On 2020-11-20, HAGIO KAZUHITO(萩尾 一仁) <k-hagio-ab@xxxxxxx> wrote:
> I've updated John's RFC crash patch to match 5.10-rc4 kernel.
> Changes from the RFC patch:
> - followed the following kernel commits
> cfe2790b163a ("printk: move printk_info into separate array")
> 74caba7f2a06 ("printk: move dictionary keys to dev_printk_info")
> f35efc78add6 ("printk: remove dict ring")
> - moved the added members in offset_table and size_table to the end
> of them
> - print offsets and sizes with "help -o" option
> - support "log -T" option
Thank you for this work. I've attached a followup "crash" patch to
correctly interpret the state value. With this followup patch applied,
this passes all my tests.
Note that support for "./crash --log ./vmcore" is still not
implemented. That can be done in a separate patch.
John Ogness
>From a825be51da728f668bfeb770f2a8cf1bc3ef6a23 Mon Sep 17 00:00:00 2001
From: John Ogness <john.ogness@xxxxxxxxxxxxx>
Date: Wed, 25 Nov 2020 05:27:53 +0106
Subject: [PATCH] printk: use committed/finalized state values
The ringbuffer entries use 2 state values (committed and finalized)
rather than a single flag to represent being available for reading.
Copy the definitions and state lookup function directly from the
kernel source and use the new states.
Signed-off-by: John Ogness <john.ogness@xxxxxxxxxxxxx>
Signed-off-by: Nikolay Borisov <nborisov@xxxxxxxx>
---
printk.c | 48 +++++++++++++++++++++++++++++++++++++++++-------
1 file changed, 41 insertions(+), 7 deletions(-)
diff --git a/printk.c b/printk.c
index 7be7218..ac135fc 100644
--- a/printk.c
+++ b/printk.c
@@ -1,12 +1,6 @@
#include "defs.h"
#include <ctype.h>
-#define DESC_SV_BITS (sizeof(unsigned long) * 8)
-#define DESC_COMMITTED_MASK (1UL << (DESC_SV_BITS - 1))
-#define DESC_REUSE_MASK (1UL << (DESC_SV_BITS - 2))
-#define DESC_FLAGS_MASK (DESC_COMMITTED_MASK | DESC_REUSE_MASK)
-#define DESC_ID_MASK (~DESC_FLAGS_MASK)
-
/* convenience struct for passing many values to helper functions */
struct prb_map {
char *prb;
@@ -21,6 +15,44 @@ struct prb_map {
char *text_data;
};
+/*
+ * desc_state and DESC_* definitions taken from kernel source:
+ *
+ * kernel/printk/printk_ringbuffer.h
+ */
+
+/* The possible responses of a descriptor state-query. */
+enum desc_state {
+ desc_miss = -1, /* ID mismatch (pseudo state) */
+ desc_reserved = 0x0, /* reserved, in use by writer */
+ desc_committed = 0x1, /* committed by writer, could get reopened */
+ desc_finalized = 0x2, /* committed, no further modification allowed */
+ desc_reusable = 0x3, /* free, not yet used by any writer */
+};
+
+#define DESC_SV_BITS (sizeof(unsigned long) * 8)
+#define DESC_FLAGS_SHIFT (DESC_SV_BITS - 2)
+#define DESC_FLAGS_MASK (3UL << DESC_FLAGS_SHIFT)
+#define DESC_STATE(sv) (3UL & (sv >> DESC_FLAGS_SHIFT))
+#define DESC_ID_MASK (~DESC_FLAGS_MASK)
+#define DESC_ID(sv) ((sv) & DESC_ID_MASK)
+
+/*
+ * get_desc_state() taken from kernel source:
+ *
+ * kernel/printk/printk_ringbuffer.c
+ */
+
+/* Query the state of a descriptor. */
+static enum desc_state get_desc_state(unsigned long id,
+ unsigned long state_val)
+{
+ if (id != DESC_ID(state_val))
+ return desc_miss;
+
+ return DESC_STATE(state_val);
+}
+
static void
init_offsets(void)
{
@@ -74,6 +106,7 @@ dump_record(struct prb_map *m, unsigned long id, int msg_flags)
unsigned short text_len;
unsigned long state_var;
unsigned int caller_id;
+ enum desc_state state;
unsigned char level;
unsigned long begin;
unsigned long next;
@@ -90,7 +123,8 @@ dump_record(struct prb_map *m, unsigned long id, int msg_flags)
/* skip non-committed record */
state_var = ULONG(desc + OFFSET(prb_desc_state_var) +
OFFSET(atomic_long_t_counter));
- if ((state_var & DESC_FLAGS_MASK) != DESC_COMMITTED_MASK)
+ state = get_desc_state(id, state_var);
+ if (state != desc_committed && state != desc_finalized)
return;
info = m->infos + ((id % m->desc_ring_count) * SIZE(printk_info));
--
2.20.1
--
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