock (&np->lock);
}
else