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[RFC v3 0/9] Additional kmsg devices

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  [RFC v3 0/9] Additional kmsg devices Paul Osmialowski <p.osmialowsk@samsung.com> - 2015-10-19 15:10 +0200
    [RFC v3 6/9] kmsg: add ioctl for adding and deleting kmsg* devices Paul Osmialowski <p.osmialowsk@samsung.com> - 2015-10-19 15:10 +0200
      Re: [RFC v3 6/9] kmsg: add ioctl for adding and deleting kmsg* devices Arnd Bergmann <arnd@arndb.de> - 2015-10-19 15:20 +0200
    [RFC v3 5/9] kmsg: add function for adding and deleting additional  buffers Paul Osmialowski <p.osmialowsk@samsung.com> - 2015-10-19 15:20 +0200
      Re: [RFC v3 5/9] kmsg: add function for adding and deleting  additional buffers kbuild test robot <lkp@intel.com> - 2015-10-19 20:30 +0200
    Re: [RFC v3 0/9] Additional kmsg devices Richard Weinberger <richard.weinberger@gmail.com> - 2015-10-19 15:30 +0200

#1250651 — [RFC v3 0/9] Additional kmsg devices

Dear All,

This is the third iteration of Marcin Niesluchowski's serie of patches
extending kmsg interface with ability to dynamically create (and destroy)
kmsg-like devices which can be used by userspace for logging.

In this iteration, following Joe Perches's suggestion, I've extracted
kmsg related functions from printk.c to a new file, kmsg.c.

Best regards,
Paul

Marcin Niesluchowski (7):
  printk: add one function for storing log in proper format
  kmsg: introduce additional kmsg devices support
  kmsg: add additional buffers support to memory class
  kmsg: add function for adding and deleting additional buffers
  kmsg: add ioctl for adding and deleting kmsg* devices
  kmsg: add ioctl for kmsg* devices operating on buffers
  kmsg: add predefined _PID, _TID, _COMM keywords to kmsg* log dict

Paul Osmialowski (2):
  printk: extract kmsg-related routines from printk.c to kmsg.c
  kmsg: selftests

 Documentation/ioctl/ioctl-number.txt               |    1 +
 drivers/char/mem.c                                 |   27 +-
 fs/proc/kmsg.c                                     |    4 +-
 include/linux/printk.h                             |   48 +
 include/uapi/linux/Kbuild                          |    1 +
 include/uapi/linux/kmsg_ioctl.h                    |   45 +
 kernel/printk/Makefile                             |    1 +
 kernel/printk/kmsg.c                               | 1054 +++++++++++++++++
 kernel/printk/printk.c                             | 1250 +++++---------------
 kernel/printk/printk.h                             |  247 ++++
 samples/kmsg/kmsg-api.h                            |   44 +
 tools/testing/selftests/Makefile                   |    1 +
 tools/testing/selftests/kmsg/.gitignore            |    1 +
 tools/testing/selftests/kmsg/Makefile              |   30 +
 tools/testing/selftests/kmsg/kmsg-test.c           |  329 ++++++
 tools/testing/selftests/kmsg/kmsg-test.h           |   34 +
 tools/testing/selftests/kmsg/test-buffer-add-del.c |   76 ++
 .../kmsg/test-buffer-add-write-read-del.c          |  161 +++
 .../kmsg/test-buffer-buf-multithreaded-torture.c   |  199 ++++
 .../selftests/kmsg/test-buffer-buf-torture.c       |  139 +++
 20 files changed, 2729 insertions(+), 963 deletions(-)
 create mode 100644 include/uapi/linux/kmsg_ioctl.h
 create mode 100644 kernel/printk/kmsg.c
 create mode 100644 kernel/printk/printk.h
 create mode 100644 samples/kmsg/kmsg-api.h
 create mode 100644 tools/testing/selftests/kmsg/.gitignore
 create mode 100644 tools/testing/selftests/kmsg/Makefile
 create mode 100644 tools/testing/selftests/kmsg/kmsg-test.c
 create mode 100644 tools/testing/selftests/kmsg/kmsg-test.h
 create mode 100644 tools/testing/selftests/kmsg/test-buffer-add-del.c
 create mode 100644 tools/testing/selftests/kmsg/test-buffer-add-write-read-del.c
 create mode 100644 tools/testing/selftests/kmsg/test-buffer-buf-multithreaded-torture.c
 create mode 100644 tools/testing/selftests/kmsg/test-buffer-buf-torture.c

-- 
1.9.1

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#1250655 — [RFC v3 6/9] kmsg: add ioctl for adding and deleting kmsg* devices

From: Marcin Niesluchowski <m.niesluchow@samsung.com>

There is no possibility to add/delete kmsg* buffers from userspace.

