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Commit 533827c9 authored by Anton Vorontsov's avatar Anton Vorontsov Committed by Linus Torvalds
Browse files

printk: Implement some unlocked kmsg_dump functions 



If used from KDB, the locked variants are prone to deadlocks (suppose we
got to the debugger w/ the logbuf lock held).

So, we have to implement a few routines that grab no logbuf lock.

Yet we don't need these functions in modules, so we don't export them.

Signed-off-by: default avatarAnton Vorontsov <anton.vorontsov@linaro.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 1b499d05

include/linux/kmsg_dump.h

+16 −0
Original line number Diff line number Diff line
@@ -55,12 +55,17 @@ struct kmsg_dumper { 
#ifdef CONFIG_PRINTK

void kmsg_dump(enum kmsg_dump_reason reason);



bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,

			       char *line, size_t size, size_t *len);



bool kmsg_dump_get_line(struct kmsg_dumper *dumper, bool syslog,

			char *line, size_t size, size_t *len);



bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,

			  char *buf, size_t size, size_t *len);



void kmsg_dump_rewind_nolock(struct kmsg_dumper *dumper);



void kmsg_dump_rewind(struct kmsg_dumper *dumper);



int kmsg_dump_register(struct kmsg_dumper *dumper);
@@ -71,6 +76,13 @@ static inline void kmsg_dump(enum kmsg_dump_reason reason) 
{

}



static inline bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper,

					     bool syslog, const char *line,

					     size_t size, size_t *len)

{

	return false;

}



static inline bool kmsg_dump_get_line(struct kmsg_dumper *dumper, bool syslog,

				const char *line, size_t size, size_t *len)

{
@@ -83,6 +95,10 @@ static inline bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog, 
	return false;

}



static inline void kmsg_dump_rewind_nolock(struct kmsg_dumper *dumper)

{

}



static inline void kmsg_dump_rewind(struct kmsg_dumper *dumper)

{

}

kernel/printk.c

+55 −13
Original line number Diff line number Diff line
@@ -2510,7 +2510,7 @@ void kmsg_dump(enum kmsg_dump_reason reason) 
}



/**

 * kmsg_dump_get_line - retrieve one kmsg log line

 * kmsg_dump_get_line_nolock - retrieve one kmsg log line (unlocked version)

 * @dumper: registered kmsg dumper

 * @syslog: include the "<4>" prefixes

 * @line: buffer to copy the line to
@@ -2525,11 +2525,12 @@ void kmsg_dump(enum kmsg_dump_reason reason) 
 *

 * A return value of FALSE indicates that there are no more records to

 * read.

 *

 * The function is similar to kmsg_dump_get_line(), but grabs no locks.

 */

bool kmsg_dump_get_line(struct kmsg_dumper *dumper, bool syslog,

bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,

			       char *line, size_t size, size_t *len)

{

	unsigned long flags;

	struct log *msg;

	size_t l = 0;

	bool ret = false;
@@ -2537,7 +2538,6 @@ bool kmsg_dump_get_line(struct kmsg_dumper *dumper, bool syslog, 
	if (!dumper->active)

		goto out;



	raw_spin_lock_irqsave(&logbuf_lock, flags);

	if (dumper->cur_seq < log_first_seq) {

		/* messages are gone, move to first available one */

		dumper->cur_seq = log_first_seq;
@@ -2545,10 +2545,8 @@ bool kmsg_dump_get_line(struct kmsg_dumper *dumper, bool syslog, 
	}



	/* last entry */

	if (dumper->cur_seq >= log_next_seq) {

		raw_spin_unlock_irqrestore(&logbuf_lock, flags);

	if (dumper->cur_seq >= log_next_seq)

		goto out;

	}



	msg = log_from_idx(dumper->cur_idx);

	l = msg_print_text(msg, 0, syslog, line, size);
@@ -2556,12 +2554,41 @@ bool kmsg_dump_get_line(struct kmsg_dumper *dumper, bool syslog, 
	dumper->cur_idx = log_next(dumper->cur_idx);

	dumper->cur_seq++;

	ret = true;

	raw_spin_unlock_irqrestore(&logbuf_lock, flags);

out:

	if (len)

		*len = l;

	return ret;

}



/**

 * kmsg_dump_get_line - retrieve one kmsg log line

 * @dumper: registered kmsg dumper

 * @syslog: include the "<4>" prefixes

 * @line: buffer to copy the line to

 * @size: maximum size of the buffer

 * @len: length of line placed into buffer

 *

 * Start at the beginning of the kmsg buffer, with the oldest kmsg

 * record, and copy one record into the provided buffer.

 *

 * Consecutive calls will return the next available record moving

 * towards the end of the buffer with the youngest messages.

 *

 * A return value of FALSE indicates that there are no more records to

 * read.

 */

bool kmsg_dump_get_line(struct kmsg_dumper *dumper, bool syslog,

			char *line, size_t size, size_t *len)

{

	unsigned long flags;

	bool ret;



	raw_spin_lock_irqsave(&logbuf_lock, flags);

	ret = kmsg_dump_get_line_nolock(dumper, syslog, line, size, len);

	raw_spin_unlock_irqrestore(&logbuf_lock, flags);



	return ret;

}

EXPORT_SYMBOL_GPL(kmsg_dump_get_line);



/**
@@ -2663,6 +2690,24 @@ out: 
}

EXPORT_SYMBOL_GPL(kmsg_dump_get_buffer);



/**

 * kmsg_dump_rewind_nolock - reset the interator (unlocked version)

 * @dumper: registered kmsg dumper

 *

 * Reset the dumper's iterator so that kmsg_dump_get_line() and

 * kmsg_dump_get_buffer() can be called again and used multiple

 * times within the same dumper.dump() callback.

 *

 * The function is similar to kmsg_dump_rewind(), but grabs no locks.

 */

void kmsg_dump_rewind_nolock(struct kmsg_dumper *dumper)

{

	dumper->cur_seq = clear_seq;

	dumper->cur_idx = clear_idx;

	dumper->next_seq = log_next_seq;

	dumper->next_idx = log_next_idx;

}



/**

 * kmsg_dump_rewind - reset the interator

 * @dumper: registered kmsg dumper
@@ -2676,10 +2721,7 @@ void kmsg_dump_rewind(struct kmsg_dumper *dumper) 
	unsigned long flags;



	raw_spin_lock_irqsave(&logbuf_lock, flags);

	dumper->cur_seq = clear_seq;

	dumper->cur_idx = clear_idx;

	dumper->next_seq = log_next_seq;

	dumper->next_idx = log_next_idx;

	kmsg_dump_rewind_nolock(dumper);

	raw_spin_unlock_irqrestore(&logbuf_lock, flags);

}

EXPORT_SYMBOL_GPL(kmsg_dump_rewind);