[PATCH 2/2] fs/select: mark select and poll tasks TASK_FREEZABLE

[Sadrul Chowdhury <sadrul@google.com>]

Similar to epoll_wait(), threads sleeping in do_select() and do_poll()
sleep in TASK_INTERRUPTIBLE via poll_schedule_timeout(). During system
suspend and resume, these threads are woken up by the freezer solely to
transition to TASK_FROZEN, and woken again upon thaw only to re-evaluate
file descriptors with no pending activity and sleep again.

A previous attempt to make select() and poll() freezable in commit
9745cdb36da8 ("select: use freezable blocking call") was reverted in
commit 59612d187912 ("Revert "select: use freezable blocking call"")
alongside the epoll revert due to issues caused by the legacy freezer
architecture.

Following the freezer overhaul in commit f5d39b020809 ("freezer,sched:
Rewrite core freezer logic"), tasks in TASK_FREEZABLE are safely frozen
in-place into TASK_FROZEN without running userspace code or experiencing
premature wakeups before resume completes.

Pass TASK_FREEZABLE to poll_schedule_timeout() in do_select() and
do_poll() (TASK_INTERRUPTIBLE | TASK_FREEZABLE) so that polling threads
remain asleep undisturbed across suspend/resume cycles.

Signed-off-by: Sadrul Chowdhury <sadrul@google.com>
---
 fs/select.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/select.c b/fs/select.c
index 8943f20e8300..5cbbe86135bc 100644
--- a/fs/select.c
+++ b/fs/select.c
@@ -601,7 +601,7 @@ static noinline_for_stack int do_select(int n, fd_set_bits *fds, struct timespec
 			to = &expire;
 		}
 
-		if (!poll_schedule_timeout(&table, TASK_INTERRUPTIBLE,
+		if (!poll_schedule_timeout(&table, TASK_INTERRUPTIBLE | TASK_FREEZABLE,
 					   to, slack))
 			timed_out = 1;
 	}
@@ -961,7 +961,7 @@ static int do_poll(struct poll_list *list, struct poll_wqueues *wait,
 			to = &expire;
 		}
 
-		if (!poll_schedule_timeout(wait, TASK_INTERRUPTIBLE, to, slack))
+		if (!poll_schedule_timeout(wait, TASK_INTERRUPTIBLE | TASK_FREEZABLE, to, slack))
 			timed_out = 1;
 	}
 	return count;
-- 
2.55.0.1082.g2b9226bbc0-goog