Re: [RFC PATCH] cmdline: Hide "debug" from /proc/cmdline

Borislav Petkov
2014-04-23T15:15:20Z

Hi Linus,

here's some more massaging of your patch. (Btw, let's start a new
thread).

On Wed, Apr 02, 2014 at 06:47:57PM -0700, Linus Torvalds wrote:
> It's definitely not perfect - if we suppress output, and the process
> then closes the file descriptor rather than continuing to write more,
> you won't get that "suppressed" message. But it's a usable starting
> point for testing and commentary on the actual limits.
>
> So we should probably add reporting about suppressed messages at file
> close time,

see below.

> and we should tweak the limits (for example, perhaps not limit things
> if the buffers are largely empty - which happens at bootup), but on
> the whole I think this is a reasonable thing to do.

Err, help me out here pls, which buffers? Do you mean we should look at
log_buf's fill level?

> Whether it actually fixes the problem that Borislav had is
> questionable, of course. For all I know, systemd debug mode generates
> so much data in *other* ways and then causes feedback loops with the
> kernel debugging that this patch is totally immaterial, and dmesg was
> never the main issue. But unlike the "hide 'debug' from
> /proc/cmdline", I think this patch at least _conceptually_ makes a lot
> of sense, even if systemd gets fixed, so ...

Ok, here's a dirty hack that issues ratelimit messages at release time.
I probably should wrap it nicely in ratelimit_*() accessors instead
of poking directly at ratelimit_state. Yeah, maybe a ratelimit_exit()
wrapper which does all the fun automatically.

Anyway, with it, it looks like this:

[ 3.098474] systemd-fstab-g: 4 callbacks suppressed
[ 9.256317] audit_printk_skb: 108 callbacks suppressed
[ 31.486281] systemd-journal: 464 callbacks suppressed

In dmesg, it basically shuts up:

...
[ 3.603657] systemd-journald[115]: Vacuuming...
[ 3.603666] systemd-journald[115]: Vacuuming done, freed 0 bytes
[ 3.603759] systemd-journald[115]: Assertion 'dual_timestamp_is_set(&e->timestamp)' failed at src/libsystemd/sd-event/sd-event.c:2204, function sd_event_get_now_monotonic(). Ignoring.
[ 3.603759] systemd-journald[115]: Flushing /dev/kmsg...
[ 3.603759] systemd-journald[115]: Assertion 'dual_timestamp_is_set(&e->timestamp)' failed at src/libsystemd/sd-event/sd-event.c:2204, function sd_event_get_now_monotonic(). Ignoring.
[ 3.603759] systemd-journald[115]: Assertion 'dual_timestamp_is_set(&e->timestamp)' failed at src/libsystemd/sd-event/sd-event.c:2204, function sd_event_get_now_monotonic(). Ignoring.
[ 3.603759] systemd-journald[115]: Assertion 'dual_timestamp_is_set(&e->timestamp)' failed at src/libsystemd/sd-event/sd-event.c:2204, function sd_event_get_now_monotonic(). Ignoring.
[ 3.640216] BTRFS info (device sda2): disk space caching is enabled
[ 3.815059] systemd-udevd[142]: starting version 210

and then on shutdown, when it releases kmsg:

...
[ OK ] Stopped target Local File Systems (Pre).
Stopping Remount Root and Kernel File Systems...
[ OK ] Stopped Remount Root and Kernel File Systems.
[ OK ] Reached target Shutdown.
Sending SIGTERM to remaining processes...
[ 31.486281] systemd-journal: 464 callbacks suppressed
[ 32.246116] mtrr: no MTRR for fc000000,400000 found
Sending SIGKILL to remaining processes...
Unmounting file systems.
[ 32.356186] BTRFS info (device sda2): disk space caching is enabled
Unmounting /tmp.
[ 32.392842] BTRFS info (device sda2): disk space caching is enabled
Unmounting /var/log.
...

Comments?

Thanks.

