linux-kernel - [PATCH printk v2 7/9] printk: Skip non-finalized records in panic

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20231106210730.115192-8-john.ogness@linutronix.de>
Date:   Mon,  6 Nov 2023 22:13:28 +0106
From:   John Ogness <john.ogness@...utronix.de>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Sergey Senozhatsky <senozhatsky@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org
Subject: [PATCH printk v2 7/9] printk: Skip non-finalized records in panic

Normally a reader will stop once reaching a non-finalized
record. However, when a panic happens, writers from other CPUs
(or an interrupted context on the panic CPU) may have been
writing a record and were unable to finalize it. The panic CPU
will reserve/commit/finalize its panic records, but these will
be located after the non-finalized records. This results in
panic() not flushing the panic messages.

Extend _prb_read_valid() to skip over non-finalized records if
on the panic CPU.

Fixes: 896fbe20b4e2 ("printk: use the lockless ringbuffer")
Signed-off-by: John Ogness <john.ogness@...utronix.de>
---
 kernel/printk/printk_ringbuffer.c | 22 ++++++++++++++++++++--
 1 file changed, 20 insertions(+), 2 deletions(-)

diff --git a/kernel/printk/printk_ringbuffer.c b/kernel/printk/printk_ringbuffer.c
index dc83569d3a3a..584d2b213876 100644
--- a/kernel/printk/printk_ringbuffer.c
+++ b/kernel/printk/printk_ringbuffer.c
@@ -2116,6 +2116,10 @@ u64 prb_next_reserve_seq(struct printk_ringbuffer *rb)
  *
  * On failure @seq is updated to a record that is not yet available to the
  * reader, but it will be the next record available to the reader.
+ *
+ * Note: When the current CPU is in panic, this function will skip over any
+ *       non-existent/non-finalized records in order to allow the panic CPU
+ *       to print any and all records that have been finalized.
  */
 static bool _prb_read_valid(struct printk_ringbuffer *rb, u64 *seq,
 			    struct printk_record *r, unsigned int *line_count)
@@ -2138,8 +2142,22 @@ static bool _prb_read_valid(struct printk_ringbuffer *rb, u64 *seq,
 			(*seq)++;
 
 		} else {
-			/* Non-existent/non-finalized record. Must stop. */
-			return false;
+			/*
+			 * Non-existent/non-finalized record. Must stop.
+			 *
+			 * For panic situations it cannot be expected that
+			 * non-finalized records will become finalized. But
+			 * there may be other finalized records beyond that
+			 * need to be printed for a panic situation. If this
+			 * is the panic CPU, skip this
+			 * non-existent/non-finalized record unless it is
+			 * at or beyond the head, in which case it is not
+			 * possible to continue.
+			 */
+			if (this_cpu_in_panic() && ((*seq + 1) < prb_next_reserve_seq(rb)))
+				(*seq)++;
+			else
+				return false;
 		}
 	}
 
-- 
2.39.2