WARNING in __might_sleep (2)

WARNING in __might_sleep (2)

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    8fe28cb58bcb Linux 4.20
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16211a3b400000
kernel config:  https://syzkaller.appspot.com/x/.config?x=7d581260bae0899a
dashboard link: https://syzkaller.appspot.com/bug?extid=c244af085a0159d22879
compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1617cd8b400000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=11f5089b400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+c244af085a0159d22879@syzkaller.appspotmail.com

audit: type=1800 audit(1545700018.193:29): pid=7508 uid=0 auid=4294967295  
ses=4294967295 subj==unconfined op=collect_data cause=failed(directio)  
comm="startpar" name="rc.local" dev="sda1" ino=2432 res=0
------------[ cut here ]------------
do not call blocking ops when !TASK_RUNNING; state=1 set at  
[<000000004df58f46>] n_hdlc_tty_read+0x301/0x7f0 drivers/tty/n_hdlc.c:589
WARNING: CPU: 0 PID: 7659 at kernel/sched/core.c:6099  
__might_sleep+0x13d/0x190 kernel/sched/core.c:6094
Kernel panic - not syncing: panic_on_warn set ...
CPU: 0 PID: 7659 Comm: syz-executor111 Not tainted 4.20.0 #387
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Call Trace:
  __dump_stack lib/dump_stack.c:77 [inline]
  dump_stack+0x1d3/0x2c6 lib/dump_stack.c:113
  panic+0x2ad/0x55c kernel/panic.c:188
  __warn.cold.8+0x20/0x45 kernel/panic.c:540
  report_bug+0x254/0x2d0 lib/bug.c:186
  fixup_bug arch/x86/kernel/traps.c:178 [inline]
  do_error_trap+0x11b/0x200 arch/x86/kernel/traps.c:271
  do_invalid_op+0x36/0x40 arch/x86/kernel/traps.c:290
  invalid_op+0x14/0x20 arch/x86/entry/entry_64.S:973
RIP: 0010:__might_sleep+0x13d/0x190 kernel/sched/core.c:6094
Code: 65 48 8b 1c 25 40 ee 01 00 48 8d 7b 10 48 89 fe 48 c1 ee 03 80 3c 06  
00 75 2b 48 8b 73 10 48 c7 c7 40 e0 2a 88 e8 43 27 f3 ff <0f> 0b e9 43 ff  
ff ff e8 f7 7c 6c 00 e9 26 ff ff ff e8 ed 7c 6c 00
RSP: 0018:ffff8881b8db7948 EFLAGS: 00010286
RAX: 0000000000000000 RBX: ffff8881b8cae6c0 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff8164e045 RDI: 0000000000000005
RBP: ffff8881b8db7978 R08: ffff8881b8cae6c0 R09: 0000000000000007
R10: 0000000000000000 R11: ffff8881b8cae6c0 R12: ffffffff8860b220
R13: 0000000000000019 R14: 0000000000000000 R15: ffff8881b8cae6c0
  __might_fault+0xc6/0x1e0 mm/memory.c:4357
  _copy_to_user+0x30/0x110 lib/usercopy.c:25
  copy_to_user include/linux/uaccess.h:155 [inline]
  n_hdlc_tty_read+0x5c1/0x7f0 drivers/tty/n_hdlc.c:600
  tty_read+0x194/0x2a0 drivers/tty/tty_io.c:866
  __vfs_read+0x117/0x9b0 fs/read_write.c:416
  vfs_read+0x17f/0x3c0 fs/read_write.c:452
  ksys_read+0x101/0x260 fs/read_write.c:578
  __do_sys_read fs/read_write.c:588 [inline]
  __se_sys_read fs/read_write.c:586 [inline]
  __x64_sys_read+0x73/0xb0 fs/read_write.c:586
  do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
  entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x440099
Code: 18 89 d0 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 48 89 f8 48 89 f7  
48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff  
ff 0f 83 fb 13 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffeeb4e9ec8 EFLAGS: 00000207 ORIG_RAX: 0000000000000000
RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 0000000000440099
RDX: 0000000000000057 RSI: 0000000020000080 RDI: 0000000000000003
RBP: 00000000006ca018 R08: 00000000004002c8 R09: 00000000004002c8
R10: 00000000004002c8 R11: 0000000000000207 R12: 0000000000401920
R13: 00000000004019b0 R14: 0000000000000000 R15: 0000000000000000
Kernel Offset: disabled
Rebooting in 86400 seconds..


---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@googlegroups.com.

syzbot will keep track of this bug report. See:
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syzbot can test patches for this bug, for details see:
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[PATCH] tty/n_hdlc: fix sleep in !TASK_RUNNING state warning

[Tetsuo Handa]

syzbot is hitting __might_sleep() warning [1], for commit 1035b63d3c6fc34a
("n_hdlc: fix read and write locking") changed to set TASK_INTERRUPTIBLE
state before calling copy_to_user(). Let's set TASK_INTERRUPTIBLE state
immediately before calling schedule().

