4.19-stable review patch. If anyone has any objections, please let me know.
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commit d8a706414af4827fc0b4b1c0c631c607351938b9 upstream.
get_unlocked_entry() uses an exclusive wait because it is guaranteed to 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: Matthew Wilcox willy@infradead.org Reported-by: Linus Torvalds torvalds@linux-foundation.org Reviewed-by: Jan Kara jack@suse.cz Signed-off-by: Dan Williams dan.j.williams@intel.com Signed-off-by: Sasha Levin sashal@kernel.org --- fs/dax.c | 16 +++++++--------- 1 file changed, 7 insertions(+), 9 deletions(-)
diff --git a/fs/dax.c b/fs/dax.c index 415605fafaeb..09fa70683c41 100644 --- a/fs/dax.c +++ b/fs/dax.c @@ -275,18 +275,16 @@ static void wait_entry_unlocked(struct address_space *mapping, pgoff_t index, ewait.wait.func = wake_exceptional_entry_func;
wq = dax_entry_waitqueue(mapping, index, 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); xa_unlock_irq(&mapping->i_pages); schedule(); finish_wait(wq, &ewait.wait); - - /* - * 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 unlock_mapping_entry(struct address_space *mapping, pgoff_t index)