From 1ac5cd4978794bd060d448acc0305e9fc996ba92 Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Wed, 2 Jan 2019 10:46:03 -0800 Subject: block: don't use un-ordered __set_current_state(TASK_UNINTERRUPTIBLE) This mostly reverts commit 849a370016a5 ("block: avoid ordered task state change for polled IO"). It was wrongly claiming that the ordering wasn't necessary. The memory barrier _is_ necessary. If something is truly polling and not going to sleep, it's the whole state setting that is unnecessary, not the memory barrier. Whenever you set your state to a sleeping state, you absolutely need the memory barrier. Note that sometimes the memory barrier can be elsewhere. For example, the ordering might be provided by an external lock, or by setting the process state to sleeping before adding yourself to the wait queue list that is used for waking up (where the wait queue lock itself will guarantee that any wakeup will correctly see the sleeping state). But none of those cases were true here. NOTE! Some of the polling paths may indeed be able to drop the state setting entirely, at which point the memory barrier also goes away. (Also note that this doesn't revert the TASK_RUNNING cases: there is no race between a wakeup and setting the process state to TASK_RUNNING, since the end result doesn't depend on ordering). Cc: Jens Axboe Cc: Christoph Hellwig Signed-off-by: Linus Torvalds --- mm/page_io.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) (limited to 'mm/page_io.c') diff --git a/mm/page_io.c b/mm/page_io.c index 3475733b1926..d975fa3f02aa 100644 --- a/mm/page_io.c +++ b/mm/page_io.c @@ -405,8 +405,7 @@ int swap_readpage(struct page *page, bool synchronous) bio_get(bio); qc = submit_bio(bio); while (synchronous) { - __set_current_state(TASK_UNINTERRUPTIBLE); - + set_current_state(TASK_UNINTERRUPTIBLE); if (!READ_ONCE(bio->bi_private)) break; -- cgit