[1] https://syzkaller.appspot.com/bug?id=17d5de7f1fcab794cb8c40032f893f52de899324

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Reported-by: syzbot <syzbot+c244af085a0159d22879@syzkaller.appspotmail.com>
Cc: Paul Fulghum <paulkf@microgate.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
---
 drivers/tty/n_hdlc.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/drivers/tty/n_hdlc.c b/drivers/tty/n_hdlc.c
index dabb391..7835489 100644
--- a/drivers/tty/n_hdlc.c
+++ b/drivers/tty/n_hdlc.c
@@ -589,8 +589,6 @@ static ssize_t n_hdlc_tty_read(struct tty_struct *tty, struct file *file,
 		if (tty_hung_up_p(file))
 			break;
 
-		set_current_state(TASK_INTERRUPTIBLE);
-
 		rbuf = n_hdlc_buf_get(&n_hdlc->rx_buf_list);
 		if (rbuf) {
 			if (rbuf->count > nr) {
@@ -617,6 +615,7 @@ static ssize_t n_hdlc_tty_read(struct tty_struct *tty, struct file *file,
 			break;
 		}
 
+		set_current_state(TASK_INTERRUPTIBLE);
 		schedule();
 
 		if (signal_pending(current)) {
@@ -673,8 +672,6 @@ static ssize_t n_hdlc_tty_write(struct tty_struct *tty, struct file *file,
 	add_wait_queue(&tty->write_wait, &wait);
 
 	for (;;) {
-		set_current_state(TASK_INTERRUPTIBLE);
-	
 		tbuf = n_hdlc_buf_get(&n_hdlc->tx_free_buf_list);
 		if (tbuf)
 			break;
@@ -683,6 +680,8 @@ static ssize_t n_hdlc_tty_write(struct tty_struct *tty, struct file *file,
 			error = -EAGAIN;
 			break;
 		}
+
+		set_current_state(TASK_INTERRUPTIBLE);
 		schedule();
 			
 		n_hdlc = tty2n_hdlc (tty);
-- 
1.8.3.1

Re: [PATCH] tty/n_hdlc: fix sleep in !TASK_RUNNING state warning

[Paul Fulghum]

On Dec 31, 2018, at 7:11 PM, Paul Fulghum <paulkf@microgate.com> wrote:

NAK to this patch. It causes lost wakeups in both read and write paths.

The write path does not need changing.

The read path can be fixed by setting current to TASK_RUNNING at the top of the if (rbuf) block so the warning is not triggered by copy_to_user(). If this block runs the condition is satisfied and it breaks out of the polling loop where it is already being set to TASK_RUNNING and removed from the wait queue. This particular path just needs to account for the copy_to_user which occurs before breaking out.

I’ll make a patch to do this when I have the ability to test it in a day or two.


> On Dec 29, 2018, at 3:48 AM, Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> wrote:
> 
> syzbot is hitting __might_sleep() warning [1], for commit 1035b63d3c6fc34a
> ("n_hdlc: fix read and write locking") changed to set TASK_INTERRUPTIBLE
> state before calling copy_to_user(). Let's set TASK_INTERRUPTIBLE state
> immediately before calling schedule().
> 
> [1] https://syzkaller.appspot.com/bug?id=17d5de7f1fcab794cb8c40032f893f52de899324
> 
> Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> Reported-by: syzbot <syzbot+c244af085a0159d22879@syzkaller.appspotmail.com>
> Cc: Paul Fulghum <paulkf@microgate.com>
> Cc: Arnd Bergmann <arnd@arndb.de>
> Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
> ---
> drivers/tty/n_hdlc.c | 7 +++----
> 1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/tty/n_hdlc.c b/drivers/tty/n_hdlc.c
> index dabb391..7835489 100644
> --- a/drivers/tty/n_hdlc.c
> +++ b/drivers/tty/n_hdlc.c
> @@ -589,8 +589,6 @@ static ssize_t n_hdlc_tty_read(struct tty_struct *tty, struct file *file,
> 		if (tty_hung_up_p(file))
> 			break;
> 
> -		set_current_state(TASK_INTERRUPTIBLE);
> -
> 		rbuf = n_hdlc_buf_get(&n_hdlc->rx_buf_list);
> 		if (rbuf) {
> 			if (rbuf->count > nr) {
> @@ -617,6 +615,7 @@ static ssize_t n_hdlc_tty_read(struct tty_struct *tty, struct file *file,
> 			break;
> 		}
> 
> +		set_current_state(TASK_INTERRUPTIBLE);
> 		schedule();
> 
> 		if (signal_pending(current)) {
> @@ -673,8 +672,6 @@ static ssize_t n_hdlc_tty_write(struct tty_struct *tty, struct file *file,
> 	add_wait_queue(&tty->write_wait, &wait);
> 
> 	for (;;) {
> -		set_current_state(TASK_INTERRUPTIBLE);
> -	
> 		tbuf = n_hdlc_buf_get(&n_hdlc->tx_free_buf_list);
> 		if (tbuf)
> 			break;
> @@ -683,6 +680,8 @@ static ssize_t n_hdlc_tty_write(struct tty_struct *tty, struct file *file,
> 			error = -EAGAIN;
> 			break;
> 		}
> +
> +		set_current_state(TASK_INTERRUPTIBLE);
> 		schedule();
> 			
> 		n_hdlc = tty2n_hdlc (tty);
> -- 
> 1.8.3.1
> 
> 

--
Paul Fulghum
MicroGate Systems, Ltd.
=Customer Driven, by Design=
(512) 345-7791 x102 (Voice)
(512) 343-9046 (Fax)
Central Time Zone (GMT -5h)
www.microgate.com

[PATCH] tty/n_hdlc: fix __might_sleep warning

[Paul Fulghum]

Fix __might_sleep warning in tty/n_hdlc.c read due to copy_to_user call while current is TASK_INTERRUPTIBLE.
This is a false positive since the code path does not depend on current state remaining TASK_INTERRUPTIBLE.
The loop breaks out and sets TASK_RUNNING after calling copy_to_user. 
This patch supresses the warning by setting TASK_RUNNING before calling copy_to_user.

