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LINUX: Avoid infinite d_invalidate loop

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In afs_linux_lookup, we try to invalidate as many dentry aliases as we
can. However, a successful d_invalidate() against a dentry does not
necessarily mean that the dentry will not show up in a later
d_find_alias() call. This is because d_invalidate() does not remove
the dentry from the d_alias list, but just removes it from the hash
chain. dput() is what removes it from the d_alias list when all of the
references go away. If a reference is grabbed between our
d_invalidate() and dput() calls, the dentry will stay on the d_alias
list.

We will then retry the loop, and we will get the same dentry back from
d_find_alias(). Running d_invalidate() on an unhashed dentry is a
no-op, so we don't change anything in the loop. We will retry again
and again, looping forever and spinning the CPU.

To avoid this, just call d_prune_aliases instead, instead of
repeatedly looping through the alias list ourselves. Note that this
does remove our check for DCACHE_DISCONNECTED in each alias' d_flags.
This should not be a problem, since we will still use any remaining
DCACHE_DISCONNECTED dentry via d_splice_alias if one still exists.

Change-Id: I8a09a922d07f2c4971269f3c681c748c33bf8e3d
Reviewed-on: http://gerrit.openafs.org/8751
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Chas Williams - CONTRACTOR <chas@cmf.nrl.navy.mil>
Reviewed-by: Marc Dionne <marc.c.dionne@gmail.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
This commit is contained in:
Andrew Deason 2012-12-12 16:14:55 -06:00 committed by Derrick Brashear
parent 8bfce8f278
commit 370aaaeafa
2 changed files with 2 additions and 36 deletions
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19
src/afs/LINUX/osi_vnodeops.c
View File

@ -1409,24 +1409,7 @@ afs_linux_lookup(struct inode *dip, struct dentry *dp)
AFS_GUNLOCK();
if (ip && S_ISDIR(ip->i_mode)) {
int retry = 1;
struct dentry *alias;
while (retry) {
retry = 0;
/* Try to invalidate an existing alias in favor of our new one */
alias = d_find_alias(ip);
/* But not if it's disconnected; then we want d_splice_alias below */
if (alias && !(alias->d_flags & DCACHE_DISCONNECTED)) {
if (d_invalidate(alias) == 0) {
/* there may be more aliases; try again until we run out */
retry = 1;
}
}
dput(alias);
}
d_prune_aliases(ip);
#ifdef STRUCT_DENTRY_OPERATIONS_HAS_D_AUTOMOUNT
ip->i_flags |= S_AUTOMOUNT;

19
src/afs/LINUX24/osi_vnodeops.c
View File

@ -1304,24 +1304,7 @@ afs_linux_lookup(struct inode *dip, struct dentry *dp)
#if defined(AFS_LINUX24_ENV)
if (ip && S_ISDIR(ip->i_mode)) {
int retry = 1;
struct dentry *alias;
while (retry) {
retry = 0;
/* Try to invalidate an existing alias in favor of our new one */
alias = d_find_alias(ip);
/* But not if it's disconnected; then we want d_splice_alias below */
if (alias) {
if (d_invalidate(alias) == 0) {
/* there may be more aliases; try again until we run out */
retry = 1;
}
}
dput(alias);
}
d_prune_aliases(ip);
}
#endif
d_add(dp, ip);