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?
diff --git a/fs/dax.c b/fs/dax.c
index 0fb270f0a0ef6..b8dd66f1951a6 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -227,7 +227,9 @@ static inline void *unlock_slot(struct address_space
*mapping, void **slot)
* Must be called with the i_pages lock held.
*/
static void *__get_unlocked_mapping_entry(struct address_space *mapping,
- pgoff_t index, void ***slotp, bool (*wait_fn)(void))
+ pgoff_t index, void ***slotp,
+ bool (*wait_fn)(struct address_space *mapping,
+ pgoff_t index, void *entry))
{
void *entry, **slot;
struct wait_exceptional_entry_queue ewait;
@@ -253,7 +255,7 @@ static void *__get_unlocked_mapping_entry(struct
address_space *mapping,
prepare_to_wait_exclusive(wq, &ewait.wait,
TASK_UNINTERRUPTIBLE);
xa_unlock_irq(&mapping->i_pages);
- revalidate = wait_fn();
+ revalidate = wait_fn(mapping, index, entry);
finish_wait(wq, &ewait.wait);
xa_lock_irq(&mapping->i_pages);
if (revalidate)
@@ -261,7 +263,8 @@ static void *__get_unlocked_mapping_entry(struct
address_space *mapping,
}
}
-static bool entry_wait(void)
+static bool entry_wait(struct address_space *mapping, unsigned long index,
+ void *entry)
{
schedule();
/*
@@ -393,12 +396,18 @@ static struct page *dax_busy_page(void *entry)
return NULL;
}
-static bool entry_wait_revalidate(void)
+static bool entry_wait_revalidate(struct address_space *mapping,
+ unsigned long index, void *entry)
{
rcu_read_unlock();
schedule();
rcu_read_lock();
+ /*
+ * We're not going to do anything with this entry; wake the next
+ * task in line
+ */
+ put_unlocked_mapping_entry(mapping, index, entry);
/*
* Tell __get_unlocked_mapping_entry() to take a break, we need
* to revalidate page->mapping after dropping locks
> ------------------ 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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