Adds following ioctl for main kmsg device adding and deleting
additional kmsg devices:
* KMSG_CMD_BUFFER_ADD
* KMSG_CMD_BUFFER_DEL

Signed-off-by: Marcin Niesluchowski <m.niesluchow@samsung.com>
Signed-off-by: Paul Osmialowski <p.osmialowsk@samsung.com>
---
 Documentation/ioctl/ioctl-number.txt |   1 +
 drivers/char/mem.c                   |   2 +-
 include/linux/printk.h               |   7 ++
 include/uapi/linux/Kbuild            |   1 +
 include/uapi/linux/kmsg_ioctl.h      |  30 +++++++++
 kernel/printk/kmsg.c                 | 123 +++++++++++++++++++++++++++++++++++
 6 files changed, 163 insertions(+), 1 deletion(-)
 create mode 100644 include/uapi/linux/kmsg_ioctl.h

diff --git a/Documentation/ioctl/ioctl-number.txt b/Documentation/ioctl/ioctl-number.txt
index 43e6923..76dec8b 100644
--- a/Documentation/ioctl/ioctl-number.txt
+++ b/Documentation/ioctl/ioctl-number.txt
@@ -319,6 +319,7 @@ Code  Seq#(hex)	Include File		Comments
 					<mailto:vgo@ratio.de>
 0xB1	00-1F	PPPoX			<mailto:mostrows@styx.uwaterloo.ca>
 0xB3	00	linux/mmc/ioctl.h
+0xBB	00-02	uapi/linux/kmsg_ioctl.h
 0xC0	00-0F	linux/usb/iowarrior.h
 0xCA	00-0F	uapi/misc/cxl.h
 0xCA	80-8F	uapi/scsi/cxlflash_ioctl.h
diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index 7d46234..ac824de 100644
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -808,7 +808,7 @@ static int memory_open(struct inode *inode, struct file *filp)
 
 	minor = iminor(inode);
 	if (minor >= ARRAY_SIZE(devlist))
-		return kmsg_memory_open(inode, filp);
+		return kmsg_memory_open_ext(inode, filp);
 
 	dev = &devlist[minor];
 	if (!dev->fops)
diff --git a/include/linux/printk.h b/include/linux/printk.h
index 35111e8..294adab 100644
--- a/include/linux/printk.h
+++ b/include/linux/printk.h
@@ -427,9 +427,11 @@ extern struct class *mem_class;
 #define KMSG_MINOR	11
 
 extern const struct file_operations kmsg_fops;
+extern const struct file_operations kmsg_fops_ext;
 
 extern struct device *init_kmsg(int minor, umode_t mode);
 extern int kmsg_memory_open(struct inode *inode, struct file *filp);
+extern int kmsg_memory_open_ext(struct inode *inode, struct file *filp);
 extern int kmsg_mode(int minor, umode_t *mode);
 extern int kmsg_sys_buffer_add(size_t size, umode_t mode);
 extern void kmsg_sys_buffer_del(int minor);
@@ -446,6 +448,11 @@ static inline int kmsg_memory_open(struct inode *inode, struct file *filp)
 	return -ENXIO;
 }
 
+static inline int kmsg_memory_open_ext(struct inode *inode, struct file *filp)
+{
+	return -ENXIO;
+}
+
 static inline int kmsg_mode(int minor, umode_t *mode)
 {
 	return -ENXIO;
diff --git a/include/uapi/linux/Kbuild b/include/uapi/linux/Kbuild
index e777078..d998999 100644
--- a/include/uapi/linux/Kbuild
+++ b/include/uapi/linux/Kbuild
@@ -225,6 +225,7 @@ header-y += kernel-page-flags.h
 header-y += kexec.h
 header-y += keyboard.h
 header-y += keyctl.h
+header-y += kmsg_ioctl.h
 
