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* Added a clarifying comment to free_vnode() and prevented the vnode

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reference count to drop below 0 there.
* Added TODO describing a serious race condition between free_vnode()
  and the page daemon.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@22209 a95241bf-73f2-0310-859d-f6bbb57e9c96
This commit is contained in:
Ingo Weinhold 2007-09-09 14:38:58 +00:00
parent c8a342a476
commit 8687956af2
1 changed files with 21 additions and 1 deletions
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22
src/system/kernel/fs/vfs.cpp
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@ -664,7 +664,7 @@ create_new_vnode(struct vnode **_vnode, dev_t mountID, ino_t vnodeID)
static void
free_vnode(struct vnode *vnode, bool reenter)
{
ASSERT(vnode->ref_count == 0 && vnode->busy);
ASSERT_PRINT(vnode->ref_count == 0 && vnode->busy, "vnode: %p\n", vnode);
// write back any changes in this vnode's cache -- but only
// if the vnode won't be deleted, in which case the changes
@ -673,6 +673,24 @@ free_vnode(struct vnode *vnode, bool reenter)
if (!vnode->remove && FS_CALL(vnode, fsync) != NULL)
FS_CALL(vnode, fsync)(vnode->mount->cookie, vnode->private_node);
// Note: If this vnode has a cache attached, there will still be two
// references to that cache at this point. The last one belongs to the vnode
// itself (cf. vfs_get_vnode_cache()) and one belongs to the node's file
// cache. Each but the last reference to a cache also includes a reference
// to the vnode. The file cache, however, released its reference (cf.
// file_cache_create()), so that this vnode's ref count has the chance to
// ever drop to 0. Deleting the file cache now, will cause the next to last
// cache reference to be released, which will also release a (no longer
// existing) vnode reference. To avoid problems, we set the vnode's ref
// count, so that it will neither become negative nor 0.
vnode->ref_count = 2;
// TODO: Usually, when the vnode is unreferenced, no one can get hold of the
// cache either (i.e. no one can get a cache reference while we're deleting
// the vnode).. This is, however, not the case for the page daemon. It gets
// its cache references via the pages it scans, so it can in fact get a
// vnode reference while we're deleting the vnode.
if (!vnode->unpublished) {
if (vnode->remove)
FS_CALL(vnode, remove_vnode)(vnode->mount->cookie, vnode->private_node, reenter);
@ -718,6 +736,8 @@ dec_vnode_ref_count(struct vnode *vnode, bool reenter)
int32 oldRefCount = atomic_add(&vnode->ref_count, -1);
ASSERT_PRINT(oldRefCount > 0, "vnode %p\n", vnode);
TRACE(("dec_vnode_ref_count: vnode %p, ref now %ld\n", vnode, vnode->ref_count));
if (oldRefCount == 1) {