---
diff --git a/include/linux/ratelimit.h b/include/linux/ratelimit.h
index 0a260d8a18bf..ab8d9fb76789 100644
--- a/include/linux/ratelimit.h
+++ b/include/linux/ratelimit.h
@@ -7,6 +7,8 @@
#define DEFAULT_RATELIMIT_INTERVAL (5 * HZ)
#define DEFAULT_RATELIMIT_BURST 10

+#define RATELIMIT_MSG_ON_RELEASE BIT(0)
+
struct ratelimit_state {
raw_spinlock_t lock; /* protect the state */

@@ -15,6 +17,7 @@ struct ratelimit_state {
int printed;
int missed;
unsigned long begin;
+ unsigned long flags;
};

#define DEFINE_RATELIMIT_STATE(name, interval_init, burst_init) \
@@ -28,12 +31,11 @@ struct ratelimit_state {
static inline void ratelimit_state_init(struct ratelimit_state *rs,
int interval, int burst)
{
+ memset(rs, 0, sizeof(*rs));
+
raw_spin_lock_init(&rs->lock);
rs->interval = interval;
rs->burst = burst;
- rs->printed = 0;
- rs->missed = 0;
- rs->begin = 0;
}

extern struct ratelimit_state printk_ratelimit_state;
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 5b5fdd8eeb75..18cfa5f5b058 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -450,6 +450,7 @@ struct devkmsg_user {
u64 seq;
u32 idx;
enum log_flags prev;
+ struct ratelimit_state rs;
struct mutex lock;
char buf[8192];
};
@@ -461,11 +462,15 @@ static ssize_t devkmsg_writev(struct kiocb *iocb, const struct iovec *iv,
int i;
int level = default_message_loglevel;
int facility = 1; /* LOG_USER */
+ struct file *file = iocb->ki_filp;
+ struct devkmsg_user *user = file->private_data;
size_t len = iov_length(iv, count);
ssize_t ret = len;

- if (len > LOG_LINE_MAX)
+ if (!user || len > LOG_LINE_MAX)
return -EINVAL;
+ if (!___ratelimit(&user->rs, current->comm))
+ return ret;
buf = kmalloc(len+1, GFP_KERNEL);
if (buf == NULL)
return -ENOMEM;
@@ -696,21 +701,25 @@ static unsigned int devkmsg_poll(struct file *file, poll_table *wait)
static int devkmsg_open(struct inode *inode, struct file *file)
{
struct devkmsg_user *user;
- int err;
-
- /* write-only does not need any file context */
- if ((file->f_flags & O_ACCMODE) == O_WRONLY)
- return 0;

- err = check_syslog_permissions(SYSLOG_ACTION_READ_ALL,
- SYSLOG_FROM_READER);
- if (err)
- return err;
+ /* write-only does not need to check read permissions */
+ if ((file->f_flags & O_ACCMODE) != O_WRONLY) {
+ int err = check_syslog_permissions(SYSLOG_ACTION_READ_ALL,
+ SYSLOG_FROM_READER);
+ if (err)
+ return err;
+ }

user = kmalloc(sizeof(struct devkmsg_user), GFP_KERNEL);
if (!user)
return -ENOMEM;

+ /* Configurable? */
+ ratelimit_state_init(&user->rs, DEFAULT_RATELIMIT_INTERVAL, DEFAULT_RATELIMIT_BURST);
+
+ /* We'll say something at release time. */
+ user->rs.flags |= RATELIMIT_MSG_ON_RELEASE;
+
mutex_init(&user->lock);

raw_spin_lock_irq(&logbuf_lock);
@@ -729,6 +738,10 @@ static int devkmsg_release(struct inode *inode, struct file *file)
if (!user)
return 0;

+ if (user->rs.missed)
+ pr_warning("%s: %d callbacks suppressed\n",
+ current->comm, user->rs.missed);
+
mutex_destroy(&user->lock);
kfree(user);
return 0;
diff --git a/lib/ratelimit.c b/lib/ratelimit.c
index 40e03ea2a967..97b461a9fd52 100644
--- a/lib/ratelimit.c
+++ b/lib/ratelimit.c
@@ -46,12 +46,13 @@ int ___ratelimit(struct ratelimit_state *rs, const char *func)
rs->begin = jiffies;

if (time_is_before_jiffies(rs->begin + rs->interval)) {
- if (rs->missed)
+ if (rs->missed && !(rs->flags & RATELIMIT_MSG_ON_RELEASE))
printk(KERN_WARNING "%s: %d callbacks suppressed\n",
func, rs->missed);
rs->begin = 0;
rs->printed = 0;
- rs->missed = 0;
+ if (!(rs->flags & RATELIMIT_MSG_ON_RELEASE))
+ rs->missed = 0;
}
if (rs->burst && rs->burst > rs->printed) {
rs->printed++;

--
Regards/Gruss,
Boris.

Sent from a fat crate under my desk. Formatting is fine.
--