 ifneq ($(wildcard $(srctree)/arch/$(SRCARCH)/include/uapi/asm/kvm.h \
 		  $(srctree)/arch/$(SRCARCH)/include/asm/kvm.h),)
diff --git a/include/uapi/linux/kmsg_ioctl.h b/include/uapi/linux/kmsg_ioctl.h
new file mode 100644
index 0000000..89c0c61
--- /dev/null
+++ b/include/uapi/linux/kmsg_ioctl.h
@@ -0,0 +1,30 @@
+/*
+ * This is ioctl include for kmsg* devices
+ */
+
+#ifndef _KMSG_IOCTL_H_
+#define _KMSG_IOCTL_H_
+
+#include <linux/ioctl.h>
+#include <linux/types.h>
+
+struct kmsg_cmd_buffer_add {
+	size_t size;
+	unsigned short mode;
+	int minor;
+} __attribute__((packed));
+
+#define KMSG_IOCTL_MAGIC	0xBB
+
+/*
+ * A ioctl interface for kmsg device.
+ *
+ * KMSG_CMD_BUFFER_ADD:	Creates additional kmsg device based on its size
+ *			and mode. Minor of created device is put.
+ * KMSG_CMD_BUFFER_DEL:	Removes additional kmsg device based on its minor
+ */
+#define KMSG_CMD_BUFFER_ADD		_IOWR(KMSG_IOCTL_MAGIC, 0x00, \
+					      struct kmsg_cmd_buffer_add)
+#define KMSG_CMD_BUFFER_DEL		_IOW(KMSG_IOCTL_MAGIC, 0x01, int)
+
+#endif
diff --git a/kernel/printk/kmsg.c b/kernel/printk/kmsg.c
index 184575b..f91a64a 100644
--- a/kernel/printk/kmsg.c
+++ b/kernel/printk/kmsg.c
@@ -22,8 +22,12 @@
 
 #include <asm/uaccess.h>
 
+#include <uapi/linux/kmsg_ioctl.h>
+
 #include "printk.h"
 
+#define KMSG_MAX_MINOR_LEN	20
+
 /* /dev/kmsg - userspace message inject/listen interface */
 struct devkmsg_user {
 	u64 seq;
@@ -407,6 +411,118 @@ const struct file_operations kmsg_fops = {
 	.release = devkmsg_release,
 };
 
+static int kmsg_open_ext(struct inode *inode, struct file *file)
+{
+	return kmsg_fops.open(inode, file);
+}
+
+static ssize_t kmsg_write_iter_ext(struct kiocb *iocb, struct iov_iter *from)
+{
+	return kmsg_fops.write_iter(iocb, from);
+}
+
+static ssize_t kmsg_read_ext(struct file *file, char __user *buf,
+			     size_t count, loff_t *ppos)
+{
+	return kmsg_fops.read(file, buf, count, ppos);
+}
+
+static loff_t kmsg_llseek_ext(struct file *file, loff_t offset, int whence)
+{
+	return kmsg_fops.llseek(file, offset, whence);
+}
+
+static unsigned int kmsg_poll_ext(struct file *file,
+				  struct poll_table_struct *wait)
+{
+	return kmsg_fops.poll(file, wait);
+}
+
+static long kmsg_ioctl_buffers(struct file *file, unsigned int cmd,
+			       unsigned long arg)
+{
+	void __user *argp = (void __user *)arg;
+	size_t size;
+	umode_t mode;
+	char name[4 + KMSG_MAX_MINOR_LEN + 1];
+	struct device *dev;
+	int minor;
+
+	if (iminor(file->f_inode) != log_buf.minor)
+		return -ENOTTY;
+
+	switch (cmd) {
+	case KMSG_CMD_BUFFER_ADD:
+		if (copy_from_user(&size, argp, sizeof(size)))
+			return -EFAULT;
+		argp += sizeof(size);
+		if (copy_from_user(&mode, argp, sizeof(mode)))
+			return -EFAULT;
+		argp += sizeof(mode);
+		minor = kmsg_sys_buffer_add(size, mode);
+		if (minor < 0)
+			return minor;
+		sprintf(name, "kmsg%d", minor);
+		dev = device_create(mem_class, NULL, MKDEV(MEM_MAJOR, minor),
+				    NULL, name);
+		if (IS_ERR(dev)) {
+			kmsg_sys_buffer_del(minor);
+			return PTR_ERR(dev);
+		}
+		if (copy_to_user(argp, &minor, sizeof(minor))) {
+			device_destroy(mem_class, MKDEV(MEM_MAJOR, minor));
+			kmsg_sys_buffer_del(minor);
+			return -EFAULT;
+		}
+		return 0;
+	case KMSG_CMD_BUFFER_DEL:
+		if (copy_from_user(&minor, argp, sizeof(minor)))
+			return -EFAULT;
+		if (minor <= log_buf.minor)
+			return -EINVAL;
+		device_destroy(mem_class, MKDEV(MEM_MAJOR, minor));
+		kmsg_sys_buffer_del(minor);
+		return 0;
+	}
+	return -ENOTTY;
+}
+
+static long kmsg_unlocked_ioctl_ext(struct file *file, unsigned int cmd,
+				    unsigned long arg)
+{
+	long ret = kmsg_ioctl_buffers(file, cmd, arg);
+
+	if (ret == -ENOTTY)
+		return kmsg_fops.unlocked_ioctl(file, cmd, arg);
+	return ret;
+}
+
+static long kmsg_compat_ioctl_ext(struct file *file, unsigned int cmd,
+				  unsigned long arg)
+{
+	long ret = kmsg_ioctl_buffers(file, cmd, arg);
+
+	if (ret == -ENOTTY)
+		return kmsg_fops.compat_ioctl(file, cmd, arg);
+	return ret;
+}
+
+static int kmsg_release_ext(struct inode *inode, struct file *file)
+{
+	return kmsg_fops.release(inode, file);
+}
+
+const struct file_operations kmsg_fops_ext = {
+	.open		= kmsg_open_ext,
+	.read		= kmsg_read_ext,
+	.write_iter	= kmsg_write_iter_ext,
+	.llseek		= kmsg_llseek_ext,
+	.poll		= kmsg_poll_ext,
+	.unlocked_ioctl	= kmsg_unlocked_ioctl_ext,
+	.compat_ioctl	= kmsg_compat_ioctl_ext,
+	.release	= kmsg_release_ext,
+};
+
 /* Should be used for device registration */
 struct device *init_kmsg(int minor, umode_t mode)
 {
@@ -423,6 +539,13 @@ int kmsg_memory_open(struct inode *inode, struct file *filp)
 	return kmsg_fops.open(inode, filp);
 }
 
