[PATCH next v3 12/15] printk: introduce a kmsg_dump iterator

John Ogness
2021-02-25T20:24:35Z

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.

This change also means that the kmsg_dumper dump() callback no
longer needs to pass in the kmsg_dumper as an argument. If
kmsg_dumpers want to access the kernel logs, they can use the new
iterator.

Update the kmsg_dumper callback prototype. 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>
---
arch/powerpc/kernel/nvram_64.c | 14 +++---
arch/powerpc/platforms/powernv/opal-kmsg.c | 3 +-
arch/powerpc/xmon/xmon.c | 6 +--
arch/um/kernel/kmsg_dump.c | 8 +--
drivers/hv/vmbus_drv.c | 7 +--
drivers/mtd/mtdoops.c | 8 +--
fs/pstore/platform.c | 8 +--
include/linux/kmsg_dump.h | 38 ++++++++-------
kernel/debug/kdb/kdb_main.c | 10 ++--
kernel/printk/printk.c | 57 ++++++++++------------
10 files changed, 81 insertions(+), 78 deletions(-)

diff --git a/arch/powerpc/kernel/nvram_64.c b/arch/powerpc/kernel/nvram_64.c
index 532f22637783..5a64b24a91c2 100644
--- a/arch/powerpc/kernel/nvram_64.c
+++ b/arch/powerpc/kernel/nvram_64.c
@@ -72,8 +72,7 @@ static const char *nvram_os_partitions[] = {
NULL
};

-static void oops_to_nvram(struct kmsg_dumper *dumper,
- enum kmsg_dump_reason reason);
+static void oops_to_nvram(enum kmsg_dump_reason reason);

static struct kmsg_dumper nvram_kmsg_dumper = {
.dump = oops_to_nvram
@@ -642,11 +641,11 @@ void __init nvram_init_oops_partition(int rtas_partition_exists)
* that we think will compress sufficiently to fit in the lnx,oops-log
* partition. If that's too much, go back and capture uncompressed text.
*/
-static void oops_to_nvram(struct kmsg_dumper *dumper,
- enum kmsg_dump_reason reason)
+static void oops_to_nvram(enum kmsg_dump_reason reason)
{
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 +680,14 @@ 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/platforms/powernv/opal-kmsg.c b/arch/powerpc/platforms/powernv/opal-kmsg.c
index 6c3bc4b4da98..a7bd6ac681f4 100644
--- a/arch/powerpc/platforms/powernv/opal-kmsg.c
+++ b/arch/powerpc/platforms/powernv/opal-kmsg.c
@@ -19,8 +19,7 @@
* may not be completely printed. This function does not actually dump the
* message, it just ensures that OPAL completely flushes the console buffer.
*/
-static void kmsg_dump_opal_console_flush(struct kmsg_dumper *dumper,
- enum kmsg_dump_reason reason)
+static void kmsg_dump_opal_console_flush(enum kmsg_dump_reason reason)
{
/*
* Outside of a panic context the pollers will continue to run,
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 4869e2cc787c..9fbc5e5b1023 100644
--- a/arch/um/kernel/kmsg_dump.c
+++ b/arch/um/kernel/kmsg_dump.c
@@ -7,9 +7,9 @@
#include <shared/kern.h>
#include <os.h>

-static void kmsg_dumper_stdout(struct kmsg_dumper *dumper,
- enum kmsg_dump_reason reason)
+static void kmsg_dumper_stdout(enum kmsg_dump_reason reason)
{
+ static struct kmsg_dump_iter iter;
static DEFINE_SPINLOCK(lock);
static char line[1024];
struct console *con;
@@ -34,8 +34,10 @@ static void kmsg_dumper_stdout(struct kmsg_dumper *dumper,
if (!spin_trylock(&lock))
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..1b858f280e22 100644
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -1388,9 +1388,9 @@ static void vmbus_isr(void)
* Callback from kmsg_dump. Grab as much as possible from the end of the kmsg
* buffer and call into Hyper-V to transfer the data.
*/
-static void hv_kmsg_dump(struct kmsg_dumper *dumper,
- enum kmsg_dump_reason reason)
+static void hv_kmsg_dump(enum kmsg_dump_reason reason)
{
+ struct kmsg_dump_iter iter;
size_t bytes_written;
phys_addr_t panic_pa;

@@ -1404,7 +1404,8 @@ 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..d179b726a1c9 100644
--- a/drivers/mtd/mtdoops.c
+++ b/drivers/mtd/mtdoops.c
@@ -272,19 +272,21 @@ static void find_next_position(struct mtdoops_context *cxt)
mtdoops_inc_counter(cxt);
}

-static void mtdoops_do_dump(struct kmsg_dumper *dumper,
- enum kmsg_dump_reason reason)
+static void mtdoops_do_dump(enum kmsg_dump_reason reason)
{
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..edfc9504e024 100644
--- a/fs/pstore/platform.c
+++ b/fs/pstore/platform.c
@@ -382,9 +382,9 @@ void pstore_record_init(struct pstore_record *record,
* callback from kmsg_dump. Save as much as we can (up to kmsg_bytes) from the
* end of the buffer.
*/
-static void pstore_dump(struct kmsg_dumper *dumper,
- enum kmsg_dump_reason reason)
+static void pstore_dump(enum kmsg_dump_reason reason)
{
+ struct kmsg_dump_iter iter;
unsigned long total = 0;
const char *why;
unsigned int part = 1;
@@ -405,6 +405,8 @@ static void pstore_dump(struct kmsg_dumper *dumper,
}
}

+ kmsg_dump_rewind(&iter);
+
oopscount++;
while (total < kmsg_bytes) {
char *dst;
@@ -435,7 +437,7 @@ 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..5d3bf20f9f0a 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);
+ void (*dump)(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 45cb3e9c62c5..e58ccc368348 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) {
@@ -3407,21 +3406,15 @@ 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);
+ dumper->dump(reason);
}
rcu_read_unlock();
}

/**
* 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
@@ -3438,7 +3431,7 @@ 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)
{
struct printk_info info;
@@ -3451,11 +3444,11 @@ bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,

/* 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 +3457,7 @@ 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 +3467,7 @@ 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 +3482,14 @@ 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 +3498,7 @@ 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
@@ -3522,7 +3515,7 @@ 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)
{
struct printk_info info;
@@ -3538,15 +3531,15 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
goto out;

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 +3550,7 @@ 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 +3563,7 @@ 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 +3572,7 @@ 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 +3584,7 @@ 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 +3592,26 @@ 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