[PATCH v4] auxdisplay: Remove in_interrupt() usage.

From: Sebastian Andrzej Siewior
Date: Tue Feb 16 2021 - 13:28:00 EST


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
preemptible. 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 safe to sleep because it always is. in_interrupt() and related
context checks are being removed from non-core code.
Using schedule() to schedule (and 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@xxxxxxxxxxxxx
Cc: Miguel Ojeda Sandonis <miguel.ojeda.sandonis@xxxxxxxxx>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
---
v2…v4: - Spelling fixes got lot.
- Add a comment before cond_resched() as requested by Miguel Ojeda.
- Drop the ` ' comments.
v2…v3: Extend the commit message as suggested by Miguel Ojeda.
v1…v2: Spelling fixes.

drivers/auxdisplay/charlcd.c | 18 ++++++++----------
1 file changed, 8 insertions(+), 10 deletions(-)

diff --git a/drivers/auxdisplay/charlcd.c b/drivers/auxdisplay/charlcd.c
index f43430e9dceed..95accc941023a 100644
--- a/drivers/auxdisplay/charlcd.c
+++ b/drivers/auxdisplay/charlcd.c
@@ -470,12 +470,14 @@ 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))
+ if (((count + 1) & 0x1f) == 0) {
/*
- * let's be a little nice with other processes
- * that need some CPU
+ * charlcd_write() is invoked as a VFS->write() callback
+ * and as such it is > always invoked from preemptible
+ * context and may sleep.
*/
- schedule();
+ cond_resched();
+ }

if (get_user(c, tmp))
return -EFAULT;
@@ -537,12 +539,8 @@ 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