+int kmsg_memory_open_ext(struct inode *inode, struct file *filp)
+{
+	filp->f_op = &kmsg_fops_ext;
+
+	return kmsg_fops_ext.open(inode, filp);
+}
+
 int kmsg_mode(int minor, umode_t *mode)
 {
 	int ret = -ENXIO;
-- 
1.9.1

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#1250675 — Re: [RFC v3 6/9] kmsg: add ioctl for adding and deleting kmsg* devices

On Monday 19 October 2015 14:58:20 Paul Osmialowski wrote:
> +
> +struct kmsg_cmd_buffer_add {
> +       size_t size;
> +       unsigned short mode;
> +       int minor;
> +} __attribute__((packed));
> +
> +#define KMSG_IOCTL_MAGIC       0xBB
> +
> +/*
> 

Try to avoid using packed unaligned data structures. Here I would
just use __u64 and __u32 members.

> +       case KMSG_CMD_BUFFER_ADD:
> +               if (copy_from_user(&size, argp, sizeof(size)))
> +                       return -EFAULT;
> +               argp += sizeof(size);
> +               if (copy_from_user(&mode, argp, sizeof(mode)))
> +                       return -EFAULT;

This is a rather unusual way to access the data. Just copy the
entire structure to the stack.

	Arnd
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#1250667 — [RFC v3 5/9] kmsg: add function for adding and deleting additional buffers

From: Marcin Niesluchowski <m.niesluchow@samsung.com>

Additional kmsg buffers should be created and deleted dynamically.

Adding two functions
* kmsg_sys_buffer_add() creates additional kmsg buffer returning minor
* kmsg_sys_buffer_del() deletes one based on provided minor

Signed-off-by: Marcin Niesluchowski <m.niesluchow@samsung.com>
Signed-off-by: Paul Osmialowski <p.osmialowsk@samsung.com>
---
 include/linux/printk.h |   9 +++++
 kernel/printk/kmsg.c   | 107 +++++++++++++++++++++++++++++++++++++++++++++++--
 kernel/printk/printk.c |  12 ++++++
 kernel/printk/printk.h |   4 ++
 4 files changed, 129 insertions(+), 3 deletions(-)

diff --git a/include/linux/printk.h b/include/linux/printk.h
index 67840e0..35111e8 100644
--- a/include/linux/printk.h
+++ b/include/linux/printk.h
@@ -431,6 +431,8 @@ extern const struct file_operations kmsg_fops;
 extern struct device *init_kmsg(int minor, umode_t mode);
 extern int kmsg_memory_open(struct inode *inode, struct file *filp);
 extern int kmsg_mode(int minor, umode_t *mode);
+extern int kmsg_sys_buffer_add(size_t size, umode_t mode);
+extern void kmsg_sys_buffer_del(int minor);
 
