diff options
| author | Linus Torvalds <torvalds@linux-foundation.org> | 2026-04-21 07:30:44 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2026-04-21 07:30:44 -0700 |
| commit | 292a2bcd172662c7f281a7d79b095c91101c2e32 (patch) | |
| tree | cdf73bc18496915cd8e8deb1eea1746a8bc491be /include/linux | |
| parent | b4e07588e743c989499ca24d49e752c074924a9a (diff) | |
| parent | 14a51045e10d3087b8374deef02a9d3a694132d6 (diff) | |
Merge tag 'pull-dcache-busy-wait' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs
Pull dcache busy loop updates from Al Viro:
"Fix livelocks in shrink_dcache_tree()
If shrink_dcache_tree() finds a dentry in the middle of being killed
by another thread, it has to wait until the victim finishes dying,
gets detached from the tree and ceases to pin its parent.
The way we used to deal with that amounted to busy-wait;
unfortunately, it's not just inefficient but can lead to reliably
reproducible hard livelocks.
Solved by having shrink_dentry_tree() attach a completion to such
dentry, with dentry_unlist() calling complete() on all objects
attached to it. With a bit of care it can be done without growing
struct dentry or adding overhead in normal case"
* tag 'pull-dcache-busy-wait' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs:
get rid of busy-waiting in shrink_dcache_tree()
dcache.c: more idiomatic "positives are not allowed" sanity checks
struct dentry: make ->d_u anonymous
for_each_alias(): helper macro for iterating through dentries of given inode
Diffstat (limited to 'include/linux')
| -rw-r--r-- | include/linux/dcache.h | 24 |
1 files changed, 20 insertions, 4 deletions
diff --git a/include/linux/dcache.h b/include/linux/dcache.h index c5bd5a74baba..2577c05f84ec 100644 --- a/include/linux/dcache.h +++ b/include/linux/dcache.h @@ -88,6 +88,7 @@ union shortname_store { #define d_lock d_lockref.lock #define d_iname d_shortname.string +struct completion_list; struct dentry { /* RCU lookup touched fields */ @@ -122,13 +123,24 @@ struct dentry { struct hlist_node d_sib; /* child of parent list */ struct hlist_head d_children; /* our children */ /* - * d_alias and d_rcu can share memory + * the following members can share memory - their uses are + * mutually exclusive. */ union { - struct hlist_node d_alias; /* inode alias list */ - struct hlist_bl_node d_in_lookup_hash; /* only for in-lookup ones */ + /* positives: inode alias list */ + struct hlist_node d_alias; + /* in-lookup ones (all negative, live): hash chain */ + struct hlist_bl_node d_in_lookup_hash; + /* killed ones: (already negative) used to schedule freeing */ struct rcu_head d_rcu; - } d_u; + /* + * live non-in-lookup negatives: used if shrink_dcache_tree() + * races with eviction by another thread and needs to wait for + * this dentry to get killed . Remains NULL for almost all + * negative dentries. + */ + struct completion_list *waiters; + }; }; /* @@ -616,4 +628,8 @@ void set_default_d_op(struct super_block *, const struct dentry_operations *); struct dentry *d_make_persistent(struct dentry *, struct inode *); void d_make_discardable(struct dentry *dentry); +/* inode->i_lock must be held over that */ +#define for_each_alias(dentry, inode) \ + hlist_for_each_entry(dentry, &(inode)->i_dentry, d_alias) + #endif /* __LINUX_DCACHE_H */ |