Merge tag 'printk-for-5.13' of git://git.kernel.org/pub/scm/linux/kernel/git/printk/linux

Pull printk updates from Petr Mladek:

 - Stop synchronizing kernel log buffer readers by logbuf_lock. As a
   result, the access to the buffer is fully lockless now.

   Note that printk() itself still uses locks because it tries to flush
   the messages to the console immediately. Also the per-CPU temporary
   buffers are still there because they prevent infinite recursion and
   serialize backtraces from NMI. All this is going to change in the
   future.

 - kmsg_dump API rework and cleanup as a side effect of the logbuf_lock
   removal.

 - Make bstr_printf() aware that %pf and %pF formats could deference the
   given pointer.

 - Show also page flags by %pGp format.

 - Clarify the documentation for plain pointer printing.

 - Do not show no_hash_pointers warning multiple times.

 - Update Senozhatsky email address.

 - Some clean up.

* tag 'printk-for-5.13' of git://git.kernel.org/pub/scm/linux/kernel/git/printk/linux: (24 commits)
  lib/vsprintf.c: remove leftover 'f' and 'F' cases from bstr_printf()
  printk: clarify the documentation for plain pointer printing
  kernel/printk.c: Fixed mundane typos
  printk: rename vprintk_func to vprintk
  vsprintf: dump full information of page flags in pGp
  mm, slub: don't combine pr_err with INFO
  mm, slub: use pGp to print page flags
  MAINTAINERS: update Senozhatsky email address
  lib/vsprintf: do not show no_hash_pointers message multiple times
  printk: console: remove unnecessary safe buffer usage
  printk: kmsg_dump: remove _nolock() variants
  printk: remove logbuf_lock
  printk: introduce a kmsg_dump iterator
  printk: kmsg_dumper: remove @active field
  printk: add syslog_lock
  printk: use atomic64_t for devkmsg_user.seq
  printk: use seqcount_latch for clear_seq
  printk: introduce CONSOLE_LOG_MAX
  printk: consolidate kmsg_dump_get_buffer/syslog_print_all code
  printk: refactor kmsg_dump_get_buffer()
  ...

1 files changed, 12 insertions, 1 deletions

diff --git a/arch/um/kernel/kmsg_dump.c b/arch/um/kernel/kmsg_dump.c
index 6516ef1f8274..0224fcb36e22 100644
--- a/arch/um/kernel/kmsg_dump.c
+++ b/arch/um/kernel/kmsg_dump.c
@@ -1,5 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0
 #include <linux/kmsg_dump.h>
+#include <linux/spinlock.h>
 #include <linux/console.h>
 #include <linux/string.h>
 #include <shared/init.h>
@@ -9,8 +10,11 @@
 static void kmsg_dumper_stdout(struct kmsg_dumper *dumper,
 				enum kmsg_dump_reason reason)
 {
+	static struct kmsg_dump_iter iter;
+	static DEFINE_SPINLOCK(lock);
 	static char line[1024];
 	struct console *con;
+	unsigned long flags;
 	size_t len = 0;
 
 	/* only dump kmsg when no console is available */
@@ -29,11 +33,18 @@ static void kmsg_dumper_stdout(struct kmsg_dumper *dumper,
 	if (con)
 		return;
 
+	if (!spin_trylock_irqsave(&lock, flags))
+		return;
+
+	kmsg_dump_rewind(&iter);
+
 	printf("kmsg_dump:\n");
-	while (kmsg_dump_get_line(dumper, true, line, sizeof(line), &len)) {
+	while (kmsg_dump_get_line(&iter, true, line, sizeof(line), &len)) {
 		line[len] = '\0';
 		printf("%s", line);
 	}
+
+	spin_unlock_irqrestore(&lock, flags);
 }
 
 static struct kmsg_dumper kmsg_dumper = {