linux-toradex.git/kernel, branch v3.2.64

ring-buffer: Fix infinite spin in reading buffer

2014-11-05T20:27:49+00:00

commit 24607f114fd14f2f37e3e0cb3d47bce96e81e848 upstream.

Commit 651e22f2701b "ring-buffer: Always reset iterator to reader page"
fixed one bug but in the process caused another one. The reset is to
update the header page, but that fix also changed the way the cached
reads were updated. The cache reads are used to test if an iterator
needs to be updated or not.

A ring buffer iterator, when created, disables writes to the ring buffer
but does not stop other readers or consuming reads from happening.
Although all readers are synchronized via a lock, they are only
synchronized when in the ring buffer functions. Those functions may
be called by any number of readers. The iterator continues down when
its not interrupted by a consuming reader. If a consuming read
occurs, the iterator starts from the beginning of the buffer.

The way the iterator sees that a consuming read has happened since
its last read is by checking the reader "cache". The cache holds the
last counts of the read and the reader page itself.

Commit 651e22f2701b changed what was saved by the cache_read when
the rb_iter_reset() occurred, making the iterator never match the cache.
Then if the iterator calls rb_iter_reset(), it will go into an
infinite loop by checking if the cache doesn't match, doing the reset
and retrying, just to see that the cache still doesn't match! Which
should never happen as the reset is suppose to set the cache to the
current value and there's locks that keep a consuming reader from
having access to the data.

Fixes: 651e22f2701b "ring-buffer: Always reset iterator to reader page"
Signed-off-by: Steven Rostedt 
Signed-off-by: Ben Hutchings

perf: fix perf bug in fork()

2014-11-05T20:27:46+00:00

commit 6c72e3501d0d62fc064d3680e5234f3463ec5a86 upstream.

Oleg noticed that a cleanup by Sylvain actually uncovered a bug; by
calling perf_event_free_task() when failing sched_fork() we will not yet
have done the memset() on ->perf_event_ctxp[] and will therefore try and
'free' the inherited contexts, which are still in use by the parent
process.  This is bad..

Suggested-by: Oleg Nesterov 
Reported-by: Oleg Nesterov 
Reported-by: Sylvain 'ythier' Hitier 
Signed-off-by: Peter Zijlstra (Intel) 
Cc: Ingo Molnar 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds 
Signed-off-by: Ben Hutchings

alarmtimer: Lock k_itimer during timer callback

2014-11-05T20:27:43+00:00

commit 474e941bed9262f5fa2394f9a4a67e24499e5926 upstream.

Locks the k_itimer's it_lock member when handling the alarm timer's
expiry callback.

The regular posix timers defined in posix-timers.c have this lock held
during timout processing because their callbacks are routed through
posix_timer_fn().  The alarm timers follow a different path, so they
ought to grab the lock somewhere else.

Cc: Thomas Gleixner 
Cc: Ingo Molnar 
Cc: Richard Cochran 
Cc: Prarit Bhargava 
Cc: Sharvil Nanavati 
Signed-off-by: Richard Larocque 
Signed-off-by: John Stultz 
Signed-off-by: Ben Hutchings

alarmtimer: Do not signal SIGEV_NONE timers

2014-11-05T20:27:43+00:00

commit 265b81d23a46c39df0a735a3af4238954b41a4c2 upstream.

Avoids sending a signal to alarm timers created with sigev_notify set to
SIGEV_NONE by checking for that special case in the timeout callback.

The regular posix timers avoid sending signals to SIGEV_NONE timers by
not scheduling any callbacks for them in the first place.  Although it
would be possible to do something similar for alarm timers, it's simpler
to handle this as a special case in the timeout.

Prior to this patch, the alarm timer would ignore the sigev_notify value
and try to deliver signals to the process anyway.  Even worse, the
sanity check for the value of sigev_signo is skipped when SIGEV_NONE was
specified, so the signal number could be bogus.  If sigev_signo was an
unitialized value (as it often would be if SIGEV_NONE is used), then
it's hard to predict which signal will be sent.