[1] https://syzkaller.appspot.com/bug?id=17d5de7f1fcab794cb8c40032f893f52de899324

Signed-off-by: Paul Fulghum <paulkf@microgate.com>
Reported-by: syzbot <syzbot+c244af085a0159d22879@syzkaller.appspotmail.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
—
--- a/drivers/tty/n_hdlc.c	2018-12-23 15:55:59.000000000 -0800
+++ b/drivers/tty/n_hdlc.c	2019-01-01 11:44:47.148153954 -0800
@@ -597,6 +597,7 @@ static ssize_t n_hdlc_tty_read(struct tt
 				/* too large for caller's buffer */
 				ret = -EOVERFLOW;
 			} else {
+				__set_current_state(TASK_RUNNING);
 				if (copy_to_user(buf, rbuf->buf, rbuf->count))
 					ret = -EFAULT;
 				else

 

Re: [PATCH] tty/n_hdlc: fix sleep in !TASK_RUNNING state warning

[Tetsuo Handa]

On 2019/01/01 12:11, Paul Fulghum wrote:
> NAK to this patch. It causes lost wakeups in both read and write paths.
> 
> The write path does not need changing.
> 
> The read path can be fixed by setting current to TASK_RUNNING at the top of the if (rbuf) block
> so the warning is not triggered by copy_to_user(). If this block runs the condition is satisfied
> and it breaks out of the polling loop where it is already being set to TASK_RUNNING and removed
> from the wait queue. This particular path just needs to account for the copy_to_user which occurs
> before breaking out.
> 
> I’ll make a patch to do this when I have the ability to test it in a day or two.
> 

OK. Then, any chance it is rewritten using wait_event_interruptible() in order to reduce lines?
( wait_event_interruptible() automatically calls might_sleep(), but is it acceptable for you? )

---
 drivers/tty/n_hdlc.c | 126 ++++++++++++---------------------------------------
 1 file changed, 30 insertions(+), 96 deletions(-)

diff --git a/drivers/tty/n_hdlc.c b/drivers/tty/n_hdlc.c
index 8223d02..2e4ccf9 100644
--- a/drivers/tty/n_hdlc.c
+++ b/drivers/tty/n_hdlc.c
@@ -562,8 +562,7 @@ static ssize_t n_hdlc_tty_read(struct tty_struct *tty, struct file *file,
 {
 	struct n_hdlc *n_hdlc = tty2n_hdlc(tty);
 	int ret = 0;
-	struct n_hdlc_buf *rbuf;
-	DECLARE_WAITQUEUE(wait, current);
+	struct n_hdlc_buf *rbuf = NULL;
 
 	if (debuglevel >= DEBUG_LEVEL_INFO)	
 		printk("%s(%d)n_hdlc_tty_read() called\n",__FILE__,__LINE__);
@@ -579,58 +578,26 @@ static ssize_t n_hdlc_tty_read(struct tty_struct *tty, struct file *file,
 		return -EFAULT;
 	}
 
-	add_wait_queue(&tty->read_wait, &wait);
-
-	for (;;) {
-		if (test_bit(TTY_OTHER_CLOSED, &tty->flags)) {
-			ret = -EIO;
-			break;
-		}
-		if (tty_hung_up_p(file))
-			break;
-
-		set_current_state(TASK_INTERRUPTIBLE);
-
-		rbuf = n_hdlc_buf_get(&n_hdlc->rx_buf_list);
-		if (rbuf) {
-			if (rbuf->count > nr) {
-				/* too large for caller's buffer */
-				ret = -EOVERFLOW;
-			} else {
-				__set_current_state(TASK_RUNNING);
-				if (copy_to_user(buf, rbuf->buf, rbuf->count))
-					ret = -EFAULT;
-				else
-					ret = rbuf->count;
-			}
-
-			if (n_hdlc->rx_free_buf_list.count >
-			    DEFAULT_RX_BUF_COUNT)
-				kfree(rbuf);
-			else
-				n_hdlc_buf_put(&n_hdlc->rx_free_buf_list, rbuf);
-			break;
-		}
-			
-		/* no data */
-		if (tty_io_nonblock(tty, file)) {
-			ret = -EAGAIN;
-			break;
-		}
-
-		schedule();
-
-		if (signal_pending(current)) {
-			ret = -EINTR;
-			break;
-		}
+	if (wait_event_interruptible(tty->read_wait,
+	     (ret = -EIO, test_bit(TTY_OTHER_CLOSED, &tty->flags)) ||
+	     (ret = 0, tty_hung_up_p(file)) ||
+	     (rbuf = n_hdlc_buf_get(&n_hdlc->rx_buf_list)) != NULL ||
+	     (ret = -EAGAIN, tty_io_nonblock(tty, file))))
+		return -EINTR;
+	if (rbuf) {
+		if (rbuf->count > nr)
+			/* too large for caller's buffer */
+			ret = -EOVERFLOW;
+		else if (copy_to_user(buf, rbuf->buf, rbuf->count))
+			ret = -EFAULT;
+		else
+			ret = rbuf->count;
+		if (n_hdlc->rx_free_buf_list.count > DEFAULT_RX_BUF_COUNT)
+			kfree(rbuf);
+		else
+			n_hdlc_buf_put(&n_hdlc->rx_free_buf_list, rbuf);
 	}
-
-	remove_wait_queue(&tty->read_wait, &wait);
-	__set_current_state(TASK_RUNNING);
-
 	return ret;
-	
 }	/* end of n_hdlc_tty_read() */
 
