printk: fix kmsg_dump_get_buffer length calulations

stable inclusion
from stable-5.10.11
commit ce4d02da78a30e6ba6ed61a745900ae49985ba1e
bugzilla: 47621

--------------------------------

[ Upstream commit 89ccf18f ]

kmsg_dump_get_buffer() uses @syslog to determine if the syslog
prefix should be written to the buffer. However, when calculating
the maximum number of records that can fit into the buffer, it
always counts the bytes from the syslog prefix.

Use @syslog when calculating the maximum number of records that can
fit into the buffer.

Fixes: e2ae715d ("kmsg - kmsg_dump() use iterator to receive log buffer content")
Signed-off-by: NJohn Ogness <john.ogness@linutronix.de>
Reviewed-by: NPetr Mladek <pmladek@suse.com>
Acked-by: NSergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: NPetr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20210113164413.1599-1-john.ogness@linutronix.deSigned-off-by: NSasha Levin <sashal@kernel.org>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>
Acked-by: NXie XiuQi <xiexiuqi@huawei.com>

kernel/printk/printk.c

@@ -3376,7 +3376,7 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
 	while (prb_read_valid_info(prb, seq, &info, &line_count)) {
 		if (r.info->seq >= dumper->next_seq)
 			break;
-		l += get_record_print_text_size(&info, line_count, true, time);
+		l += get_record_print_text_size(&info, line_count, syslog, time);
 		seq = r.info->seq + 1;
 	}
 
@@ -3386,7 +3386,7 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
 						&info, &line_count)) {
 		if (r.info->seq >= dumper->next_seq)
 			break;
-		l -= get_record_print_text_size(&info, line_count, true, time);
+		l -= get_record_print_text_size(&info, line_count, syslog, time);
 		seq = r.info->seq + 1;
 	}