[PATCH next v4 00/15] printk: remove logbuf_lock

[PATCH next v4 00/15] printk: remove logbuf_lock

[John Ogness]

Hello,

Here is v4 of a series to remove @logbuf_lock, exposing the
ringbuffer locklessly to both readers and writers. v3 is
here [0].

Since @logbuf_lock was protecting much more than just the
ringbuffer, this series clarifies and cleans up the various
protections using comments, lockless accessors, atomic types,
and a new finer-grained @syslog_lock.

Removing @logbuf_lock required changing the semantics of the
kmsg_dumper callback in order to work locklessly. This series
adjusts all kmsg_dumpers and users of the kmsg_dump_get_*()
functions for the new semantics.

This series is based on next-20210303.

Changes since v3:

- disable interrupts in the arch/um kmsg_dumper

- reduce CONSOLE_LOG_MAX value from 4096 back to 1024 to revert
  the increasd 3KiB static memory footprint

- change the kmsg_dumper() callback prototype back to how it
  was because some dumpers need the registered object for
  container_of() usage

- for kmsg_dump_get_line()/kmsg_dump_get_buffer() restrict the
  minimal allowed sequence number to the cleared sequence number

John Ogness

[0] https://lore.kernel.org/lkml/20210225202438.28985-1-john.ogness@linutronix.de/

John Ogness (15):
  um: synchronize kmsg_dumper
  mtd: mtdoops: synchronize kmsg_dumper
  printk: limit second loop of syslog_print_all
  printk: kmsg_dump: remove unused fields
  printk: refactor kmsg_dump_get_buffer()
  printk: consolidate kmsg_dump_get_buffer/syslog_print_all code
  printk: introduce CONSOLE_LOG_MAX
  printk: use seqcount_latch for clear_seq
  printk: use atomic64_t for devkmsg_user.seq
  printk: add syslog_lock
  printk: kmsg_dumper: remove @active field
  printk: introduce a kmsg_dump iterator
  printk: remove logbuf_lock
  printk: kmsg_dump: remove _nolock() variants
  printk: console: remove unnecessary safe buffer usage

 arch/powerpc/kernel/nvram_64.c |   8 +-
 arch/powerpc/xmon/xmon.c       |   6 +-
 arch/um/kernel/kmsg_dump.c     |  13 +-
 drivers/hv/vmbus_drv.c         |   4 +-
 drivers/mtd/mtdoops.c          |  17 +-
 fs/pstore/platform.c           |   5 +-
 include/linux/kmsg_dump.h      |  47 ++--
 kernel/debug/kdb/kdb_main.c    |  10 +-
 kernel/printk/internal.h       |   4 +-
 kernel/printk/printk.c         | 464 +++++++++++++++++----------------
 kernel/printk/printk_safe.c    |  27 +-
 11 files changed, 310 insertions(+), 295 deletions(-)

-- 
2.20.1

[PATCH next v4 11/15] printk: kmsg_dumper: remove @active field

[John Ogness]

All 6 kmsg_dumpers do not benefit from the @active flag:

  (provide their own synchronization)
  - arch/powerpc/kernel/nvram_64.c
  - arch/um/kernel/kmsg_dump.c
  - drivers/mtd/mtdoops.c
  - fs/pstore/platform.c

  (only dump on KMSG_DUMP_PANIC, which does not require
  synchronization)
  - arch/powerpc/platforms/powernv/opal-kmsg.c
  - drivers/hv/vmbus_drv.c

The other 2 kmsg_dump users also do not rely on @active:

  (hard-code @active to always be true)
  - arch/powerpc/xmon/xmon.c
  - kernel/debug/kdb/kdb_main.c

Therefore, @active can be removed.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
---
 arch/powerpc/xmon/xmon.c    |  2 +-
 include/linux/kmsg_dump.h   |  2 --
 kernel/debug/kdb/kdb_main.c |  2 +-
 kernel/printk/printk.c      | 10 +---------
 4 files changed, 3 insertions(+), 13 deletions(-)

diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
index 3fe37495f63d..80ed3e1becf9 100644
--- a/arch/powerpc/xmon/xmon.c
+++ b/arch/powerpc/xmon/xmon.c
@@ -3001,7 +3001,7 @@ print_address(unsigned long addr)
 static void
 dump_log_buf(void)
 {
-	struct kmsg_dumper dumper = { .active = 1 };
+	struct kmsg_dumper dumper;
 	unsigned char buf[128];
 	size_t len;
 
diff --git a/include/linux/kmsg_dump.h b/include/linux/kmsg_dump.h
index 070c994ff19f..84eaa2090efa 100644
--- a/include/linux/kmsg_dump.h
+++ b/include/linux/kmsg_dump.h
@@ -36,7 +36,6 @@ enum kmsg_dump_reason {
  * 		through the record iterator
  * @max_reason:	filter for highest reason number that should be dumped
  * @registered:	Flag that specifies if this is already registered
- * @active:	Flag that specifies if this is currently dumping
  * @cur_seq:	Points to the oldest message to dump
  * @next_seq:	Points after the newest message to dump
  */
@@ -44,7 +43,6 @@ struct kmsg_dumper {
 	struct list_head list;
 	void (*dump)(struct kmsg_dumper *dumper, enum kmsg_dump_reason reason);
 	enum kmsg_dump_reason max_reason;
-	bool active;
 	bool registered;
 
