From 71e159c64000467e94e08aefc144f5e1cdaa4aa0 Mon Sep 17 00:00:00 2001 From: John Ogness Date: Wed, 25 Nov 2020 05:27:53 +0106 Subject: [PATCH 2/2] printk: use committed/finalized state values An addendum to the previous crash commit a5531b24750e. 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 Signed-off-by: Nikolay Borisov --- printk.c | 48 +++++++++++++++++++++++++++++++++++++++++------- 1 file changed, 41 insertions(+), 7 deletions(-) diff --git a/printk.c b/printk.c index f6d54ce9d0d8..8658016e65bf 100644 --- a/printk.c +++ b/printk.c @@ -1,12 +1,6 @@ #include "defs.h" #include -#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)); -- 2.17.1