printk: ringbuffer: change representation of states

Rather than deriving the state by evaluating bits within the flags
area of the state variable, assign the states explicit values and
set those values in the flags area. Introduce macros to make it
simple to read and write state values for the state variable.

Although the functionality is preserved, the binary representation
for the states is changed.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20200914123354.832-5-john.ogness@linutronix.de

2 files changed, 27 insertions, 32 deletions

diff --git a/kernel/printk/printk_ringbuffer.c b/kernel/printk/printk_ringbuffer.c
index 5a9c7c8cff7b..c0d31185ccbf 100644
--- a/kernel/printk/printk_ringbuffer.c
+++ b/kernel/printk/printk_ringbuffer.c
@@ -348,14 +348,6 @@ static bool data_check_size(struct prb_data_ring *data_ring, unsigned int size)
 	return true;
 }
 
-/* The possible responses of a descriptor state-query. */
-enum desc_state {
-	desc_miss,	/* ID mismatch */
-	desc_reserved,	/* reserved, in use by writer */
-	desc_committed, /* committed, writer is done */
-	desc_reusable,	/* free, not yet used by any writer */
-};
-
 /* Query the state of a descriptor. */
 static enum desc_state get_desc_state(unsigned long id,
 				      unsigned long state_val)
@@ -363,13 +355,7 @@ static enum desc_state get_desc_state(unsigned long id,
 	if (id != DESC_ID(state_val))
 		return desc_miss;
 
-	if (state_val & DESC_REUSE_MASK)
-		return desc_reusable;
-
-	if (state_val & DESC_COMMITTED_MASK)
-		return desc_committed;
-
-	return desc_reserved;
+	return DESC_STATE(state_val);
 }
 
 /*
@@ -484,8 +470,8 @@ out:
 static void desc_make_reusable(struct prb_desc_ring *desc_ring,
 			       unsigned long id)
 {
-	unsigned long val_committed = id | DESC_COMMITTED_MASK;
-	unsigned long val_reusable = val_committed | DESC_REUSE_MASK;
+	unsigned long val_committed = DESC_SV(id, desc_committed);
+	unsigned long val_reusable = DESC_SV(id, desc_reusable);
 	struct prb_desc *desc = to_desc(desc_ring, id);
 	atomic_long_t *state_var = &desc->state_var;
 
@@ -921,7 +907,7 @@ static bool desc_reserve(struct printk_ringbuffer *rb, unsigned long *id_out)
 	 */
 	prev_state_val = atomic_long_read(&desc->state_var); /* LMM(desc_reserve:E) */
 	if (prev_state_val &&
-	    prev_state_val != (id_prev_wrap | DESC_COMMITTED_MASK | DESC_REUSE_MASK)) {
+	    get_desc_state(id_prev_wrap, prev_state_val) != desc_reusable) {
 		WARN_ON_ONCE(1);
 		return false;
 	}
@@ -935,7 +921,7 @@ static bool desc_reserve(struct printk_ringbuffer *rb, unsigned long *id_out)
 	 * This pairs with desc_read:D.
 	 */
 	if (!atomic_long_try_cmpxchg(&desc->state_var, &prev_state_val,
-				     id | 0)) { /* LMM(desc_reserve:F) */
+			DESC_SV(id, desc_reserved))) { /* LMM(desc_reserve:F) */
 		WARN_ON_ONCE(1);
 		return false;
 	}
@@ -1254,7 +1240,7 @@ void prb_commit(struct prb_reserved_entry *e)
 {
 	struct prb_desc_ring *desc_ring = &e->rb->desc_ring;
 	struct prb_desc *d = to_desc(desc_ring, e->id);
-	unsigned long prev_state_val = e->id | 0;
+	unsigned long prev_state_val = DESC_SV(e->id, desc_reserved);
 
 	/* Now the writer has finished all writing: LMM(prb_commit:A) */
 
@@ -1267,7 +1253,7 @@ void prb_commit(struct prb_reserved_entry *e)
 	 * this. This pairs with desc_read:B.
 	 */
 	if (!atomic_long_try_cmpxchg(&d->state_var, &prev_state_val,
-				     e->id | DESC_COMMITTED_MASK)) { /* LMM(prb_commit:B) */
+			DESC_SV(e->id, desc_committed))) { /* LMM(prb_commit:B) */
 		WARN_ON_ONCE(1);
 	}
 
diff --git a/kernel/printk/printk_ringbuffer.h b/kernel/printk/printk_ringbuffer.h
index e6302da041f9..a9d85a6727b1 100644
--- a/kernel/printk/printk_ringbuffer.h
+++ b/kernel/printk/printk_ringbuffer.h
@@ -112,16 +112,25 @@ struct prb_reserved_entry {
 	unsigned int			text_space;
 };
 
-#define _DATA_SIZE(sz_bits)		(1UL << (sz_bits))
-#define _DESCS_COUNT(ct_bits)		(1U << (ct_bits))
-#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)
-#define DESC_ID(sv)			((sv) & DESC_ID_MASK)
-#define FAILED_LPOS			0x1
-#define NO_LPOS				0x3
+/* 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 */
+	desc_reusable	= 0x3,	/* free, not yet used by any writer */
+};
+
+#define _DATA_SIZE(sz_bits)	(1UL << (sz_bits))
+#define _DESCS_COUNT(ct_bits)	(1U << (ct_bits))
+#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_SV(id, state)	(((unsigned long)state << DESC_FLAGS_SHIFT) | id)
+#define DESC_ID_MASK		(~DESC_FLAGS_MASK)
+#define DESC_ID(sv)		((sv) & DESC_ID_MASK)
+#define FAILED_LPOS		0x1
+#define NO_LPOS			0x3
 
 #define FAILED_BLK_LPOS	\
 {				\
@@ -213,7 +222,7 @@ struct prb_reserved_entry {
  */
 #define BLK0_LPOS(sz_bits)	(-(_DATA_SIZE(sz_bits)))
 #define DESC0_ID(ct_bits)	DESC_ID(-(_DESCS_COUNT(ct_bits) + 1))
-#define DESC0_SV(ct_bits)	(DESC_COMMITTED_MASK | DESC_REUSE_MASK | DESC0_ID(ct_bits))
+#define DESC0_SV(ct_bits)	DESC_SV(DESC0_ID(ct_bits), desc_reusable)
 
 /*
  * Define a ringbuffer with an external text data buffer. The same as