 	/* private state of the kmsg iterator */
diff --git a/kernel/debug/kdb/kdb_main.c b/kernel/debug/kdb/kdb_main.c
index 930ac1b25ec7..315169d5e119 100644
--- a/kernel/debug/kdb/kdb_main.c
+++ b/kernel/debug/kdb/kdb_main.c
@@ -2101,7 +2101,7 @@ static int kdb_dmesg(int argc, const char **argv)
 	int adjust = 0;
 	int n = 0;
 	int skip = 0;
-	struct kmsg_dumper dumper = { .active = 1 };
+	struct kmsg_dumper dumper;
 	size_t len;
 	char buf[201];
 
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index e794a08de00f..ce4cc64ba7c9 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -3408,8 +3408,6 @@ void kmsg_dump(enum kmsg_dump_reason reason)
 			continue;
 
 		/* initialize iterator with data about the stored records */
-		dumper->active = true;
-
 		logbuf_lock_irqsave(flags);
 		dumper->cur_seq = latched_seq_read_nolock(&clear_seq);
 		dumper->next_seq = prb_next_seq(prb);
@@ -3417,9 +3415,6 @@ void kmsg_dump(enum kmsg_dump_reason reason)
 
 		/* invoke dumper which will iterate over records */
 		dumper->dump(dumper, reason);
-
-		/* reset iterator */
-		dumper->active = false;
 	}
 	rcu_read_unlock();
 }
@@ -3454,9 +3449,6 @@ bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
 
 	prb_rec_init_rd(&r, &info, line, size);
 
-	if (!dumper->active)
-		goto out;
-
 	/* Read text or count text lines? */
 	if (line) {
 		if (!prb_read_valid(prb, dumper->cur_seq, &r))
@@ -3542,7 +3534,7 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
 	bool ret = false;
 	bool time = printk_time;
 
-	if (!dumper->active || !buf || !size)
+	if (!buf || !size)
 		goto out;
 
 	logbuf_lock_irqsave(flags);
-- 
2.20.1

[PATCH next v4 12/15] printk: introduce a kmsg_dump iterator

[John Ogness]

Rather than storing the iterator information in the registered
kmsg_dumper structure, create a separate iterator structure. The
kmsg_dump_iter structure can reside on the stack of the caller, thus
allowing lockless use of the kmsg_dump functions.

Update code that accesses the kernel logs using the kmsg_dumper
structure to use the new kmsg_dump_iter structure. For kmsg_dumpers,
this also means adding a call to kmsg_dump_rewind() to initialize
the iterator.

All this is in preparation for removal of @logbuf_lock.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Kees Cook <keescook@chromium.org> # pstore
---
 arch/powerpc/kernel/nvram_64.c |  8 +++--
 arch/powerpc/xmon/xmon.c       |  6 ++--
 arch/um/kernel/kmsg_dump.c     |  5 ++-
 drivers/hv/vmbus_drv.c         |  4 ++-
 drivers/mtd/mtdoops.c          |  5 ++-
 fs/pstore/platform.c           |  5 ++-
 include/linux/kmsg_dump.h      | 36 ++++++++++---------
 kernel/debug/kdb/kdb_main.c    | 10 +++---
 kernel/printk/printk.c         | 63 +++++++++++++++++-----------------
 9 files changed, 80 insertions(+), 62 deletions(-)

diff --git a/arch/powerpc/kernel/nvram_64.c b/arch/powerpc/kernel/nvram_64.c
index 532f22637783..3c8d9bbb51cf 100644
--- a/arch/powerpc/kernel/nvram_64.c
+++ b/arch/powerpc/kernel/nvram_64.c
@@ -647,6 +647,7 @@ static void oops_to_nvram(struct kmsg_dumper *dumper,
 {
 	struct oops_log_info *oops_hdr = (struct oops_log_info *)oops_buf;
 	static unsigned int oops_count = 0;
+	static struct kmsg_dump_iter iter;
 	static bool panicking = false;
 	static DEFINE_SPINLOCK(lock);
 	unsigned long flags;
@@ -681,13 +682,14 @@ static void oops_to_nvram(struct kmsg_dumper *dumper,
 		return;
 
 	if (big_oops_buf) {
-		kmsg_dump_get_buffer(dumper, false,
+		kmsg_dump_rewind(&iter);
+		kmsg_dump_get_buffer(&iter, false,
 				     big_oops_buf, big_oops_buf_sz, &text_len);
 		rc = zip_oops(text_len);
 	}
 	if (rc != 0) {
-		kmsg_dump_rewind(dumper);
-		kmsg_dump_get_buffer(dumper, false,
+		kmsg_dump_rewind(&iter);
+		kmsg_dump_get_buffer(&iter, false,
 				     oops_data, oops_data_sz, &text_len);
 		err_type = ERR_TYPE_KERNEL_PANIC;
 		oops_hdr->version = cpu_to_be16(OOPS_HDR_VERSION);
diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
index 80ed3e1becf9..5978b90a885f 100644
--- a/arch/powerpc/xmon/xmon.c
+++ b/arch/powerpc/xmon/xmon.c
@@ -3001,7 +3001,7 @@ print_address(unsigned long addr)
 static void
 dump_log_buf(void)
 {
-	struct kmsg_dumper dumper;
+	struct kmsg_dump_iter iter;
 	unsigned char buf[128];
 	size_t len;
 