 #else
 
@@ -449,6 +451,13 @@ static inline int kmsg_mode(int minor, umode_t *mode)
 	return -ENXIO;
 }
 
+static inline int kmsg_sys_buffer_add(size_t size, umode_t mode)
+{
+	return -ENXIO;
+}
+
+static inline void kmsg_sys_buffer_del(int minor) {}
+
 #endif
 
 enum {
diff --git a/kernel/printk/kmsg.c b/kernel/printk/kmsg.c
index 7fcd628..184575b 100644
--- a/kernel/printk/kmsg.c
+++ b/kernel/printk/kmsg.c
@@ -18,6 +18,7 @@
 #include <linux/device.h>
 #include <linux/major.h>
 #include <linux/kdev_t.h>
+#include <linux/kref.h>
 
 #include <asm/uaccess.h>
 
@@ -140,8 +141,20 @@ static ssize_t kmsg_read(struct log_buffer *log_b, struct file *file,
 		}
 
 		raw_spin_unlock_irq(&log_b->lock);
-		ret = wait_event_interruptible(log_b->wait,
-					       user->seq != log_b->next_seq);
+		if (log_b == &log_buf) {
+			ret = wait_event_interruptible(log_b->wait,
+						user->seq != log_b->next_seq);
+		} else {
+			rcu_read_unlock();
+			kref_get(&log_b->refcount);
+			ret = wait_event_interruptible(log_b->wait,
+						user->seq != log_b->next_seq);
+			if (log_b->minor == -1)
+				ret = -ENXIO;
+			if (kref_put(&log_b->refcount, log_buf_release))
+				ret = -ENXIO;
+			rcu_read_lock();
+		}
 		if (ret)
 			goto out;
 		raw_spin_lock_irq(&log_b->lock);
@@ -310,8 +323,14 @@ static unsigned int devkmsg_poll(struct file *file, poll_table *wait)
 	rcu_read_lock();
 	list_for_each_entry_rcu(log_b, &log_buf.list, list) {
 		if (log_b->minor == minor) {
+			kref_get(&log_b->refcount);
+			rcu_read_unlock();
+
 			ret = kmsg_poll(log_b, file, wait);
-			break;
+
+			if (kref_put(&log_b->refcount, log_buf_release))
+				return POLLERR|POLLNVAL;
+			return ret;
 		}
 	}
 	rcu_read_unlock();
@@ -427,6 +446,88 @@ int kmsg_mode(int minor, umode_t *mode)
 	return ret;
 }
 
+static DEFINE_SPINLOCK(kmsg_sys_list_lock);
+
+int kmsg_sys_buffer_add(size_t size, umode_t mode)
+{
+	unsigned long flags;
+	int minor = log_buf.minor;
+	struct log_buffer *log_b;
+	struct log_buffer *log_b_new;
+
+	if (size < LOG_LINE_MAX + PREFIX_MAX)
+		return -EINVAL;
+
+	log_b_new = kzalloc(sizeof(struct log_buffer), GFP_KERNEL);
+	if (!log_b_new)
+		return -ENOMEM;
+
+	log_b_new->buf = kmalloc(size, GFP_KERNEL);
+	if (!log_b_new->buf) {
+		kfree(log_b_new);
+		return -ENOMEM;
+	}
+
+	log_b_new->len = size;
+	log_b_new->lock = __RAW_SPIN_LOCK_UNLOCKED(log_b_new->lock);
+	init_waitqueue_head(&log_b_new->wait);
+	kref_init(&log_b_new->refcount);
+	log_b_new->mode = mode;
+
+	kref_get(&log_b_new->refcount);
+
+	spin_lock_irqsave(&kmsg_sys_list_lock, flags);
+
+	list_for_each_entry(log_b, &log_buf.list, list) {
+		if (log_b->minor - minor > 1)
+			break;
+
+		minor = log_b->minor;
+	}
+
+	if (!(minor & MINORMASK)) {
+		kref_put(&log_b->refcount, log_buf_release);
+		spin_unlock_irqrestore(&kmsg_sys_list_lock, flags);
+		return -ERANGE;
+	}
+
+	minor += 1;
+	log_b_new->minor = minor;
+
+	list_add_tail_rcu(&log_b_new->list, &log_b->list);
+
+	spin_unlock_irqrestore(&kmsg_sys_list_lock, flags);
+
+	return minor;
+}
+
+void kmsg_sys_buffer_del(int minor)
+{
+	unsigned long flags;
+	struct log_buffer *log_b;
+
+	spin_lock_irqsave(&kmsg_sys_list_lock, flags);
+
+	list_for_each_entry(log_b, &log_buf.list, list) {
+		if (log_b->minor == minor)
+			break;
+	}
+
+	if (log_b == &log_buf) {
+		spin_unlock_irqrestore(&kmsg_sys_list_lock, flags);
+		return;
+	}
+
+	list_del_rcu(&log_b->list);
+
+	spin_unlock_irqrestore(&kmsg_sys_list_lock, flags);
+
+	log_b->minor = -1;
+	wake_up_interruptible(&log_b->wait);
+
+	kref_put(&log_b->refcount, log_buf_release);
+}
+
 static DEFINE_SPINLOCK(dump_list_lock);
 static LIST_HEAD(dump_list);
 
