Messages in this thread | | | From | Fabio Estevam <> | Date | Mon, 12 Jun 2017 08:55:44 -0300 | Subject | Re: [RFC, PATCH] imx: serial: Take tty->files_lock opportunistically |
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Hi Greg,
On Mon, Jun 12, 2017 at 3:46 AM, Greg Kroah-Hartman <gregkh@linuxfoundation.org> wrote:
>> linux-next is good, but mainline is not. >> >> Actually we need 4dec2f119e86f9c9 ("imx-serial: RX DMA startup >> latency") to be applied to 4.12-rc as well. > > Why? Can't it wait until 4.13-rc1?
Because without 4dec2f119e86f9c9 the imx serial driver behaves badly in 4.12-rc.
Just tested 4.12-rc5 and there is scary verbose warning:
[ 11.714904] ===================================================== [ 11.721006] WARNING: HARDIRQ-safe -> HARDIRQ-unsafe lock order detected [ 11.727628] 4.12.0-rc5 #413 Not tainted [ 11.731470] ----------------------------------------------------- [ 11.737572] rawtest/219 [HC0[0]:SC0[0]:HE0:SE1] is trying to acquire: [ 11.744018] (&(&tty->files_lock)->rlock){+.+...}, at: [<c04d83a0>] imx_startup+0x2c4/0x510 [ 11.752403] [ 11.752403] and this task is already holding: [ 11.758241] (&port_lock_key){-.....}, at: [<c04d81e8>] imx_startup+0x10c/0x510 [ 11.765571] which would create a new lock dependency: [ 11.770626] (&port_lock_key){-.....} -> (&(&tty->files_lock)->rlock){+.+...} [ 11.777791] [ 11.777791] but this new dependency connects a HARDIRQ-irq-safe lock: [ 11.785712] (&port_lock_key){-.....} [ 11.785726] ....
Complete stack at: https://pastebin.com/a2gUTwZK
This problem is caused by commit 18a4208826dd0 ("imx-serial: Reduce RX DMA startup latency when opening for reading").
linux-next has a fix for it: 4dec2f119e86f9c9 ("imx-serial: RX DMA startup latency")
Applying 4dec2f119e86f9c9 ("imx-serial: RX DMA startup latency") into 4.12-rc5 makes the issue go away.
Thanks
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