On Sat, Oct 19, 2019 at 09:26:19AM -0700, Dan Williams wrote:
> Check for NULL entries before checking the entry order, otherwise NULL
> is misinterpreted as a present pte conflict. The 'order' check needs to
> happen before the locked check as an unlocked entry at the wrong order
> must fallback to lookup the correct order.
>
> Reported-by: Jeff Smits <jeff.smits@xxxxxxxxx>
> Reported-by: Doug Nelson <doug.nelson@xxxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx>
> Fixes: 23c84eb78375 ("dax: Fix missed wakeup with PMD faults")
> Cc: Jan Kara <jack@xxxxxxx>
> Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
> Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
> ---
> fs/dax.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/fs/dax.c b/fs/dax.c
> index a71881e77204..08160011d94c 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -221,10 +221,11 @@ static void *get_unlocked_entry(struct xa_state *xas, unsigned int order)
>
> for (;;) {
> entry = xas_find_conflict(xas);
> + if (!entry || WARN_ON_ONCE(!xa_is_value(entry)))
> + return entry;
> if (dax_entry_order(entry) < order)
> return XA_RETRY_ENTRY;
> - if (!entry || WARN_ON_ONCE(!xa_is_value(entry)) ||
> - !dax_is_locked(entry))
> + if (!dax_is_locked(entry))
> return entry;
Yes, I think this works. Should we also add:
static unsigned int dax_entry_order(void *entry)
{
+ BUG_ON(!xa_is_value(entry));
if (xa_to_value(entry) & DAX_PMD)
return PMD_ORDER;
return 0;
}
which would have caught this logic error before it caused a performance
regression?