 /**
@@ -645,21 +612,13 @@ static ssize_t n_hdlc_tty_read(struct tty_struct *tty, struct file *file,
 static ssize_t n_hdlc_tty_write(struct tty_struct *tty, struct file *file,
 			    const unsigned char *data, size_t count)
 {
-	struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
+	struct n_hdlc *n_hdlc;
 	int error = 0;
-	DECLARE_WAITQUEUE(wait, current);
-	struct n_hdlc_buf *tbuf;
+	struct n_hdlc_buf *tbuf = NULL;
 
 	if (debuglevel >= DEBUG_LEVEL_INFO)	
 		printk("%s(%d)n_hdlc_tty_write() called count=%zd\n",
 			__FILE__,__LINE__,count);
-		
-	/* Verify pointers */
-	if (!n_hdlc)
-		return -EIO;
-
-	if (n_hdlc->magic != HDLC_MAGIC)
-		return -EIO;
 
 	/* verify frame size */
 	if (count > maxframe ) {
@@ -670,40 +629,14 @@ static ssize_t n_hdlc_tty_write(struct tty_struct *tty, struct file *file,
 				maxframe );
 		count = maxframe;
 	}
-	
-	add_wait_queue(&tty->write_wait, &wait);
 
-	for (;;) {
-		set_current_state(TASK_INTERRUPTIBLE);
-	
-		tbuf = n_hdlc_buf_get(&n_hdlc->tx_free_buf_list);
-		if (tbuf)
-			break;
-
-		if (tty_io_nonblock(tty, file)) {
-			error = -EAGAIN;
-			break;
-		}
-		schedule();
-			
-		n_hdlc = tty2n_hdlc (tty);
-		if (!n_hdlc || n_hdlc->magic != HDLC_MAGIC || 
-		    tty != n_hdlc->tty) {
-			printk("n_hdlc_tty_write: %p invalid after wait!\n", n_hdlc);
-			error = -EIO;
-			break;
-		}
-			
-		if (signal_pending(current)) {
-			error = -EINTR;
-			break;
-		}
-	}
-
-	__set_current_state(TASK_RUNNING);
-	remove_wait_queue(&tty->write_wait, &wait);
-
-	if (!error) {		
+	if (wait_event_interruptible(tty->write_wait,
+	     (error = -EIO, n_hdlc = tty2n_hdlc(tty), /* Verify pointers */
+	      !n_hdlc || n_hdlc->magic != HDLC_MAGIC || tty != n_hdlc->tty) ||
+	     (tbuf = n_hdlc_buf_get(&n_hdlc->tx_free_buf_list)) != NULL ||
+	     (error = -EAGAIN, tty_io_nonblock(tty, file))))
+		return -EINTR;
+	if (tbuf) {
 		/* Retrieve the user's buffer */
 		memcpy(tbuf->buf, data, count);
 
@@ -711,8 +644,9 @@ static ssize_t n_hdlc_tty_write(struct tty_struct *tty, struct file *file,
 		tbuf->count = error = count;
 		n_hdlc_buf_put(&n_hdlc->tx_buf_list,tbuf);
 		n_hdlc_send_frames(n_hdlc,tty);
+	} else if (error == -EIO) {
+		printk("n_hdlc_tty_write: %p invalid!\n", n_hdlc);
 	}
-
 	return error;
 	
 }	/* end of n_hdlc_tty_write() */
-- 
1.8.3.1

Re: [PATCH] tty/n_hdlc: fix sleep in !TASK_RUNNING state warning

[Paul Fulghum]

> On Jan 2, 2019, at 7:04 AM, Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> wrote:
> 
> On 2019/01/01 12:11, Paul Fulghum wrote:
>> NAK to this patch. It causes lost wakeups in both read and write paths.
>> 
>> The write path does not need changing.
>> 
>> The read path can be fixed by setting current to TASK_RUNNING at the top of the if (rbuf) block
>> so the warning is not triggered by copy_to_user(). If this block runs the condition is satisfied
>> and it breaks out of the polling loop where it is already being set to TASK_RUNNING and removed
>> from the wait queue. This particular path just needs to account for the copy_to_user which occurs
>> before breaking out.
>> 
>> I’ll make a patch to do this when I have the ability to test it in a day or two.
>> 
> 
> OK. Then, any chance it is rewritten using wait_event_interruptible() in order to reduce lines?
> ( wait_event_interruptible() automatically calls might_sleep(), but is it acceptable for you? )
> 

This looks good to me. I applied it and tested blocking (sleep/no sleep) and non-blocking (success/EAGAIN) paths for both read and write.

Re: [PATCH] tty/n_hdlc: fix sleep in !TASK_RUNNING state warning

[Jiri Slaby]

On 02. 01. 19, 16:04, Tetsuo Handa wrote:
> +	if (wait_event_interruptible(tty->read_wait,
> +	     (ret = -EIO, test_bit(TTY_OTHER_CLOSED, &tty->flags)) ||
> +	     (ret = 0, tty_hung_up_p(file)) ||
> +	     (rbuf = n_hdlc_buf_get(&n_hdlc->rx_buf_list)) != NULL ||
> +	     (ret = -EAGAIN, tty_io_nonblock(tty, file))))
> +		return -EINTR;

Oh, that looks really ugly. Could you move all this to a function
returning a bool and taking &ret and &rbuf as parameters?