@@ -3013,9 +3013,9 @@ dump_log_buf(void)
 	catch_memory_errors = 1;
 	sync();
 
-	kmsg_dump_rewind_nolock(&dumper);
+	kmsg_dump_rewind_nolock(&iter);
 	xmon_start_pagination();
-	while (kmsg_dump_get_line_nolock(&dumper, false, buf, sizeof(buf), &len)) {
+	while (kmsg_dump_get_line_nolock(&iter, false, buf, sizeof(buf), &len)) {
 		buf[len] = '\0';
 		printf("%s", buf);
 	}
diff --git a/arch/um/kernel/kmsg_dump.c b/arch/um/kernel/kmsg_dump.c
index a765d235e50e..0224fcb36e22 100644
--- a/arch/um/kernel/kmsg_dump.c
+++ b/arch/um/kernel/kmsg_dump.c
@@ -10,6 +10,7 @@
 static void kmsg_dumper_stdout(struct kmsg_dumper *dumper,
 				enum kmsg_dump_reason reason)
 {
+	static struct kmsg_dump_iter iter;
 	static DEFINE_SPINLOCK(lock);
 	static char line[1024];
 	struct console *con;
@@ -35,8 +36,10 @@ static void kmsg_dumper_stdout(struct kmsg_dumper *dumper,
 	if (!spin_trylock_irqsave(&lock, flags))
 		return;
 
+	kmsg_dump_rewind(&iter);
+
 	printf("kmsg_dump:\n");
-	while (kmsg_dump_get_line(dumper, true, line, sizeof(line), &len)) {
+	while (kmsg_dump_get_line(&iter, true, line, sizeof(line), &len)) {
 		line[len] = '\0';
 		printf("%s", line);
 	}
diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index 10dce9f91216..b341b144bde8 100644
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -1391,6 +1391,7 @@ static void vmbus_isr(void)
 static void hv_kmsg_dump(struct kmsg_dumper *dumper,
 			 enum kmsg_dump_reason reason)
 {
+	struct kmsg_dump_iter iter;
 	size_t bytes_written;
 	phys_addr_t panic_pa;
 
@@ -1404,7 +1405,8 @@ static void hv_kmsg_dump(struct kmsg_dumper *dumper,
 	 * Write dump contents to the page. No need to synchronize; panic should
 	 * be single-threaded.
 	 */
-	kmsg_dump_get_buffer(dumper, false, hv_panic_page, HV_HYP_PAGE_SIZE,
+	kmsg_dump_rewind(&iter);
+	kmsg_dump_get_buffer(&iter, false, hv_panic_page, HV_HYP_PAGE_SIZE,
 			     &bytes_written);
 	if (bytes_written)
 		hyperv_report_panic_msg(panic_pa, bytes_written);
diff --git a/drivers/mtd/mtdoops.c b/drivers/mtd/mtdoops.c
index 8bbfba40a554..862c4a889234 100644
--- a/drivers/mtd/mtdoops.c
+++ b/drivers/mtd/mtdoops.c
@@ -277,14 +277,17 @@ static void mtdoops_do_dump(struct kmsg_dumper *dumper,
 {
 	struct mtdoops_context *cxt = container_of(dumper,
 			struct mtdoops_context, dump);
+	struct kmsg_dump_iter iter;
 
 	/* Only dump oopses if dump_oops is set */
 	if (reason == KMSG_DUMP_OOPS && !dump_oops)
 		return;
 
+	kmsg_dump_rewind(&iter);
+
 	if (test_and_set_bit(0, &cxt->oops_buf_busy))
 		return;
-	kmsg_dump_get_buffer(dumper, true, cxt->oops_buf + MTDOOPS_HEADER_SIZE,
+	kmsg_dump_get_buffer(&iter, true, cxt->oops_buf + MTDOOPS_HEADER_SIZE,
 			     record_size - MTDOOPS_HEADER_SIZE, NULL);
 	clear_bit(0, &cxt->oops_buf_busy);
 
diff --git a/fs/pstore/platform.c b/fs/pstore/platform.c
index d963ae7902f9..b9614db48b1d 100644
--- a/fs/pstore/platform.c
+++ b/fs/pstore/platform.c
@@ -385,6 +385,7 @@ void pstore_record_init(struct pstore_record *record,
 static void pstore_dump(struct kmsg_dumper *dumper,
 			enum kmsg_dump_reason reason)
 {
+	struct kmsg_dump_iter iter;
 	unsigned long	total = 0;
 	const char	*why;
 	unsigned int	part = 1;
@@ -405,6 +406,8 @@ static void pstore_dump(struct kmsg_dumper *dumper,
 		}
 	}
 
+	kmsg_dump_rewind(&iter);
+
 	oopscount++;
 	while (total < kmsg_bytes) {
 		char *dst;
@@ -435,7 +438,7 @@ static void pstore_dump(struct kmsg_dumper *dumper,
 		dst_size -= header_size;
 
 		/* Write dump contents. */
-		if (!kmsg_dump_get_buffer(dumper, true, dst + header_size,
+		if (!kmsg_dump_get_buffer(&iter, true, dst + header_size,
 					  dst_size, &dump_size))
 			break;
 
diff --git a/include/linux/kmsg_dump.h b/include/linux/kmsg_dump.h
index 84eaa2090efa..36c8c57e1051 100644
--- a/include/linux/kmsg_dump.h
+++ b/include/linux/kmsg_dump.h
@@ -29,6 +29,16 @@ enum kmsg_dump_reason {
 	KMSG_DUMP_MAX
 };
 
