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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@gmail.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.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
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