> +	if (rbuf) {
> +		if (rbuf->count > nr)
> +			/* too large for caller's buffer */
> +			ret = -EOVERFLOW;
> +		else if (copy_to_user(buf, rbuf->buf, rbuf->count))
> +			ret = -EFAULT;
> +		else
> +			ret = rbuf->count;
> +		if (n_hdlc->rx_free_buf_list.count > DEFAULT_RX_BUF_COUNT)
> +			kfree(rbuf);
> +		else
> +			n_hdlc_buf_put(&n_hdlc->rx_free_buf_list, rbuf);
>  	}
> -
> -	remove_wait_queue(&tty->read_wait, &wait);
> -	__set_current_state(TASK_RUNNING);
> -
>  	return ret;
> -	
>  }	/* end of n_hdlc_tty_read() */
>  
>  /**
> @@ -645,21 +612,13 @@ static ssize_t n_hdlc_tty_read(struct tty_struct *tty, struct file *file,
>  static ssize_t n_hdlc_tty_write(struct tty_struct *tty, struct file *file,
>  			    const unsigned char *data, size_t count)
>  {
> -	struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
> +	struct n_hdlc *n_hdlc;
>  	int error = 0;
> -	DECLARE_WAITQUEUE(wait, current);
> -	struct n_hdlc_buf *tbuf;
> +	struct n_hdlc_buf *tbuf = NULL;
>  
>  	if (debuglevel >= DEBUG_LEVEL_INFO)	
>  		printk("%s(%d)n_hdlc_tty_write() called count=%zd\n",
>  			__FILE__,__LINE__,count);
> -		
> -	/* Verify pointers */
> -	if (!n_hdlc)
> -		return -EIO;
> -
> -	if (n_hdlc->magic != HDLC_MAGIC)
> -		return -EIO;
>  
>  	/* verify frame size */
>  	if (count > maxframe ) {
> @@ -670,40 +629,14 @@ static ssize_t n_hdlc_tty_write(struct tty_struct *tty, struct file *file,
>  				maxframe );
>  		count = maxframe;
>  	}
> -	
> -	add_wait_queue(&tty->write_wait, &wait);
>  
> -	for (;;) {
> -		set_current_state(TASK_INTERRUPTIBLE);
> -	
> -		tbuf = n_hdlc_buf_get(&n_hdlc->tx_free_buf_list);
> -		if (tbuf)
> -			break;
> -
> -		if (tty_io_nonblock(tty, file)) {
> -			error = -EAGAIN;
> -			break;
> -		}
> -		schedule();
> -			
> -		n_hdlc = tty2n_hdlc (tty);
> -		if (!n_hdlc || n_hdlc->magic != HDLC_MAGIC || 
> -		    tty != n_hdlc->tty) {
> -			printk("n_hdlc_tty_write: %p invalid after wait!\n", n_hdlc);
> -			error = -EIO;
> -			break;
> -		}
> -			
> -		if (signal_pending(current)) {
> -			error = -EINTR;
> -			break;
> -		}
> -	}
> -
> -	__set_current_state(TASK_RUNNING);
> -	remove_wait_queue(&tty->write_wait, &wait);
> -
> -	if (!error) {		
> +	if (wait_event_interruptible(tty->write_wait,
> +	     (error = -EIO, n_hdlc = tty2n_hdlc(tty), /* Verify pointers */
> +	      !n_hdlc || n_hdlc->magic != HDLC_MAGIC || tty != n_hdlc->tty) ||
> +	     (tbuf = n_hdlc_buf_get(&n_hdlc->tx_free_buf_list)) != NULL ||
> +	     (error = -EAGAIN, tty_io_nonblock(tty, file))))
> +		return -EINTR;

This is even worse. So detto as above?

> +	if (tbuf) {
>  		/* Retrieve the user's buffer */
>  		memcpy(tbuf->buf, data, count);
>  
> @@ -711,8 +644,9 @@ static ssize_t n_hdlc_tty_write(struct tty_struct *tty, struct file *file,
>  		tbuf->count = error = count;
>  		n_hdlc_buf_put(&n_hdlc->tx_buf_list,tbuf);
>  		n_hdlc_send_frames(n_hdlc,tty);
> +	} else if (error == -EIO) {
> +		printk("n_hdlc_tty_write: %p invalid!\n", n_hdlc);
>  	}
> -
>  	return error;
>  	
>  }	/* end of n_hdlc_tty_write() */
> 

thanks,
-- 
js
suse labs

Re: [PATCH] tty/n_hdlc: fix sleep in !TASK_RUNNING state warning

[Tetsuo Handa]

On 2019/01/03 18:09, Jiri Slaby wrote:
> On 02. 01. 19, 16:04, Tetsuo Handa wrote:
>> +	if (wait_event_interruptible(tty->read_wait,
>> +	     (ret = -EIO, test_bit(TTY_OTHER_CLOSED, &tty->flags)) ||
>> +	     (ret = 0, tty_hung_up_p(file)) ||
>> +	     (rbuf = n_hdlc_buf_get(&n_hdlc->rx_buf_list)) != NULL ||
>> +	     (ret = -EAGAIN, tty_io_nonblock(tty, file))))
>> +		return -EINTR;
> 
> Oh, that looks really ugly. Could you move all this to a function
> returning a bool and taking &ret and &rbuf as parameters?
> 

OK. Something like this?

From 725c55be437b6ce3b578a045cc7ddeeb2bbeb4b3 Mon Sep 17 00:00:00 2001
From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Date: Thu, 3 Jan 2019 20:29:49 +0900
Subject: [PATCH] tty/n_hdlc: Use wait_event_interruptible() and same sanity
 checks.

