4.9-stable review patch. If anyone has any objections, please let me know.
------------------
From: Oliver Neukum <oneukum@xxxxxxxx>
commit df3aa13c7bbb307e172c37f193f9a7aa058d4739 upstream.
This reverts commit a81cf9799ad7299b03a4dff020d9685f9ac5f3e0.
The patch causes a regression, which I cannot find the reason for.
So let's revert for now, as a revert hurts only performance.
Original report:
I was trying to resolve the problem with Oliver but we don't get any conclusion
for 5 months, so I am now sending this to mail list and cdc_acm authors.
I am using simple request-response protocol to obtain the boiller parameters
in constant intervals.
A simple one transaction is:
1. opening the /dev/ttyACM0
2. sending the following 10-bytes request to the device:
unsigned char req[] = {0x02, 0xfe, 0x01, 0x05, 0x08, 0x02, 0x01, 0x69, 0xab, 0x03};
3. reading response (frame of 74 bytes length).
4. closing the descriptor
I am doing this transaction with 5 seconds intervals.
Before the bad commit everything was working correctly: I've got a requests and
a responses in a timely manner.
After the bad commit more time I am using the kernel module, more problems I have.
The graph [2] is showing the problem.
As you can see after module load all seems fine but after about 30 minutes I've got
a plenty of EAGAINs when doing read()'s and trying to read back the data.
When I rmmod and insmod the cdc_acm module again, then the situation is starting
over again: running ok shortly after load, and more time it is running, more EAGAINs
I have when calling read().
As a bonus I can see the problem on the device itself:
The device is configured as you can see here on this screen [3].
It has two transmision LEDs: TX and RX. Blink duration is set for 100ms.
This is a recording before the bad commit when all is working fine: [4]
And this is with the bad commit: [5]
As you can see the TX led is blinking wrongly long (indicating transmission?)
and I have problems doing read() calls (EAGAIN).
Reported-by: Mariusz Bialonczyk <manio@xxxxxxxxxx>
Signed-off-by: Oliver Neukum <oneukum@xxxxxxxx>
Fixes: a81cf9799ad7 ("cdc-acm: implement put_char() and flush_chars()")
Cc: stable <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/usb/class/cdc-acm.c | 73 --------------------------------------------
drivers/usb/class/cdc-acm.h | 1
2 files changed, 74 deletions(-)
--- a/drivers/usb/class/cdc-acm.c
+++ b/drivers/usb/class/cdc-acm.c
@@ -705,20 +705,9 @@ static int acm_tty_write(struct tty_stru
}
if (acm->susp_count) {
- if (acm->putbuffer) {
- /* now to preserve order */
- usb_anchor_urb(acm->putbuffer->urb, &acm->delayed);
- acm->putbuffer = NULL;
- }
usb_anchor_urb(wb->urb, &acm->delayed);
spin_unlock_irqrestore(&acm->write_lock, flags);
return count;
- } else {
- if (acm->putbuffer) {
- /* at this point there is no good way to handle errors */
- acm_start_wb(acm, acm->putbuffer);
- acm->putbuffer = NULL;
- }
}
stat = acm_start_wb(acm, wb);
@@ -729,66 +718,6 @@ static int acm_tty_write(struct tty_stru
return count;
}
-static void acm_tty_flush_chars(struct tty_struct *tty)
-{
- struct acm *acm = tty->driver_data;
- struct acm_wb *cur;
- int err;
- unsigned long flags;
-
- spin_lock_irqsave(&acm->write_lock, flags);
-
- cur = acm->putbuffer;
- if (!cur) /* nothing to do */
- goto out;
-
- acm->putbuffer = NULL;
- err = usb_autopm_get_interface_async(acm->control);
- if (err < 0) {
- cur->use = 0;
- acm->putbuffer = cur;
- goto out;
- }
-
- if (acm->susp_count)
- usb_anchor_urb(cur->urb, &acm->delayed);
- else
- acm_start_wb(acm, cur);
-out:
- spin_unlock_irqrestore(&acm->write_lock, flags);
- return;
-}
-
-static int acm_tty_put_char(struct tty_struct *tty, unsigned char ch)
-{
- struct acm *acm = tty->driver_data;
- struct acm_wb *cur;
- int wbn;
- unsigned long flags;
-
-overflow:
- cur = acm->putbuffer;
- if (!cur) {
- spin_lock_irqsave(&acm->write_lock, flags);
- wbn = acm_wb_alloc(acm);
- if (wbn >= 0) {
- cur = &acm->wb[wbn];
- acm->putbuffer = cur;
- }
- spin_unlock_irqrestore(&acm->write_lock, flags);
- if (!cur)
- return 0;
- }
-
- if (cur->len == acm->writesize) {
- acm_tty_flush_chars(tty);
- goto overflow;
- }
-
- cur->buf[cur->len++] = ch;
- return 1;
-}
-
static int acm_tty_write_room(struct tty_struct *tty)
{
struct acm *acm = tty->driver_data;
@@ -1940,8 +1869,6 @@ static const struct tty_operations acm_o
.cleanup = acm_tty_cleanup,
.hangup = acm_tty_hangup,
.write = acm_tty_write,
- .put_char = acm_tty_put_char,
- .flush_chars = acm_tty_flush_chars,
.write_room = acm_tty_write_room,
.ioctl = acm_tty_ioctl,
.throttle = acm_tty_throttle,
--- a/drivers/usb/class/cdc-acm.h
+++ b/drivers/usb/class/cdc-acm.h
@@ -94,7 +94,6 @@ struct acm {
unsigned long read_urbs_free;
struct urb *read_urbs[ACM_NR];
struct acm_rb read_buffers[ACM_NR];
- struct acm_wb *putbuffer; /* for acm_tty_put_char() */
int rx_buflimit;
spinlock_t read_lock;
int write_used; /* number of non-empty write buffers */
