kernel/crash_core: suppress unknown crashkernel parameter warning

When booting with crashkernel= on the kernel command line a warning
similar to

    Kernel command line: ro console=ttyS0 crashkernel=256M
    Unknown kernel command line parameters "crashkernel=256M", will be passed to user space.

is printed.

This comes from crashkernel= being parsed independent from the kernel
parameter handling mechanism.  So the code in init/main.c doesn't know
that crashkernel= is a valid kernel parameter and prints this incorrect
warning.

Suppress the warning by adding a dummy early_param handler for
crashkernel=.

Link: https://lkml.kernel.org/r/20211208133443.6867-1-prudo@redhat.com
Fixes: 86d1919 ("init: print out unknown kernel parameters")
Signed-off-by: Philipp Rudo <prudo@redhat.com>
Acked-by: Baoquan He <bhe@redhat.com>
Cc: Andrew Halaney <ahalaney@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Author: prudo1

kernel/crash_core.c

@@ -6,6 +6,7 @@
 
 #include <linux/buildid.h>
 #include <linux/crash_core.h>
+#include <linux/init.h>
 #include <linux/utsname.h>
 #include <linux/vmalloc.h>
 
@@ -295,6 +296,16 @@ int __init parse_crashkernel_low(char *cmdline,
 				"crashkernel=", suffix_tbl[SUFFIX_LOW]);
 }
 
+/*
+ * Add a dummy early_param handler to mark crashkernel= as a known command line
+ * parameter and suppress incorrect warnings in init/main.c.
+ */
+static int __init parse_crashkernel_dummy(char *arg)
+{
+	return 0;
+}
+early_param("crashkernel", parse_crashkernel_dummy);
+
 Elf_Word *append_elf_note(Elf_Word *buf, char *name, unsigned int type,
 			  void *data, size_t data_len)
 {