We can use wait_event_interruptible() in order to make it easier to
understand. Also, since the reason of using different level/frequency of
sanity checks for read and write is unclear while nowadays we have rich
fuzzing/sanitizing tools, let's use same sanity checks for read and write.

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
---
 drivers/tty/n_hdlc.c | 154 ++++++++++++++++++++-------------------------------
 1 file changed, 61 insertions(+), 93 deletions(-)

diff --git a/drivers/tty/n_hdlc.c b/drivers/tty/n_hdlc.c
index 8223d02..c497ef1 100644
--- a/drivers/tty/n_hdlc.c
+++ b/drivers/tty/n_hdlc.c
@@ -548,6 +548,27 @@ static void n_hdlc_tty_receive(struct tty_struct *tty, const __u8 *data,
 
 }	/* end of n_hdlc_tty_receive() */
 
+static bool __n_hdlc_tty_read(struct tty_struct *tty, struct file *file,
+			      struct n_hdlc *n_hdlc, int *ret,
+			      struct n_hdlc_buf **rbuf)
+{
+	if (test_bit(TTY_OTHER_CLOSED, &tty->flags)) {
+		*ret = -EIO;
+		return true;
+	}
+	if (tty_hung_up_p(file))
+		return true;
+	*rbuf = n_hdlc_buf_get(&n_hdlc->rx_buf_list);
+	if (*rbuf)
+		return true;
+	/* no data */
+	if (tty_io_nonblock(tty, file)) {
+		*ret = -EAGAIN;
+		return true;
+	}
+	return false;
+}
+
 /**
  * n_hdlc_tty_read - Called to retrieve one frame of data (if available)
  * @tty - pointer to tty instance data
@@ -562,14 +583,13 @@ static ssize_t n_hdlc_tty_read(struct tty_struct *tty, struct file *file,
 {
 	struct n_hdlc *n_hdlc = tty2n_hdlc(tty);
 	int ret = 0;
-	struct n_hdlc_buf *rbuf;
-	DECLARE_WAITQUEUE(wait, current);
+	struct n_hdlc_buf *rbuf = NULL;
 
 	if (debuglevel >= DEBUG_LEVEL_INFO)	
 		printk("%s(%d)n_hdlc_tty_read() called\n",__FILE__,__LINE__);
 		
 	/* Validate the pointers */
-	if (!n_hdlc)
+	if (!n_hdlc || n_hdlc->magic != HDLC_MAGIC)
 		return -EIO;
 
 	/* verify user access to buffer */
@@ -579,60 +599,41 @@ static ssize_t n_hdlc_tty_read(struct tty_struct *tty, struct file *file,
 		return -EFAULT;
 	}
 
-	add_wait_queue(&tty->read_wait, &wait);
-
-	for (;;) {
-		if (test_bit(TTY_OTHER_CLOSED, &tty->flags)) {
-			ret = -EIO;
-			break;
-		}
-		if (tty_hung_up_p(file))
-			break;
-
-		set_current_state(TASK_INTERRUPTIBLE);
-
-		rbuf = n_hdlc_buf_get(&n_hdlc->rx_buf_list);
-		if (rbuf) {
-			if (rbuf->count > nr) {
-				/* too large for caller's buffer */
-				ret = -EOVERFLOW;
-			} else {
-				__set_current_state(TASK_RUNNING);
-				if (copy_to_user(buf, rbuf->buf, rbuf->count))
-					ret = -EFAULT;
-				else
-					ret = rbuf->count;
-			}
-
-			if (n_hdlc->rx_free_buf_list.count >
-			    DEFAULT_RX_BUF_COUNT)
-				kfree(rbuf);
-			else
-				n_hdlc_buf_put(&n_hdlc->rx_free_buf_list, rbuf);
-			break;
-		}
-			
-		/* no data */
-		if (tty_io_nonblock(tty, file)) {
-			ret = -EAGAIN;
-			break;
-		}
-
-		schedule();
-
-		if (signal_pending(current)) {
-			ret = -EINTR;
-			break;
-		}
+	if (wait_event_interruptible(tty->read_wait,
+				     __n_hdlc_tty_read(tty, file, n_hdlc, &ret,
+						       &rbuf)))
+		return -EINTR;
+	if (rbuf) {
+		if (rbuf->count > nr)
+			/* too large for caller's buffer */
+			ret = -EOVERFLOW;
+		else if (copy_to_user(buf, rbuf->buf, rbuf->count))
+			ret = -EFAULT;
+		else
+			ret = rbuf->count;
+		if (n_hdlc->rx_free_buf_list.count > DEFAULT_RX_BUF_COUNT)
+			kfree(rbuf);
+		else
+			n_hdlc_buf_put(&n_hdlc->rx_free_buf_list, rbuf);
 	}
-
-	remove_wait_queue(&tty->read_wait, &wait);
-	__set_current_state(TASK_RUNNING);
-
 	return ret;
 	
