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From: Thomas Gleixner <tglx@linutronix.de>
To: LKML <linux-kernel@vger.kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
	"Ahmed S. Darwish" <a.darwish@linutronix.de>,
	Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
	Johan Hovold <johan@kernel.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	linux-usb@vger.kernel.org,
	Thomas Winischhofer <thomas@winischhofer.net>,
	Mathias Nyman <mathias.nyman@intel.com>,
	Valentina Manea <valentina.manea.m@gmail.com>,
	Shuah Khan <shuah@kernel.org>,
	Alan Stern <stern@rowland.harvard.edu>,
	linux-omap@vger.kernel.org, Kukjin Kim <kgene@kernel.org>,
	Krzysztof Kozlowski <krzk@kernel.org>,
	linux-arm-kernel@lists.infradead.org,
	linux-samsung-soc@vger.kernel.org,
	Felipe Balbi <balbi@kernel.org>,
	Duncan Sands <duncan.sands@free.fr>
Subject: [patch V2 02/13] USB: serial: keyspan_pda: Replace in_interrupt() usage
Date: Mon, 19 Oct 2020 12:06:31 +0200	[thread overview]
Message-ID: <20201019101109.753597069@linutronix.de> (raw)
In-Reply-To: <20201019100629.419020859@linutronix.de>

keyspan_pda_write() uses in_interrupt() to check whether it is safe to
invoke functions which might sleep.

The usage of in_interrupt() in drivers is phased out and Linus clearly
requested that code which changes behaviour depending on context should
either be seperated or the context be conveyed in an argument passed by the
caller, which usually knows the context.

Aside of that it does not cover all contexts which cannot sleep,
e.g. preempt disabled regions which cannot be reliably detected on all
kernel configurations.

With the current printk() implementation console->write() can be invoked
from almost any context. The upcoming rework of the console core will
provide thread context for console drivers which require to sleep.

For now, restrict the room query which can sleep to tty writes which happen
from preemptible task context.

The usability for dmesg output is limited anyway because it's almost
guaranteed to drop the 'LF' which is submitted after the dmesg line because
the device supports only one transfer on flight. Same for any printk()
which is coming in before the previous transfer has been done.

This new restriction does not make it worse than before, but it makes the
condition correct under all circumstances.

Signed-off-by: Ahmed S. Darwish <a.darwish@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Johan Hovold <johan@kernel.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: linux-usb@vger.kernel.org

---
 drivers/usb/serial/keyspan_pda.c |   10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

--- a/drivers/usb/serial/keyspan_pda.c
+++ b/drivers/usb/serial/keyspan_pda.c
@@ -477,10 +477,12 @@ static int keyspan_pda_write(struct tty_
 
 	count = (count > port->bulk_out_size) ? port->bulk_out_size : count;
 
-	/* Check if we might overrun the Tx buffer.   If so, ask the
-	   device how much room it really has.  This is done only on
-	   scheduler time, since usb_control_msg() sleeps. */
-	if (count > priv->tx_room && !in_interrupt()) {
+	/*
+	 * Check if we might overrun the Tx buffer. If so, ask the device
+	 * how much room it really has. This can only be invoked for tty
+	 * usage because the console write can't sleep.
+	 */
+	if (count > priv->tx_room && tty) {
 		u8 *room;
 
 		room = kmalloc(1, GFP_KERNEL);


  parent reply	other threads:[~2020-10-19 10:19 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-19 10:06 [patch V2 00/13] USB: Cleanup in_interupt/in_irq/in_atomic() usage Thomas Gleixner
2020-10-19 10:06 ` [patch V2 01/13] USB: sisusbvga: Make console support depend on BROKEN Thomas Gleixner
2020-10-19 10:06 ` Thomas Gleixner [this message]
2020-10-25 16:56   ` [patch V2 02/13] USB: serial: keyspan_pda: Replace in_interrupt() usage Johan Hovold
2020-10-26 12:47     ` Sebastian Andrzej Siewior
2020-10-27  8:16       ` Johan Hovold
2020-10-19 10:06 ` [patch V2 03/13] USB: serial: keyspan_pda: Consolidate room query Thomas Gleixner
2020-10-25 17:05   ` Johan Hovold
2020-10-19 10:06 ` [patch V2 04/13] USB: serial: digi_acceleport: Remove in_interrupt() usage Thomas Gleixner
2020-10-25 17:16   ` Johan Hovold
2020-10-26 14:03     ` [PATCH v3 04/13 ] " Sebastian Andrzej Siewior
2020-10-27  8:26       ` Johan Hovold
2020-10-19 10:06 ` [patch V2 05/13] usb: xhci: Remove in_interrupt() checks Thomas Gleixner
2020-10-19 10:06 ` [patch V2 06/13] usb: host: isp1362: Replace in_interrupt() usage Thomas Gleixner
2020-10-28 11:27   ` Greg Kroah-Hartman
2020-10-19 10:06 ` [patch V2 07/13] usbip: Remove in_interrupt() check Thomas Gleixner
2020-10-19 10:06 ` [patch V2 08/13] usb: hosts: Remove in_interrupt() from comments Thomas Gleixner
2020-10-19 16:28   ` Alan Stern
2020-10-19 10:06 ` [patch V2 09/13] USB: host: ehci-pmcmsp: Cleanup usb_hcd_msp_remove() Thomas Gleixner
2020-10-19 16:28   ` Alan Stern
2020-10-19 10:06 ` [patch V2 10/13] usb: gadget: pxa27x_udc: Replace in_interrupt() usage in comments Thomas Gleixner
2020-10-19 10:06 ` [patch V2 11/13] usb: gadget: udc: Remove in_interrupt()/in_irq() from comments Thomas Gleixner
2020-10-19 16:28   ` Alan Stern
2020-10-19 10:06 ` [patch V2 12/13] usb: core: Replace in_interrupt() in comments Thomas Gleixner
2020-10-19 16:28   ` Alan Stern
2020-10-19 10:06 ` [patch V2 13/13] usb: atm: Replace in_interrupt() usage in comment Thomas Gleixner
2020-10-19 10:28   ` Duncan Sands

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