Commit 10dcb06d authored by John Ogness's avatar John Ogness Committed by Petr Mladek
Browse files

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: default avatarJohn Ogness <john.ogness@linutronix.de>
Reviewed-by: default avatarPetr Mladek <pmladek@suse.com>
Signed-off-by: default avatarPetr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20200914123354.832-5-john.ogness@linutronix.de
parent cc5c7041

Documentation/admin-guide/kdump/gdbmacros.txt

+8 −4
Original line number Diff line number Diff line
@@ -295,9 +295,12 @@ document dump_record 
end



define dmesg

	set var $desc_committed = 1UL << ((sizeof(long) * 8) - 1)

	set var $flags_mask = 3UL << ((sizeof(long) * 8) - 2)

	set var $id_mask = ~$flags_mask

	# definitions from kernel/printk/printk_ringbuffer.h

	set var $desc_committed = 1

	set var $desc_sv_bits = sizeof(long) * 8

	set var $desc_flags_shift = $desc_sv_bits - 2

	set var $desc_flags_mask = 3 << $desc_flags_shift

	set var $id_mask = ~$desc_flags_mask



	set var $desc_count = 1U << prb->desc_ring.count_bits

	set var $prev_flags = 0
@@ -309,7 +312,8 @@ define dmesg 
		set var $desc = &prb->desc_ring.descs[$id % $desc_count]



		# skip non-committed record

		if (($desc->state_var.counter & $flags_mask) == $desc_committed)

		set var $state = 3 & ($desc->state_var.counter >> $desc_flags_shift)

		if ($state == $desc_committed)

			dump_record $desc $prev_flags

			set var $prev_flags = $desc->info.flags

		end

kernel/printk/printk_ringbuffer.c

+7 −21
Original line number Diff line number Diff line
@@ -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);

	}

kernel/printk/printk_ringbuffer.h

+20 −11
Original line number Diff line number Diff line
@@ -112,12 +112,21 @@ struct prb_reserved_entry { 
	unsigned int			text_space;

};



/* 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_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_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
@@ -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

scripts/gdb/linux/dmesg.py

+6 −5
Original line number Diff line number Diff line
@@ -78,10 +78,10 @@ class LxDmesg(gdb.Command): 
        len_off = off + printk_info_type.get_type()['text_len'].bitpos // 8



        # definitions from kernel/printk/printk_ringbuffer.h

        desc_committed = 1

        desc_sv_bits = utils.get_long_type().sizeof * 8

        desc_committed_mask = 1 << (desc_sv_bits - 1)

        desc_reuse_mask = 1 << (desc_sv_bits - 2)

        desc_flags_mask = desc_committed_mask | desc_reuse_mask

        desc_flags_shift = desc_sv_bits - 2

        desc_flags_mask = 3 << desc_flags_shift

        desc_id_mask = ~desc_flags_mask



        # read in tail and head descriptor ids
@@ -96,8 +96,9 @@ class LxDmesg(gdb.Command): 
            desc_off = desc_sz * ind



            # skip non-committed record

            state = utils.read_u64(descs, desc_off + sv_off + counter_off) & desc_flags_mask

            if state != desc_committed_mask:

            state = 3 & (utils.read_u64(descs, desc_off + sv_off +

                                        counter_off) >> desc_flags_shift)

            if state != desc_committed:

                if did == head_id:

                    break

                did = (did + 1) & desc_id_mask

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