 }	/* end of n_hdlc_tty_read() */
 
+static bool __n_hdlc_tty_write(struct tty_struct *tty, struct file *file,
+			       struct n_hdlc *n_hdlc, int *error,
+			       struct n_hdlc_buf **tbuf)
+{
+	*tbuf = n_hdlc_buf_get(&n_hdlc->tx_free_buf_list);
+	if (*tbuf)
+		return true;
+	if (tty_io_nonblock(tty, file)) {
+		*error = -EAGAIN;
+		return true;
+	}
+	return false;
+}
+
 /**
  * n_hdlc_tty_write - write a single frame of data to device
  * @tty	- pointer to associated tty device instance data
@@ -645,20 +646,16 @@ static ssize_t n_hdlc_tty_read(struct tty_struct *tty, struct file *file,
 static ssize_t n_hdlc_tty_write(struct tty_struct *tty, struct file *file,
 			    const unsigned char *data, size_t count)
 {
-	struct n_hdlc *n_hdlc = tty2n_hdlc (tty);
+	struct n_hdlc *n_hdlc = tty2n_hdlc(tty);
 	int error = 0;
-	DECLARE_WAITQUEUE(wait, current);
 	struct n_hdlc_buf *tbuf;
 
 	if (debuglevel >= DEBUG_LEVEL_INFO)	
 		printk("%s(%d)n_hdlc_tty_write() called count=%zd\n",
 			__FILE__,__LINE__,count);
-		
-	/* Verify pointers */
-	if (!n_hdlc)
-		return -EIO;
 
-	if (n_hdlc->magic != HDLC_MAGIC)
+	/* Validate the pointers */
+	if (!n_hdlc || n_hdlc->magic != HDLC_MAGIC)
 		return -EIO;
 
 	/* verify frame size */
@@ -670,40 +667,12 @@ static ssize_t n_hdlc_tty_write(struct tty_struct *tty, struct file *file,
 				maxframe );
 		count = maxframe;
 	}
-	
-	add_wait_queue(&tty->write_wait, &wait);
-
-	for (;;) {
-		set_current_state(TASK_INTERRUPTIBLE);
-	
-		tbuf = n_hdlc_buf_get(&n_hdlc->tx_free_buf_list);
-		if (tbuf)
-			break;
-
-		if (tty_io_nonblock(tty, file)) {
-			error = -EAGAIN;
-			break;
-		}
-		schedule();
-			
-		n_hdlc = tty2n_hdlc (tty);
-		if (!n_hdlc || n_hdlc->magic != HDLC_MAGIC || 
-		    tty != n_hdlc->tty) {
-			printk("n_hdlc_tty_write: %p invalid after wait!\n", n_hdlc);
-			error = -EIO;
-			break;
-		}
-			
-		if (signal_pending(current)) {
-			error = -EINTR;
-			break;
-		}
-	}
-
-	__set_current_state(TASK_RUNNING);
-	remove_wait_queue(&tty->write_wait, &wait);
 
-	if (!error) {		
+	if (wait_event_interruptible(tty->write_wait,
+				     __n_hdlc_tty_write(tty, file, n_hdlc,
+							&error, &tbuf)))
+		return -EINTR;
+	if (tbuf) {
 		/* Retrieve the user's buffer */
 		memcpy(tbuf->buf, data, count);
 
@@ -712,7 +681,6 @@ static ssize_t n_hdlc_tty_write(struct tty_struct *tty, struct file *file,
 		n_hdlc_buf_put(&n_hdlc->tx_buf_list,tbuf);
 		n_hdlc_send_frames(n_hdlc,tty);
 	}
-
 	return error;
 	
 }	/* end of n_hdlc_tty_write() */
-- 
1.8.3.1

Re: [PATCH] tty/n_hdlc: fix sleep in !TASK_RUNNING state warning

[Paul Fulghum]

> On Jan 3, 2019, at 3:32 AM, Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp> wrote:
> 
> On 2019/01/03 18:09, Jiri Slaby wrote:
>> On 02. 01. 19, 16:04, Tetsuo Handa wrote:
>>> +	if (wait_event_interruptible(tty->read_wait,
>>> +	     (ret = -EIO, test_bit(TTY_OTHER_CLOSED, &tty->flags)) ||
>>> +	     (ret = 0, tty_hung_up_p(file)) ||
>>> +	     (rbuf = n_hdlc_buf_get(&n_hdlc->rx_buf_list)) != NULL ||
>>> +	     (ret = -EAGAIN, tty_io_nonblock(tty, file))))
>>> +		return -EINTR;
>> 
>> Oh, that looks really ugly. Could you move all this to a function
>> returning a bool and taking &ret and &rbuf as parameters?
>> 
> 
> OK. Something like this?


I agree with Jiri that placing all the conditional logic in a single expression is difficult to read.

But exchanging that many locals with a separate function defeats the original purpose of
simplifying code and this implementation changes the logic (write no
longer checks for line discipline changing under it during wait).

Converting to wait_event_interruptible where possible is a good goal but this instance
may be better left alone. The current structure mirrors the existing n_tty line discipline.

Re: [PATCH] tty/n_hdlc: fix sleep in !TASK_RUNNING state warning

[Tetsuo Handa]

On 2019/01/04 0:57, Paul Fulghum wrote:
>> On Jan 3, 2019, at 3:32 AM, Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp> wrote:
>>
>> On 2019/01/03 18:09, Jiri Slaby wrote:
>>> On 02. 01. 19, 16:04, Tetsuo Handa wrote:
>>>> +	if (wait_event_interruptible(tty->read_wait,
>>>> +	     (ret = -EIO, test_bit(TTY_OTHER_CLOSED, &tty->flags)) ||
>>>> +	     (ret = 0, tty_hung_up_p(file)) ||
>>>> +	     (rbuf = n_hdlc_buf_get(&n_hdlc->rx_buf_list)) != NULL ||
>>>> +	     (ret = -EAGAIN, tty_io_nonblock(tty, file))))
>>>> +		return -EINTR;
>>>
>>> Oh, that looks really ugly. Could you move all this to a function
>>> returning a bool and taking &ret and &rbuf as parameters?
>>>
>>
>> OK. Something like this?
> 
> 
> I agree with Jiri that placing all the conditional logic in a single expression is difficult to read.
> 
> But exchanging that many locals with a separate function defeats the original purpose of
> simplifying code and this implementation changes the logic (write no
> longer checks for line discipline changing under it during wait).

