On Fri 21-12-18 11:38:04, Dan Williams wrote:
get_unlocked_entry() uses an exclusive wait because it is guaranteed
eventually obtain the lock and follow on with an unlock+wakeup cycle.
The wait_entry_unlocked() path does not have the same guarantee. Rather
than open-code an extra wakeup, just switch to a non-exclusive wait.
Cc: Jan Kara <jack(a)suse.cz>
Cc: Matthew Wilcox <willy(a)infradead.org>
Reported-by: Linus Torvalds <torvalds(a)linux-foundation.org>
Signed-off-by: Dan Williams <dan.j.williams(a)intel.com>
fs/dax.c | 16 +++++++---------
1 file changed, 7 insertions(+), 9 deletions(-)
Thanks for cleaning this up! The patch looks good to me. You can add:
Reviewed-by: Jan Kara <jack(a)suse.cz>
diff --git a/fs/dax.c b/fs/dax.c
index 48132eca3761..042d3b31b413 100644
@@ -246,18 +246,16 @@ static void wait_entry_unlocked(struct xa_state *xas, void *entry)
ewait.wait.func = wake_exceptional_entry_func;
wq = dax_entry_waitqueue(xas, entry, &ewait.key);
- prepare_to_wait_exclusive(wq, &ewait.wait, TASK_UNINTERRUPTIBLE);
+ * Unlike get_unlocked_entry() there is no guarantee that this
+ * path ever successfully retrieves an unlocked entry before an
+ * inode dies. Perform a non-exclusive wait in case this path
+ * never successfully performs its own wake up.
+ prepare_to_wait(wq, &ewait.wait, TASK_UNINTERRUPTIBLE);
- * Entry lock waits are exclusive. Wake up the next waiter since
- * we aren't sure we will acquire the entry lock and thus wake
- * the next waiter up on unlock.
- if (waitqueue_active(wq))
- __wake_up(wq, TASK_NORMAL, 1, &ewait.key);
static void put_unlocked_entry(struct xa_state *xas, void *entry)
Jan Kara <jack(a)suse.com>
SUSE Labs, CR