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Main part here is making parallel lookups safe for RT - making

Browse source 
sure preemption is disabled in start_dir_add()/ end_dir_add() sections (on
 non-RT it's automatic, on RT it needs to to be done explicitly) and moving
 wakeups from __d_lookup_done() inside of such to the end of those sections.
 	Wakeups can be safely delayed for as long as ->d_lock on in-lookup
 dentry is held; proving that has caught a bug in d_add_ci() that allows
 memory corruption when sufficiently bogus ntfs (or case-insensitive xfs)
 image is mounted.  Easily fixed, fortunately.
 
 Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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Merge tag 'pull-work.dcache' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs

Pull vfs dcache updates from Al Viro:
 "The main part here is making parallel lookups safe for RT - making
  sure preemption is disabled in start_dir_add()/ end_dir_add() sections
  (on non-RT it's automatic, on RT it needs to to be done explicitly)
  and moving wakeups from __d_lookup_done() inside of such to the end of
  those sections.

  Wakeups can be safely delayed for as long as ->d_lock on in-lookup
  dentry is held; proving that has caught a bug in d_add_ci() that
  allows memory corruption when sufficiently bogus ntfs (or
  case-insensitive xfs) image is mounted. Easily fixed, fortunately"

* tag 'pull-work.dcache' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs:
  fs/dcache: Move wakeup out of i_seq_dir write held region.
  fs/dcache: Move the wakeup from __d_lookup_done() to the caller.
  fs/dcache: Disable preemption on i_dir_seq write side on PREEMPT_RT
  d_add_ci(): make sure we don't miss d_lookup_done()
This commit is contained in:
Linus Torvalds 2022-08-03 11:43:12 -07:00
commit 200e340f21
2 changed files with 46 additions and 17 deletions
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9
include/linux/dcache.h
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@ -349,7 +349,7 @@ static inline void dont_mount(struct dentry *dentry)
spin_unlock(&dentry->d_lock);
}
extern void __d_lookup_done(struct dentry *);
extern void __d_lookup_unhash_wake(struct dentry *dentry);
static inline int d_in_lookup(const struct dentry *dentry)
{
@ -358,11 +358,8 @@ static inline int d_in_lookup(const struct dentry *dentry)
static inline void d_lookup_done(struct dentry *dentry)
{
if (unlikely(d_in_lookup(dentry))) {
spin_lock(&dentry->d_lock);
__d_lookup_done(dentry);
spin_unlock(&dentry->d_lock);
}
if (unlikely(d_in_lookup(dentry)))
__d_lookup_unhash_wake(dentry);
}
extern void dput(struct dentry *);