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index beabebb..cfedbe9 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -41,6 +41,8 @@
 #include <linux/irq_work.h>
 #include <linux/utsname.h>
 #include <linux/ctype.h>
+#include <linux/kref.h>
+#include <linux/slab.h>
 
 #include <asm/uaccess.h>
 
@@ -173,6 +175,7 @@ struct log_buffer log_buf = {
 	.len		= __LOG_BUF_K_LEN,
 	.lock		= __RAW_SPIN_LOCK_UNLOCKED(log_buf.lock),
 	.wait		= __WAIT_QUEUE_HEAD_INITIALIZER(log_buf.wait),
+	.refcount	= { .refcount = { .counter = 0 } },
 	.first_seq	= 0,
 	.first_idx	= 0,
 	.next_seq	= 0,
@@ -218,6 +221,15 @@ u32 log_buf_len_get(void)
 	return log_buf.len;
 }
 
+void log_buf_release(struct kref *ref)
+{
+	struct log_buffer *log_b = container_of(ref, struct log_buffer,
+						refcount);
+
+	kfree(log_b->buf);
+	kfree(log_b);
+}
+
 /*
  * Check whether there is enough free space for the given message.
  *
diff --git a/kernel/printk/printk.h b/kernel/printk/printk.h
index 0755100..64f8878 100644
--- a/kernel/printk/printk.h
+++ b/kernel/printk/printk.h
@@ -5,6 +5,7 @@
 #include <linux/spinlock_types.h>
 #include <linux/types.h>
 #include <linux/wait.h>
+#include <linux/kref.h>
 
 #define PREFIX_MAX		32
 #define LOG_LINE_MAX		(1024 - PREFIX_MAX)
@@ -99,6 +100,7 @@ struct log_buffer {
 	char *buf;		/* cyclic log buffer */
 	u32 len;		/* buffer length */
 	wait_queue_head_t wait;	/* wait queue for kmsg buffer */
+	struct kref refcount;	/* refcount for kmsg_sys buffers */
 #endif
 /*
  * The lock protects kmsg buffer, indices, counters. This can be taken within
@@ -127,6 +129,8 @@ struct log_buffer {
 
 extern struct log_buffer log_buf;
 
+void log_buf_release(struct kref *ref);
+
 ssize_t msg_print_ext_header(char *buf, size_t size,
 				    struct printk_log *msg, u64 seq,
 				    enum log_flags prev_flags);
-- 
1.9.1

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#1250992 — Re: [RFC v3 5/9] kmsg: add function for adding and deleting additional buffers

Hi Marcin,

[auto build test WARNING on next-20151016 -- if it's inappropriate base, please suggest rules for selecting the more suitable base]

url:    https://github.com/0day-ci/linux/commits/Paul-Osmialowski/Additional-kmsg-devices/20151019-211509
reproduce:
        # apt-get install sparse
        make ARCH=x86_64 allmodconfig
        make C=1 CF=-D__CHECK_ENDIAN__


sparse warnings: (new ones prefixed by >>)