+/**
+ * struct kmsg_dump_iter - iterator for retrieving kernel messages
+ * @cur_seq:	Points to the oldest message to dump
+ * @next_seq:	Points after the newest message to dump
+ */
+struct kmsg_dump_iter {
+	u64	cur_seq;
+	u64	next_seq;
+};
+
 /**
  * struct kmsg_dumper - kernel crash message dumper structure
  * @list:	Entry in the dumper list (private)
@@ -36,35 +46,29 @@ enum kmsg_dump_reason {
  * 		through the record iterator
  * @max_reason:	filter for highest reason number that should be dumped
  * @registered:	Flag that specifies if this is already registered
- * @cur_seq:	Points to the oldest message to dump
- * @next_seq:	Points after the newest message to dump
  */
 struct kmsg_dumper {
 	struct list_head list;
 	void (*dump)(struct kmsg_dumper *dumper, enum kmsg_dump_reason reason);
 	enum kmsg_dump_reason max_reason;
 	bool registered;
-
-	/* private state of the kmsg iterator */
-	u64 cur_seq;
-	u64 next_seq;
 };
 
 #ifdef CONFIG_PRINTK
 void kmsg_dump(enum kmsg_dump_reason reason);
 
-bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
+bool kmsg_dump_get_line_nolock(struct kmsg_dump_iter *iter, bool syslog,
 			       char *line, size_t size, size_t *len);
 
-bool kmsg_dump_get_line(struct kmsg_dumper *dumper, bool syslog,
+bool kmsg_dump_get_line(struct kmsg_dump_iter *iter, bool syslog,
 			char *line, size_t size, size_t *len);
 
-bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
+bool kmsg_dump_get_buffer(struct kmsg_dump_iter *iter, bool syslog,
 			  char *buf, size_t size, size_t *len_out);
 
-void kmsg_dump_rewind_nolock(struct kmsg_dumper *dumper);
+void kmsg_dump_rewind_nolock(struct kmsg_dump_iter *iter);
 
-void kmsg_dump_rewind(struct kmsg_dumper *dumper);
+void kmsg_dump_rewind(struct kmsg_dump_iter *iter);
 
 int kmsg_dump_register(struct kmsg_dumper *dumper);
 
@@ -76,30 +80,30 @@ static inline void kmsg_dump(enum kmsg_dump_reason reason)
 {
 }
 
-static inline bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper,
+static inline bool kmsg_dump_get_line_nolock(struct kmsg_dump_iter *iter,
 					     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,
+static inline bool kmsg_dump_get_line(struct kmsg_dump_iter *iter, bool syslog,
 				const char *line, size_t size, size_t *len)
 {
 	return false;
 }
 
-static inline bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
+static inline bool kmsg_dump_get_buffer(struct kmsg_dump_iter *iter, bool syslog,
 					char *buf, size_t size, size_t *len)
 {
 	return false;
 }
 
-static inline void kmsg_dump_rewind_nolock(struct kmsg_dumper *dumper)
+static inline void kmsg_dump_rewind_nolock(struct kmsg_dump_iter *iter)
 {
 }
 
-static inline void kmsg_dump_rewind(struct kmsg_dumper *dumper)
+static inline void kmsg_dump_rewind(struct kmsg_dump_iter *iter)
 {
 }
 
diff --git a/kernel/debug/kdb/kdb_main.c b/kernel/debug/kdb/kdb_main.c
index 315169d5e119..8544d7a55a57 100644
--- a/kernel/debug/kdb/kdb_main.c
+++ b/kernel/debug/kdb/kdb_main.c
@@ -2101,7 +2101,7 @@ static int kdb_dmesg(int argc, const char **argv)
 	int adjust = 0;
 	int n = 0;
 	int skip = 0;
-	struct kmsg_dumper dumper;
+	struct kmsg_dump_iter iter;
 	size_t len;
 	char buf[201];
 
@@ -2126,8 +2126,8 @@ static int kdb_dmesg(int argc, const char **argv)
 		kdb_set(2, setargs);
 	}
 
-	kmsg_dump_rewind_nolock(&dumper);
-	while (kmsg_dump_get_line_nolock(&dumper, 1, NULL, 0, NULL))
+	kmsg_dump_rewind_nolock(&iter);
+	while (kmsg_dump_get_line_nolock(&iter, 1, NULL, 0, NULL))
 		n++;
 
 	if (lines < 0) {
@@ -2159,8 +2159,8 @@ static int kdb_dmesg(int argc, const char **argv)
 	if (skip >= n || skip < 0)
 		return 0;
 
-	kmsg_dump_rewind_nolock(&dumper);
-	while (kmsg_dump_get_line_nolock(&dumper, 1, buf, sizeof(buf), &len)) {
+	kmsg_dump_rewind_nolock(&iter);
+	while (kmsg_dump_get_line_nolock(&iter, 1, buf, sizeof(buf), &len)) {
 		if (skip) {
 			skip--;
 			continue;
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index ce4cc64ba7c9..b49dee256947 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -3390,7 +3390,6 @@ EXPORT_SYMBOL_GPL(kmsg_dump_reason_str);
 void kmsg_dump(enum kmsg_dump_reason reason)
 {
 	struct kmsg_dumper *dumper;
-	unsigned long flags;
 
 	rcu_read_lock();
 	list_for_each_entry_rcu(dumper, &dump_list, list) {
@@ -3407,12 +3406,6 @@ void kmsg_dump(enum kmsg_dump_reason reason)
 		if (reason > max_reason)
 			continue;
 
