Merge tag 'io_uring-6.7-2023-11-17' of git://git.kernel.dk/linux

Pull io_uring fix from Jens Axboe:
 "Just a single fixup for a change we made in this release, which caused
  a regression in sometimes missing fdinfo output if the SQPOLL thread
  had the lock held when fdinfo output was retrieved.

  This brings us back on par with what we had before, where just the
  main uring_lock will prevent that output. We'd love to get rid of that
  too, but that is beyond the scope of this release and will have to
  wait for 6.8"

* tag 'io_uring-6.7-2023-11-17' of git://git.kernel.dk/linux:
  io_uring/fdinfo: remove need for sqpoll lock for thread/pid retrieval

Author: torvalds

io_uring/fdinfo.c

@@ -145,13 +145,8 @@ __cold void io_uring_show_fdinfo(struct seq_file *m, struct file *f)
 	if (has_lock && (ctx->flags & IORING_SETUP_SQPOLL)) {
 		struct io_sq_data *sq = ctx->sq_data;
 
-		if (mutex_trylock(&sq->lock)) {
-			if (sq->thread) {
-				sq_pid = task_pid_nr(sq->thread);
-				sq_cpu = task_cpu(sq->thread);
-			}
-			mutex_unlock(&sq->lock);
-		}
+		sq_pid = sq->task_pid;
+		sq_cpu = sq->sq_cpu;
 	}
 
 	seq_printf(m, "SqThread:\t%d\n", sq_pid);

io_uring/sqpoll.c

@@ -214,6 +214,7 @@ static bool io_sqd_handle_event(struct io_sq_data *sqd)
 			did_sig = get_signal(&ksig);
 		cond_resched();
 		mutex_lock(&sqd->lock);
+		sqd->sq_cpu = raw_smp_processor_id();
 	}
 	return did_sig || test_bit(IO_SQ_THREAD_SHOULD_STOP, &sqd->state);
 }
@@ -229,10 +230,15 @@ static int io_sq_thread(void *data)
 	snprintf(buf, sizeof(buf), "iou-sqp-%d", sqd->task_pid);
 	set_task_comm(current, buf);
 
-	if (sqd->sq_cpu != -1)
+	/* reset to our pid after we've set task_comm, for fdinfo */
+	sqd->task_pid = current->pid;
+
+	if (sqd->sq_cpu != -1) {
 		set_cpus_allowed_ptr(current, cpumask_of(sqd->sq_cpu));
-	else
+	} else {
 		set_cpus_allowed_ptr(current, cpu_online_mask);
+		sqd->sq_cpu = raw_smp_processor_id();
+	}
 
 	mutex_lock(&sqd->lock);
 	while (1) {
@@ -261,6 +267,7 @@ static int io_sq_thread(void *data)
 				mutex_unlock(&sqd->lock);
 				cond_resched();
 				mutex_lock(&sqd->lock);
+				sqd->sq_cpu = raw_smp_processor_id();
 			}
 			continue;
 		}
@@ -294,6 +301,7 @@ static int io_sq_thread(void *data)
 				mutex_unlock(&sqd->lock);
 				schedule();
 				mutex_lock(&sqd->lock);
+				sqd->sq_cpu = raw_smp_processor_id();
 			}
 			list_for_each_entry(ctx, &sqd->ctx_list, sqd_list)
 				atomic_andnot(IORING_SQ_NEED_WAKEUP,