>> include/linux/rcupdate.h:915:9: sparse: context imbalance in 'kmsg_read' - unexpected unlock

vim +/kmsg_read +915 include/linux/rcupdate.h

f27bc4873 Paul E. McKenney 2014-05-04  899   * that that preemption never happens within any RCU read-side critical
f27bc4873 Paul E. McKenney 2014-05-04  900   * section whose outermost rcu_read_unlock() is called with irqs disabled.
f27bc4873 Paul E. McKenney 2014-05-04  901   * This approach relies on the fact that rt_mutex_unlock() currently only
f27bc4873 Paul E. McKenney 2014-05-04  902   * acquires irq-disabled locks.
f27bc4873 Paul E. McKenney 2014-05-04  903   *
f27bc4873 Paul E. McKenney 2014-05-04  904   * The second of these two approaches is best in most situations,
f27bc4873 Paul E. McKenney 2014-05-04  905   * however, the first approach can also be useful, at least to those
f27bc4873 Paul E. McKenney 2014-05-04  906   * developers willing to keep abreast of the set of locks acquired by
f27bc4873 Paul E. McKenney 2014-05-04  907   * rt_mutex_unlock().
f27bc4873 Paul E. McKenney 2014-05-04  908   *
3d76c0829 Paul E. McKenney 2009-09-28  909   * See rcu_read_lock() for more information.
3d76c0829 Paul E. McKenney 2009-09-28  910   */
bc33f24bd Paul E. McKenney 2009-08-22  911  static inline void rcu_read_unlock(void)
bc33f24bd Paul E. McKenney 2009-08-22  912  {
f78f5b90c Paul E. McKenney 2015-06-18  913  	RCU_LOCKDEP_WARN(!rcu_is_watching(),
bde23c689 Heiko Carstens   2012-02-01  914  			 "rcu_read_unlock() used illegally while idle");
bc33f24bd Paul E. McKenney 2009-08-22 @915  	__release(RCU);
bc33f24bd Paul E. McKenney 2009-08-22  916  	__rcu_read_unlock();
d24209bb6 Paul E. McKenney 2015-01-21  917  	rcu_lock_release(&rcu_lock_map); /* Keep acq info for rls diags. */
bc33f24bd Paul E. McKenney 2009-08-22  918  }
^1da177e4 Linus Torvalds   2005-04-16  919  
^1da177e4 Linus Torvalds   2005-04-16  920  /**
ca5ecddfa Paul E. McKenney 2010-04-28  921   * rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section
^1da177e4 Linus Torvalds   2005-04-16  922   *
^1da177e4 Linus Torvalds   2005-04-16  923   * This is equivalent of rcu_read_lock(), but to be used when updates

:::::: The code at line 915 was first introduced by commit
:::::: bc33f24bdca8b6e97376e3a182ab69e6cdefa989 rcu: Consolidate sparse and lockdep declarations in include/linux/rcupdate.h

:::::: TO: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
:::::: CC: Ingo Molnar <mingo@elte.hu>

---
0-DAY kernel test infrastructure                Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all                   Intel Corporation
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#1250688

On Mon, Oct 19, 2015 at 2:58 PM, Paul Osmialowski
<p.osmialowsk@samsung.com> wrote:
> Dear All,
>
> This is the third iteration of Marcin Niesluchowski's serie of patches
> extending kmsg interface with ability to dynamically create (and destroy)
> kmsg-like devices which can be used by userspace for logging.
>
> In this iteration, following Joe Perches's suggestion, I've extracted
> kmsg related functions from printk.c to a new file, kmsg.c.
>
> Best regards,
> Paul
>
> Marcin Niesluchowski (7):
>   printk: add one function for storing log in proper format
>   kmsg: introduce additional kmsg devices support
>   kmsg: add additional buffers support to memory class
>   kmsg: add function for adding and deleting additional buffers
>   kmsg: add ioctl for adding and deleting kmsg* devices
>   kmsg: add ioctl for kmsg* devices operating on buffers
>   kmsg: add predefined _PID, _TID, _COMM keywords to kmsg* log dict
>
> Paul Osmialowski (2):
>   printk: extract kmsg-related routines from printk.c to kmsg.c
>   kmsg: selftests

Not CC'ing critical voices it not very nice. 8-)

As I replied to v1 of this series, IHMO we should not encourage
userspace tools to use kmsg as their poor-man's syslog.
Everything what this series does in kernel space can also be done
in userspace.

Just my two cents.

-- 
Thanks,
//richard
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