-		/* initialize iterator with data about the stored records */
-		logbuf_lock_irqsave(flags);
-		dumper->cur_seq = latched_seq_read_nolock(&clear_seq);
-		dumper->next_seq = prb_next_seq(prb);
-		logbuf_unlock_irqrestore(flags);
-
 		/* invoke dumper which will iterate over records */
 		dumper->dump(dumper, reason);
 	}
@@ -3421,7 +3414,7 @@ void kmsg_dump(enum kmsg_dump_reason reason)
 
 /**
  * kmsg_dump_get_line_nolock - retrieve one kmsg log line (unlocked version)
- * @dumper: registered kmsg dumper
+ * @iter: kmsg dump iterator
  * @syslog: include the "<4>" prefixes
  * @line: buffer to copy the line to
  * @size: maximum size of the buffer
@@ -3438,24 +3431,28 @@ void kmsg_dump(enum kmsg_dump_reason reason)
  *
  * The function is similar to kmsg_dump_get_line(), but grabs no locks.
  */
-bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
+bool kmsg_dump_get_line_nolock(struct kmsg_dump_iter *iter, bool syslog,
 			       char *line, size_t size, size_t *len)
 {
+	u64 min_seq = latched_seq_read_nolock(&clear_seq);
 	struct printk_info info;
 	unsigned int line_count;
 	struct printk_record r;
 	size_t l = 0;
 	bool ret = false;
 
+	if (iter->cur_seq < min_seq)
+		iter->cur_seq = min_seq;
+
 	prb_rec_init_rd(&r, &info, line, size);
 
 	/* Read text or count text lines? */
 	if (line) {
-		if (!prb_read_valid(prb, dumper->cur_seq, &r))
+		if (!prb_read_valid(prb, iter->cur_seq, &r))
 			goto out;
 		l = record_print_text(&r, syslog, printk_time);
 	} else {
-		if (!prb_read_valid_info(prb, dumper->cur_seq,
+		if (!prb_read_valid_info(prb, iter->cur_seq,
 					 &info, &line_count)) {
 			goto out;
 		}
@@ -3464,7 +3461,7 @@ bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
 
 	}
 
-	dumper->cur_seq = r.info->seq + 1;
+	iter->cur_seq = r.info->seq + 1;
 	ret = true;
 out:
 	if (len)
@@ -3474,7 +3471,7 @@ bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
 
 /**
  * kmsg_dump_get_line - retrieve one kmsg log line
- * @dumper: registered kmsg dumper
+ * @iter: kmsg dump iterator
  * @syslog: include the "<4>" prefixes
  * @line: buffer to copy the line to
  * @size: maximum size of the buffer
@@ -3489,14 +3486,14 @@ bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
  * 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,
+bool kmsg_dump_get_line(struct kmsg_dump_iter *iter, bool syslog,
 			char *line, size_t size, size_t *len)
 {
 	unsigned long flags;
 	bool ret;
 
 	logbuf_lock_irqsave(flags);
-	ret = kmsg_dump_get_line_nolock(dumper, syslog, line, size, len);
+	ret = kmsg_dump_get_line_nolock(iter, syslog, line, size, len);
 	logbuf_unlock_irqrestore(flags);
 
 	return ret;
@@ -3505,7 +3502,7 @@ EXPORT_SYMBOL_GPL(kmsg_dump_get_line);
 
 /**
  * kmsg_dump_get_buffer - copy kmsg log lines
- * @dumper: registered kmsg dumper
+ * @iter: kmsg dump iterator
  * @syslog: include the "<4>" prefixes
  * @buf: buffer to copy the line to
  * @size: maximum size of the buffer
@@ -3522,9 +3519,10 @@ EXPORT_SYMBOL_GPL(kmsg_dump_get_line);
  * A return value of FALSE indicates that there are no more records to
  * read.
  */
-bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
+bool kmsg_dump_get_buffer(struct kmsg_dump_iter *iter, bool syslog,
 			  char *buf, size_t size, size_t *len_out)
 {
+	u64 min_seq = latched_seq_read_nolock(&clear_seq);
 	struct printk_info info;
 	struct printk_record r;
 	unsigned long flags;
@@ -3537,16 +3535,19 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
 	if (!buf || !size)
 		goto out;
 
+	if (iter->cur_seq < min_seq)
+		iter->cur_seq = min_seq;
+
 	logbuf_lock_irqsave(flags);
-	if (prb_read_valid_info(prb, dumper->cur_seq, &info, NULL)) {
-		if (info.seq != dumper->cur_seq) {
+	if (prb_read_valid_info(prb, iter->cur_seq, &info, NULL)) {
+		if (info.seq != iter->cur_seq) {
 			/* messages are gone, move to first available one */
-			dumper->cur_seq = info.seq;
+			iter->cur_seq = info.seq;
 		}
 	}
 
 	/* last entry */
-	if (dumper->cur_seq >= dumper->next_seq) {
+	if (iter->cur_seq >= iter->next_seq) {
 		logbuf_unlock_irqrestore(flags);
 		goto out;
 	}
@@ -3557,7 +3558,7 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
 	 * because this function (by way of record_print_text()) will
 	 * not write more than size-1 bytes of text into @buf.
 	 */
-	seq = find_first_fitting_seq(dumper->cur_seq, dumper->next_seq,
+	seq = find_first_fitting_seq(iter->cur_seq, iter->next_seq,
 				     size - 1, syslog, time);
 
