On Mon, Nov 26, 2018 at 04:22:23AM -0800, Matthew Wilcox wrote:
> On Mon, Nov 26, 2018 at 11:40:20AM +0100, [email protected] wrote:
> >
> > The patch below does not apply to the 4.19-stable tree.
> > If someone wants it applied there, or to any other stable or longterm
> > tree, then please email the backport, including the original git commit
> > id to <[email protected]>.
>
> The fix for 4.19 is rather more complex because we don't have the
> right information in the right places. Dan, does this look right to you?
Wait, we can do it like this which should be simpler:
diff --git a/fs/dax.c b/fs/dax.c
index 0fb270f0a0ef6..b0cd1364c68fa 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -217,6 +217,9 @@ static inline void *unlock_slot(struct address_space
*mapping, void **slot)
return (void *)entry;
}
+static void put_unlocked_mapping_entry(struct address_space *mapping,
+ pgoff_t index, void *entry);
+
/*
* Lookup entry in radix tree, wait for it to become unlocked if it is
* exceptional entry and return it. The caller must call
@@ -256,8 +259,10 @@ static void *__get_unlocked_mapping_entry(struct
address_space *mapping,
revalidate = wait_fn();
finish_wait(wq, &ewait.wait);
xa_lock_irq(&mapping->i_pages);
- if (revalidate)
+ if (revalidate) {
+ put_unlocked_mapping_entry(mapping, index, entry);
return ERR_PTR(-EAGAIN);
+ }
}
}
> > ------------------ original commit in Linus's tree ------------------
> >
> > >From 25bbe21bf427a81b8e3ccd480ea0e1d940256156 Mon Sep 17 00:00:00 2001
> > From: Matthew Wilcox <[email protected]>
> > Date: Fri, 16 Nov 2018 15:50:02 -0500
> > Subject: [PATCH] dax: Avoid losing wakeup in dax_lock_mapping_entry
> >
> > After calling get_unlocked_entry(), you have to call
> > put_unlocked_entry() to avoid subsequent waiters losing wakeups.
> >
> > Fixes: c2a7d2a11552 ("filesystem-dax: Introduce dax_lock_mapping_entry()")
> > Cc: [email protected]
> > Signed-off-by: Matthew Wilcox <[email protected]>
> >
> > diff --git a/fs/dax.c b/fs/dax.c
> > index cf2394e2bf4b..9bcce89ea18e 100644
> > --- a/fs/dax.c
> > +++ b/fs/dax.c
> > @@ -391,6 +391,7 @@ bool dax_lock_mapping_entry(struct page *page)
> > rcu_read_unlock();
> > entry = get_unlocked_entry(&xas);
> > xas_unlock_irq(&xas);
> > + put_unlocked_entry(&xas, entry);
> > rcu_read_lock();
> > continue;
> > }
> >
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