linux-kernel - [PATCH v3] auxdisplay: Remove in

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Date:   Sat, 13 Feb 2021 17:50:40 +0100
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Willy Tarreau <w@....eu>
Subject: [PATCH v3] auxdisplay: Remove in_interrupt() usage.

charlcd_write() is invoked as a VFS->write() callback and as such it is
always invoked from preemptible context and may sleep.

charlcd_puts() is invoked from register/unregister callback which is
preemtible. The reboot notifier callback is also invoked from
preemptible context.

Therefore there is no need to use `in_interrupt()' to figure out if it
is save to sleep because it always is. `in_interrupt()` and related
context checks are being removed from non-core code.
Using `schedule()' to schedule (an be friendly to others) is
discouraged and `cond_resched()' should be used instead.

Remove `in_interrupt()' and use `cond_resched()' to schedule every 32
iteration if needed.

Link: https://lkml.kernel.org/r/20200914204209.256266093@linutronix.de
Cc: Miguel Ojeda Sandonis <miguel.ojeda.sandonis@...il.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
---
v2…v3: Extend the commit message as suggested by Miguel Ojeda.
v1…v2: Spelling fixes.

On 2021-02-10 22:46:23 [+0100], Miguel Ojeda wrote:
> Hi Sebastian,
Hi Miguel,

> Yeah, it is a bit confusing when reading without the context (it is
> hard to keep up with everything going on unless you work full-time on
> it :-)

Sorry for leaving it out. I though it is not needed since it was not
needed.

> > since this patch was small, simple and removing not required code I kept
> > it out. Is this enough information for you?
> 
> If you don't mind, please add a quick sentence like (I can do it on my
> side too):
> 
>     `in_interrupt()` and related context checks are being removed
>     from non-core code.
> 
> Plus the tag:
> 
>     Link: https://lore.kernel.org/r/20200914204209.256266093@linutronix.de/

Added as suggested.

 drivers/auxdisplay/charlcd.c | 16 ++++------------
 1 file changed, 4 insertions(+), 12 deletions(-)

diff --git a/drivers/auxdisplay/charlcd.c b/drivers/auxdisplay/charlcd.c
index f43430e9dceed..fbfce95919f72 100644
--- a/drivers/auxdisplay/charlcd.c
+++ b/drivers/auxdisplay/charlcd.c
@@ -470,12 +470,8 @@ static ssize_t charlcd_write(struct file *file, const char __user *buf,
 	char c;
 
 	for (; count-- > 0; (*ppos)++, tmp++) {
-		if (!in_interrupt() && (((count + 1) & 0x1f) == 0))
-			/*
-			 * let's be a little nice with other processes
-			 * that need some CPU
-			 */
-			schedule();
+		if (((count + 1) & 0x1f) == 0)
+			cond_resched();
 
 		if (get_user(c, tmp))
 			return -EFAULT;
@@ -537,12 +533,8 @@ static void charlcd_puts(struct charlcd *lcd, const char *s)
 	int count = strlen(s);
 
 	for (; count-- > 0; tmp++) {
-		if (!in_interrupt() && (((count + 1) & 0x1f) == 0))
-			/*
-			 * let's be a little nice with other processes
-			 * that need some CPU
-			 */
-			schedule();
+		if (((count + 1) & 0x1f) == 0)
+			cond_resched();
 
 		charlcd_write_char(lcd, *tmp);
 	}
-- 
2.30.0