This is a note to let you know that I've just added the patch titled
Revert "cdc-acm: implement put_char() and flush_chars()"
to my usb git tree which can be found at git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git in the usb-linus branch.
The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)
The patch will hopefully also be merged in Linus's tree for the next -rc kernel release.
If you have any questions about this process, please let me know.
From df3aa13c7bbb307e172c37f193f9a7aa058d4739 Mon Sep 17 00:00:00 2001
From: Oliver Neukum oneukum@suse.com Date: Wed, 5 Sep 2018 17:56:46 +0200 Subject: Revert "cdc-acm: implement put_char() and flush_chars()"
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@skyboo.net Signed-off-by: Oliver Neukum oneukum@suse.com Fixes: a81cf9799ad7 ("cdc-acm: implement put_char() and flush_chars()") Cc: stable stable@vger.kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/usb/class/cdc-acm.c | 73 ------------------------------------- drivers/usb/class/cdc-acm.h | 1 - 2 files changed, 74 deletions(-)
diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c index 27346d69f393..f9b40a9dc4d3 100644 --- a/drivers/usb/class/cdc-acm.c +++ b/drivers/usb/class/cdc-acm.c @@ -780,20 +780,9 @@ static int acm_tty_write(struct tty_struct *tty, }
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); @@ -804,66 +793,6 @@ static int acm_tty_write(struct tty_struct *tty, 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; @@ -1987,8 +1916,6 @@ static const struct tty_operations acm_ops = { .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, diff --git a/drivers/usb/class/cdc-acm.h b/drivers/usb/class/cdc-acm.h index eacc116e83da..ca06b20d7af9 100644 --- a/drivers/usb/class/cdc-acm.h +++ b/drivers/usb/class/cdc-acm.h @@ -96,7 +96,6 @@ 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; u8 *notification_buffer; /* to reassemble fragmented notifications */