 	/*
@@ -3570,7 +3571,7 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
 
 	len = 0;
 	prb_for_each_record(seq, prb, seq, &r) {
-		if (r.info->seq >= dumper->next_seq)
+		if (r.info->seq >= iter->next_seq)
 			break;
 
 		len += record_print_text(&r, syslog, time);
@@ -3579,7 +3580,7 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
 		prb_rec_init_rd(&r, &info, buf + len, size - len);
 	}
 
-	dumper->next_seq = next_seq;
+	iter->next_seq = next_seq;
 	ret = true;
 	logbuf_unlock_irqrestore(flags);
 out:
@@ -3591,7 +3592,7 @@ EXPORT_SYMBOL_GPL(kmsg_dump_get_buffer);
 
 /**
  * kmsg_dump_rewind_nolock - reset the iterator (unlocked version)
- * @dumper: registered kmsg dumper
+ * @iter: kmsg dump iterator
  *
  * Reset the dumper's iterator so that kmsg_dump_get_line() and
  * kmsg_dump_get_buffer() can be called again and used multiple
@@ -3599,26 +3600,26 @@ EXPORT_SYMBOL_GPL(kmsg_dump_get_buffer);
  *
  * The function is similar to kmsg_dump_rewind(), but grabs no locks.
  */
-void kmsg_dump_rewind_nolock(struct kmsg_dumper *dumper)
+void kmsg_dump_rewind_nolock(struct kmsg_dump_iter *iter)
 {
-	dumper->cur_seq = latched_seq_read_nolock(&clear_seq);
-	dumper->next_seq = prb_next_seq(prb);
+	iter->cur_seq = latched_seq_read_nolock(&clear_seq);
+	iter->next_seq = prb_next_seq(prb);
 }
 
 /**
  * kmsg_dump_rewind - reset the iterator
- * @dumper: registered kmsg dumper
+ * @iter: kmsg dump iterator
  *
  * 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.
  */
-void kmsg_dump_rewind(struct kmsg_dumper *dumper)
+void kmsg_dump_rewind(struct kmsg_dump_iter *iter)
 {
 	unsigned long flags;
 
 	logbuf_lock_irqsave(flags);
-	kmsg_dump_rewind_nolock(dumper);
+	kmsg_dump_rewind_nolock(iter);
 	logbuf_unlock_irqrestore(flags);
 }
 EXPORT_SYMBOL_GPL(kmsg_dump_rewind);
-- 
2.20.1

[PATCH next v4 14/15] printk: kmsg_dump: remove _nolock() variants

[John Ogness]

kmsg_dump_rewind() and kmsg_dump_get_line() are lockless, so there is
no need for _nolock() variants. Remove these functions and switch all
callers of the _nolock() variants.

The functions without _nolock() were chosen because they are already
exported to kernel modules.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
---
 arch/powerpc/xmon/xmon.c    |  4 +--
 include/linux/kmsg_dump.h   | 16 ----------
 kernel/debug/kdb/kdb_main.c |  8 ++---
 kernel/printk/printk.c      | 60 +++++--------------------------------
 4 files changed, 14 insertions(+), 74 deletions(-)

diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
index 5978b90a885f..bf7d69625a2e 100644
--- a/arch/powerpc/xmon/xmon.c
+++ b/arch/powerpc/xmon/xmon.c
@@ -3013,9 +3013,9 @@ dump_log_buf(void)
 	catch_memory_errors = 1;
 	sync();
 
-	kmsg_dump_rewind_nolock(&iter);
+	kmsg_dump_rewind(&iter);
 	xmon_start_pagination();
-	while (kmsg_dump_get_line_nolock(&iter, false, buf, sizeof(buf), &len)) {
+	while (kmsg_dump_get_line(&iter, false, buf, sizeof(buf), &len)) {
 		buf[len] = '\0';
 		printf("%s", buf);
 	}
diff --git a/include/linux/kmsg_dump.h b/include/linux/kmsg_dump.h
index 36c8c57e1051..906521c2329c 100644
--- a/include/linux/kmsg_dump.h
+++ b/include/linux/kmsg_dump.h
@@ -57,17 +57,12 @@ struct kmsg_dumper {
 #ifdef CONFIG_PRINTK
 void kmsg_dump(enum kmsg_dump_reason reason);
 
-bool kmsg_dump_get_line_nolock(struct kmsg_dump_iter *iter, bool syslog,
-			       char *line, size_t size, size_t *len);
-
 bool kmsg_dump_get_line(struct kmsg_dump_iter *iter, bool syslog,
 			char *line, size_t size, size_t *len);
 
 bool kmsg_dump_get_buffer(struct kmsg_dump_iter *iter, bool syslog,
 			  char *buf, size_t size, size_t *len_out);
 
-void kmsg_dump_rewind_nolock(struct kmsg_dump_iter *iter);
-
 void kmsg_dump_rewind(struct kmsg_dump_iter *iter);
 
 int kmsg_dump_register(struct kmsg_dumper *dumper);
@@ -80,13 +75,6 @@ static inline void kmsg_dump(enum kmsg_dump_reason reason)
 {
 }
 