Not only defeating the original purpose but also increasing object size.

> 
> Converting to wait_event_interruptible where possible is a good goal but this instance
> may be better left alone. The current structure mirrors the existing n_tty line discipline.

But why not to clarify what are appropriate sanity checks?

Currently, read side does not check "n_hdlc->magic != HDLC_MAGIC" case
while write side does. If it is intended for catching memory corruption
etc. then both sides should do the same thing.

Currently, write side does not check "tty != n_hdlc->tty" case before
schedule() while does after schedule(). If "tty != n_hdlc->tty" case
can ever happen, what prevents n_hdlc_tty_write() from being called again
after n_hdlc_tty_write() once returned with -EIO due to "tty != n_hdlc->tty"
case? If it is intended for catching memory corruption etc. then both
sides should check "tty != n_hdlc->tty" case.

Current logic is unclear, in addition to want a cleanup for scripts/checkpatch.pl .

  total: 158 errors, 95 warnings, 994 lines checked

Re: [PATCH] tty/n_hdlc: fix sleep in !TASK_RUNNING state warning

[Paul Fulghum]

> On Jan 4, 2019, at 2:23 AM, Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> wrote:
> 
> But why not to clarify what are appropriate sanity checks?
> ...
> want a cleanup for scripts/checkpatch.pl .


These are good goals. I avoid purely cosmetic patches. I do not object to cosmetic patches from others that do not change behavior.

The checks that concern you deal with changing tty line disciplines. Dealing with line discipline changes has been an ongoing issue since n_hdlc was derived from other line disciplines 20 years ago, with major overhauls along the way. It is complex: driver layers shifting during operation while dealing properly with opens, closes, hangups, and sleeping operations. Patches have been added to the latest unreleased kernel to address line discipline changes, it is still evolving.

Why are the existing line discipline checks in n_hdlc where they are? Becasue that’s how they evolved from where they started to accomodate these changes. There are not many and their function is known: has the line discipline changed at that point? I know that is not satisfying but coming up with a definitive comment saying a check is absolutely required in one place and not in another requires more insight into the long history of a moving target than I have. Without that insight I would not alter existing checks in code that is not causing problems.

Re: [PATCH] tty/n_hdlc: fix __might_sleep warning

[Tetsuo Handa]

Hello, Greg.

We attempted a cleanup but we failed. Thus, will you apply this patch for now?

On 2019/01/02 5:28, Paul Fulghum wrote:
> Fix __might_sleep warning in tty/n_hdlc.c read due to copy_to_user call while current is TASK_INTERRUPTIBLE.
> This is a false positive since the code path does not depend on current state remaining TASK_INTERRUPTIBLE.
> The loop breaks out and sets TASK_RUNNING after calling copy_to_user. 
> This patch supresses the warning by setting TASK_RUNNING before calling copy_to_user.
> 
> [1] https://syzkaller.appspot.com/bug?id=17d5de7f1fcab794cb8c40032f893f52de899324
> 
> Signed-off-by: Paul Fulghum <paulkf@microgate.com>
> Reported-by: syzbot <syzbot+c244af085a0159d22879@syzkaller.appspotmail.com>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> Cc: Arnd Bergmann <arnd@arndb.de>
> Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
> —
> --- a/drivers/tty/n_hdlc.c	2018-12-23 15:55:59.000000000 -0800
> +++ b/drivers/tty/n_hdlc.c	2019-01-01 11:44:47.148153954 -0800
> @@ -597,6 +597,7 @@ static ssize_t n_hdlc_tty_read(struct tt
>  				/* too large for caller's buffer */
>  				ret = -EOVERFLOW;
>  			} else {
> +				__set_current_state(TASK_RUNNING);
>  				if (copy_to_user(buf, rbuf->buf, rbuf->count))
>  					ret = -EFAULT;
>  				else

Re: [PATCH] tty/n_hdlc: fix __might_sleep warning

[Arnd Bergmann]

On Thu, Jan 10, 2019 at 12:39 PM Tetsuo Handa
<penguin-kernel@i-love.sakura.ne.jp> wrote:
> On 2019/01/02 5:28, Paul Fulghum wrote:
> > Fix __might_sleep warning in tty/n_hdlc.c read due to copy_to_user call while current is TASK_INTERRUPTIBLE.
> > This is a false positive since the code path does not depend on current state remaining TASK_INTERRUPTIBLE.
> > The loop breaks out and sets TASK_RUNNING after calling copy_to_user.
> > This patch supresses the warning by setting TASK_RUNNING before calling copy_to_user.
> >
> > [1] https://syzkaller.appspot.com/bug?id=17d5de7f1fcab794cb8c40032f893f52de899324
> >
> > Signed-off-by: Paul Fulghum <paulkf@microgate.com>
> > Reported-by: syzbot <syzbot+c244af085a0159d22879@syzkaller.appspotmail.com>
> > Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> > Cc: Arnd Bergmann <arnd@arndb.de>
> > Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>

This version looks good to me.

Acked-by: Arnd Bergmann <arnd@arndb.de>

       Arnd