linux-kernel - Re: [PATCH v2 1/2] io_uring: Add new functions to handle user fault scenarios

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Message-ID: <52d55891-36e3-43e7-9726-a2cd113f5327@kernel.dk>
Date: Wed, 23 Apr 2025 09:55:04 -0600
From: Jens Axboe <axboe@...nel.dk>
To: 姜智伟 <qq282012236@...il.com>
Cc: viro@...iv.linux.org.uk, brauner@...nel.org, jack@...e.cz,
 akpm@...ux-foundation.org, peterx@...hat.com, asml.silence@...il.com,
 linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, io-uring@...r.kernel.org
Subject: Re: [PATCH v2 1/2] io_uring: Add new functions to handle user fault
 scenarios

Something like this, perhaps - it'll ensure that io-wq workers get a
chance to flush out pending work, which should prevent the looping. I've
attached a basic test case. It'll issue a write that will fault, and
then try and cancel that as a way to trigger the TIF_NOTIFY_SIGNAL based
looping.

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index d80f94346199..e18926dbf20a 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -32,6 +32,7 @@
 #include <linux/swapops.h>
 #include <linux/miscdevice.h>
 #include <linux/uio.h>
+#include <linux/io_uring.h>
 
 static int sysctl_unprivileged_userfaultfd __read_mostly;
 
@@ -376,6 +377,8 @@ vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason)
 	 */
 	if (current->flags & (PF_EXITING|PF_DUMPCORE))
 		goto out;
+	else if (current->flags & PF_IO_WORKER)
+		io_worker_fault();
 
 	assert_fault_locked(vmf);
 
diff --git a/include/linux/io_uring.h b/include/linux/io_uring.h
index 85fe4e6b275c..d93dd7402a28 100644
--- a/include/linux/io_uring.h
+++ b/include/linux/io_uring.h
@@ -28,6 +28,7 @@ static inline void io_uring_free(struct task_struct *tsk)
 	if (tsk->io_uring)
 		__io_uring_free(tsk);
 }
+void io_worker_fault(void);
 #else
 static inline void io_uring_task_cancel(void)
 {
@@ -46,6 +47,9 @@ static inline bool io_is_uring_fops(struct file *file)
 {
 	return false;
 }
+static inline void io_worker_fault(void)
+{
+}
 #endif
 
 #endif
diff --git a/io_uring/io-wq.c b/io_uring/io-wq.c
index d52069b1177b..f74bea028ec7 100644
--- a/io_uring/io-wq.c
+++ b/io_uring/io-wq.c
@@ -1438,3 +1438,13 @@ static __init int io_wq_init(void)
 	return 0;
 }
 subsys_initcall(io_wq_init);
+
+void io_worker_fault(void)
+{
+	if (test_thread_flag(TIF_NOTIFY_SIGNAL))
+		clear_notify_signal();
+	if (test_thread_flag(TIF_NOTIFY_RESUME))
+		resume_user_mode_work(NULL);
+	if (task_work_pending(current))
+		task_work_run();
+}

-- 
Jens Axboe
View attachment "ufd.c" of type "text/x-csrc" (3324 bytes)