-static inline bool kmsg_dump_get_line_nolock(struct kmsg_dump_iter *iter,
-					     bool syslog, const char *line,
-					     size_t size, size_t *len)
-{
-	return false;
-}
-
 static inline bool kmsg_dump_get_line(struct kmsg_dump_iter *iter, bool syslog,
 				const char *line, size_t size, size_t *len)
 {
@@ -99,10 +87,6 @@ static inline bool kmsg_dump_get_buffer(struct kmsg_dump_iter *iter, bool syslog
 	return false;
 }
 
-static inline void kmsg_dump_rewind_nolock(struct kmsg_dump_iter *iter)
-{
-}
-
 static inline void kmsg_dump_rewind(struct kmsg_dump_iter *iter)
 {
 }
diff --git a/kernel/debug/kdb/kdb_main.c b/kernel/debug/kdb/kdb_main.c
index 8544d7a55a57..67d9f2403b52 100644
--- a/kernel/debug/kdb/kdb_main.c
+++ b/kernel/debug/kdb/kdb_main.c
@@ -2126,8 +2126,8 @@ static int kdb_dmesg(int argc, const char **argv)
 		kdb_set(2, setargs);
 	}
 
-	kmsg_dump_rewind_nolock(&iter);
-	while (kmsg_dump_get_line_nolock(&iter, 1, NULL, 0, NULL))
+	kmsg_dump_rewind(&iter);
+	while (kmsg_dump_get_line(&iter, 1, NULL, 0, NULL))
 		n++;
 
 	if (lines < 0) {
@@ -2159,8 +2159,8 @@ static int kdb_dmesg(int argc, const char **argv)
 	if (skip >= n || skip < 0)
 		return 0;
 
-	kmsg_dump_rewind_nolock(&iter);
-	while (kmsg_dump_get_line_nolock(&iter, 1, buf, sizeof(buf), &len)) {
+	kmsg_dump_rewind(&iter);
+	while (kmsg_dump_get_line(&iter, 1, buf, sizeof(buf), &len)) {
 		if (skip) {
 			skip--;
 			continue;
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 8994bc192b88..602de86d4e76 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -3373,7 +3373,7 @@ void kmsg_dump(enum kmsg_dump_reason reason)
 }
 
 /**
- * kmsg_dump_get_line_nolock - retrieve one kmsg log line (unlocked version)
+ * kmsg_dump_get_line - retrieve one kmsg log line
  * @iter: kmsg dump iterator
  * @syslog: include the "<4>" prefixes
  * @line: buffer to copy the line to
@@ -3388,22 +3388,22 @@ 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_nolock(struct kmsg_dump_iter *iter, bool syslog,
-			       char *line, size_t size, size_t *len)
+bool kmsg_dump_get_line(struct kmsg_dump_iter *iter, bool syslog,
+			char *line, size_t size, size_t *len)
 {
 	u64 min_seq = latched_seq_read_nolock(&clear_seq);
 	struct printk_info info;
 	unsigned int line_count;
 	struct printk_record r;
+	unsigned long flags;
 	size_t l = 0;
 	bool ret = false;
 
 	if (iter->cur_seq < min_seq)
 		iter->cur_seq = min_seq;
 
+	printk_safe_enter_irqsave(flags);
 	prb_rec_init_rd(&r, &info, line, size);
 
 	/* Read text or count text lines? */
@@ -3424,40 +3424,11 @@ bool kmsg_dump_get_line_nolock(struct kmsg_dump_iter *iter, bool syslog,
 	iter->cur_seq = r.info->seq + 1;
 	ret = true;
 out:
+	printk_safe_exit_irqrestore(flags);
 	if (len)
 		*len = l;
 	return ret;
 }
-
-/**
- * kmsg_dump_get_line - retrieve one kmsg log line
- * @iter: kmsg dump iterator
- * @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_dump_iter *iter, bool syslog,
-			char *line, size_t size, size_t *len)
-{
-	unsigned long flags;
-	bool ret;
-
-	printk_safe_enter_irqsave(flags);
-	ret = kmsg_dump_get_line_nolock(iter, syslog, line, size, len);
-	printk_safe_exit_irqrestore(flags);
-
-	return ret;
-}
 EXPORT_SYMBOL_GPL(kmsg_dump_get_line);
 
 /**
@@ -3550,22 +3521,6 @@ bool kmsg_dump_get_buffer(struct kmsg_dump_iter *iter, bool syslog,
 }
 EXPORT_SYMBOL_GPL(kmsg_dump_get_buffer);
 
-/**
- * kmsg_dump_rewind_nolock - reset the iterator (unlocked version)
- * @iter: kmsg dump iterator
- *
- * 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_dump_iter *iter)
-{
-	iter->cur_seq = latched_seq_read_nolock(&clear_seq);
-	iter->next_seq = prb_next_seq(prb);
-}
-
 /**
  * kmsg_dump_rewind - reset the iterator
  * @iter: kmsg dump iterator
@@ -3579,7 +3534,8 @@ void kmsg_dump_rewind(struct kmsg_dump_iter *iter)
 	unsigned long flags;
 
 	printk_safe_enter_irqsave(flags);
-	kmsg_dump_rewind_nolock(iter);
+	iter->cur_seq = latched_seq_read_nolock(&clear_seq);
+	iter->next_seq = prb_next_seq(prb);
 	printk_safe_exit_irqrestore(flags);
 }
 EXPORT_SYMBOL_GPL(kmsg_dump_rewind);
-- 
2.20.1

lkml delivery: was: Re: [PATCH next v4 00/15] printk: remove logbuf_lock

[Petr Mladek]

Hi John,

On Wed 2021-03-03 11:15:13, John Ogness wrote:
> Hello,
> 
> Here is v4 of a series to remove @logbuf_lock, exposing the
> ringbuffer locklessly to both readers and writers. v3 is
> here [0].

