[PATCH] panic: only warn about deprecated panic_print on write access

[Gal Pressman]

The panic_print_deprecated() warning is being triggered on both read and
write operations to the panic_print parameter.

This causes spurious warnings when users run 'sysctl -a' to list all
sysctl values, since that command reads /proc/sys/kernel/panic_print and
triggers the deprecation notice.

Modify the handlers to only emit the deprecation warning when the
parameter is actually being set:

 - sysctl_panic_print_handler(): check 'write' flag before warning.
 - panic_print_get(): remove the deprecation call entirely.

This way, users are only warned when they actively try to use the
deprecated parameter, not when passively querying system state.

Fixes: ee13240cd78b ("panic: add note that panic_print sysctl interface is deprecated")
Fixes: 2683df6539cb ("panic: add note that 'panic_print' parameter is deprecated")
Cc: Feng Tang <feng.tang@xxxxxxxxxxxxxxxxx>
Reviewed-by: Mark Bloch <mbloch@xxxxxxxxxx>
Reviewed-by: Nimrod Oren <noren@xxxxxxxxxx>
Signed-off-by: Gal Pressman <gal@xxxxxxxxxx>
---
 kernel/panic.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/panic.c b/kernel/panic.c
index 0d52210a9e2b..0c20fcaae98a 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -131,7 +131,8 @@ static int proc_taint(const struct ctl_table *table, int write,
 static int sysctl_panic_print_handler(const struct ctl_table *table, int write,
 			   void *buffer, size_t *lenp, loff_t *ppos)
 {
-	panic_print_deprecated();
+	if (write)
+		panic_print_deprecated();
 	return proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
 }
 
@@ -1014,7 +1015,6 @@ static int panic_print_set(const char *val, const struct kernel_param *kp)
 
 static int panic_print_get(char *val, const struct kernel_param *kp)
 {
-	panic_print_deprecated();
 	return  param_get_ulong(val, kp);
 }
 
-- 
2.40.1