[PATCH 2/7] io_uring: handle signals for IO threads like a normal thread

[Jens Axboe]

We go through various hoops to disallow signals for the IO threads, but
there's really no reason why we cannot just allow them. The IO threads
never return to userspace like a normal thread, and hence don't go through
normal signal processing. Instead, just check for a pending signal as part
of the work loop, and call get_signal() to handle it for us if anything
is pending.

With that, we can support receiving signals, including special ones like
SIGSTOP.

Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
---
 fs/io-wq.c    | 24 +++++++++++++++++-------
 fs/io_uring.c | 12 ++++++++----
 2 files changed, 25 insertions(+), 11 deletions(-)

diff --git a/fs/io-wq.c b/fs/io-wq.c
index b7c1fa932cb3..3e2f059a1737 100644
--- a/fs/io-wq.c
+++ b/fs/io-wq.c
@@ -16,7 +16,6 @@
 #include <linux/rculist_nulls.h>
 #include <linux/cpu.h>
 #include <linux/tracehook.h>
-#include <linux/freezer.h>
 
 #include "../kernel/sched/sched.h"
 #include "io-wq.h"
@@ -503,10 +502,16 @@ static int io_wqe_worker(void *data)
 		if (io_flush_signals())
 			continue;
 		ret = schedule_timeout(WORKER_IDLE_TIMEOUT);
-		if (try_to_freeze() || ret)
+		if (signal_pending(current)) {
+			struct ksignal ksig;
+
+			if (fatal_signal_pending(current))
+				break;
+			if (get_signal(&ksig))
+				continue;
+		}
+		if (ret)
 			continue;
-		if (fatal_signal_pending(current))
-			break;
 		/* timed out, exit unless we're the fixed worker */
 		if (test_bit(IO_WQ_BIT_EXIT, &wq->state) ||
 		    !(worker->flags & IO_WORKER_F_FIXED))
@@ -714,9 +719,14 @@ static int io_wq_manager(void *data)
 		set_current_state(TASK_INTERRUPTIBLE);
 		io_wq_check_workers(wq);
 		schedule_timeout(HZ);
-		try_to_freeze();
-		if (fatal_signal_pending(current))
-			set_bit(IO_WQ_BIT_EXIT, &wq->state);
+		if (signal_pending(current)) {
+			struct ksignal ksig;
+
+			if (fatal_signal_pending(current))
+				set_bit(IO_WQ_BIT_EXIT, &wq->state);
+			else if (get_signal(&ksig))
+				continue;
+		}
 	} while (!test_bit(IO_WQ_BIT_EXIT, &wq->state));
 
 	io_wq_check_workers(wq);
diff --git a/fs/io_uring.c b/fs/io_uring.c
index 54ea561db4a5..350418a88db3 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -78,7 +78,6 @@
 #include <linux/task_work.h>
 #include <linux/pagemap.h>
 #include <linux/io_uring.h>
-#include <linux/freezer.h>
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/io_uring.h>
@@ -6765,8 +6764,14 @@ static int io_sq_thread(void *data)
 			timeout = jiffies + sqd->sq_thread_idle;
 			continue;
 		}
-		if (fatal_signal_pending(current))
-			break;
+		if (signal_pending(current)) {
+			struct ksignal ksig;
+
+			if (fatal_signal_pending(current))
+				break;
+			if (get_signal(&ksig))
+				continue;
+		}
 		sqt_spin = false;
 		cap_entries = !list_is_singular(&sqd->ctx_list);
 		list_for_each_entry(ctx, &sqd->ctx_list, sqd_list) {
@@ -6809,7 +6814,6 @@ static int io_sq_thread(void *data)
 
 			mutex_unlock(&sqd->lock);
 			schedule();
-			try_to_freeze();
 			mutex_lock(&sqd->lock);
 			list_for_each_entry(ctx, &sqd->ctx_list, sqd_list)
 				io_ring_clear_wakeup_flag(ctx);
-- 
2.31.0