Have you got some reply from lkml that it has not delivered there,
please?

I am not able to get the patchset using b4 tool:

$> b4 am -o test 20210303101528.29901-1-john.ogness@linutronix.de
Looking up https://lore.kernel.org/r/20210303101528.29901-1-john.ogness%40linutronix.de
Grabbing thread from lore.kernel.org/linux-hyperv
Analyzing 2 messages in the thread
---
Thread incomplete, attempting to backfill
Grabbing thread from lore.kernel.org/lkml
Server returned an error: 404
Grabbing thread from lore.kernel.org/linux-mtd
Server returned an error: 404
Grabbing thread from lore.kernel.org/linuxppc-dev
Loaded 2 messages from https://lore.kernel.org/linuxppc-dev/
---
Writing test/v4_20210303_john_ogness_printk_remove_logbuf_lock.mbx
  ERROR: missing [1/15]!
  ERROR: missing [2/15]!
  ERROR: missing [3/15]!
  ERROR: missing [4/15]!
  ERROR: missing [5/15]!
  ERROR: missing [6/15]!
  ERROR: missing [7/15]!
  ERROR: missing [8/15]!
  ERROR: missing [9/15]!
  ERROR: missing [10/15]!
  [PATCH next v4 11/15] printk: kmsg_dumper: remove @active field
  ✓ [PATCH next v4 12/15] printk: introduce a kmsg_dump iterator
  ERROR: missing [13/15]!
  [PATCH next v4 14/15] printk: kmsg_dump: remove _nolock() variants
  ERROR: missing [15/15]!
---
Total patches: 3
---
WARNING: Thread incomplete!
Cover: test/v4_20210303_john_ogness_printk_remove_logbuf_lock.cover
 Link: https://lore.kernel.org/r/20210303101528.29901-1-john.ogness@linutronix.de
 Base: not found
       git am test/v4_20210303_john_ogness_printk_remove_logbuf_lock.mbx


and I do not see it at lore. It has only found copies in linux-hyperv
and linux-ppcdev mailing lists,
see https://lore.kernel.org/lkml/20210303101528.29901-2-john.ogness@linutronix.de/

Best Regards,
Petr

Re: [PATCH next v4 12/15] printk: introduce a kmsg_dump iterator

[Petr Mladek]

On Wed 2021-03-03 11:15:25, John Ogness wrote:
> Rather than storing the iterator information in the registered
> kmsg_dumper structure, create a separate iterator structure. The
> kmsg_dump_iter structure can reside on the stack of the caller, thus
> allowing lockless use of the kmsg_dump functions.
> 
> Update code that accesses the kernel logs using the kmsg_dumper
> structure to use the new kmsg_dump_iter structure. For kmsg_dumpers,
> this also means adding a call to kmsg_dump_rewind() to initialize
> the iterator.
> 
> All this is in preparation for removal of @logbuf_lock.
> 
> Signed-off-by: John Ogness <john.ogness@linutronix.de>
> Reviewed-by: Kees Cook <keescook@chromium.org> # pstore

Reviewed-by: Petr Mladek <pmladek@suse.com>

Best Regards,
Petr

Re: lkml delivery: was: Re: [PATCH next v4 00/15] printk: remove logbuf_lock

[Steven Rostedt]

On Wed, 3 Mar 2021 14:18:29 +0100
Petr Mladek <pmladek@suse.com> wrote:

> Hi John,
> 
> On Wed 2021-03-03 11:15:13, John Ogness wrote:
> > Hello,
> > 
> > Here is v4 of a series to remove @logbuf_lock, exposing the
> > ringbuffer locklessly to both readers and writers. v3 is
> > here [0].  
> 
> Have you got some reply from lkml that it has not delivered there,
> please?

vger has been having some issues as of late, and emails have been coming in
slowly. I just received emails I sent more than 24 hours a head of time.
Those in charge are trying to work things out.

-- Steve

Re: [PATCH next v4 00/15] printk: remove logbuf_lock

[Petr Mladek]

On Wed 2021-03-03 11:15:13, John Ogness wrote:
> Hello,
> 
> Here is v4 of a series to remove @logbuf_lock, exposing the
> ringbuffer locklessly to both readers and writers. v3 is
> here [0].

The series look ready. I am going to push it into printk/linux.git
the following week unless anyone speaks against it in the meantime.

Best Regards,
Petr

Re: [PATCH next v4 00/15] printk: remove logbuf_lock

[Petr Mladek]

On Wed 2021-03-03 16:34:19, Petr Mladek wrote:
> On Wed 2021-03-03 11:15:13, John Ogness wrote:
> > Hello,
> > 
> > Here is v4 of a series to remove @logbuf_lock, exposing the
> > ringbuffer locklessly to both readers and writers. v3 is
> > here [0].
> 
> The series look ready. I am going to push it into printk/linux.git
> the following week unless anyone speaks against it in the meantime.

The series is committed in printk/linux.git, branch printk-rework.

Best Regards,
Petr