Cc: Thomas Gleixner 
Cc: Ingo Molnar 
Cc: Richard Cochran 
Cc: Prarit Bhargava 
Cc: Sharvil Nanavati 
Signed-off-by: Richard Larocque 
Signed-off-by: John Stultz 
Signed-off-by: Ben Hutchings

alarmtimer: Return relative times in timer_gettime

2014-11-05T20:27:43+00:00

commit e86fea764991e00a03ff1e56409ec9cacdbda4c9 upstream.

Returns the time remaining for an alarm timer, rather than the time at
which it is scheduled to expire.  If the timer has already expired or it
is not currently scheduled, the it_value's members are set to zero.

This new behavior matches that of the other posix-timers and the POSIX
specifications.

This is a change in user-visible behavior, and may break existing
applications.  Hopefully, few users rely on the old incorrect behavior.

Cc: Thomas Gleixner 
Cc: Ingo Molnar 
Cc: Richard Cochran 
Cc: Prarit Bhargava 
Cc: Sharvil Nanavati 
Signed-off-by: Richard Larocque 
[jstultz: minor style tweak]
Signed-off-by: John Stultz 
[bwh: Backported to 3.2: Add definition of alarm_expires_remaining() from
 commit 6cffe00f7d4e ('alarmtimer: Add functions for timerfd support')]
Signed-off-by: Ben Hutchings

jiffies: Fix timeval conversion to jiffies

2014-11-05T20:27:43+00:00

commit d78c9300c51d6ceed9f6d078d4e9366f259de28c upstream.

timeval_to_jiffies tried to round a timeval up to an integral number
of jiffies, but the logic for doing so was incorrect: intervals
corresponding to exactly N jiffies would become N+1. This manifested
itself particularly repeatedly stopping/starting an itimer:

setitimer(ITIMER_PROF, &val, NULL);
setitimer(ITIMER_PROF, NULL, &val);

would add a full tick to val, _even if it was exactly representable in
terms of jiffies_ (say, the result of a previous rounding.)  Doing
this repeatedly would cause unbounded growth in val.  So fix the math.

Here's what was wrong with the conversion: we essentially computed
(eliding seconds)

jiffies = usec  * (NSEC_PER_USEC/TICK_NSEC)

by using scaling arithmetic, which took the best approximation of
NSEC_PER_USEC/TICK_NSEC with denominator of 2^USEC_JIFFIE_SC =
x/(2^USEC_JIFFIE_SC), and computed:

jiffies = (usec * x) >> USEC_JIFFIE_SC

and rounded this calculation up in the intermediate form (since we
can't necessarily exactly represent TICK_NSEC in usec.) But the
scaling arithmetic is a (very slight) *over*approximation of the true
value; that is, instead of dividing by (1 usec/ 1 jiffie), we
effectively divided by (1 usec/1 jiffie)-epsilon (rounding
down). This would normally be fine, but we want to round timeouts up,
and we did so by adding 2^USEC_JIFFIE_SC - 1 before the shift; this
would be fine if our division was exact, but dividing this by the
slightly smaller factor was equivalent to adding just _over_ 1 to the
final result (instead of just _under_ 1, as desired.)

In particular, with HZ=1000, we consistently computed that 10000 usec
was 11 jiffies; the same was true for any exact multiple of
TICK_NSEC.

We could possibly still round in the intermediate form, adding
something less than 2^USEC_JIFFIE_SC - 1, but easier still is to
convert usec->nsec, round in nanoseconds, and then convert using
time*spec*_to_jiffies.  This adds one constant multiplication, and is
not observably slower in microbenchmarks on recent x86 hardware.

Tested: the following program:

int main() {
  struct itimerval zero = {{0, 0}, {0, 0}};
  /* Initially set to 10 ms. */
  struct itimerval initial = zero;
  initial.it_interval.tv_usec = 10000;
  setitimer(ITIMER_PROF, &initial, NULL);
  /* Save and restore several times. */
  for (size_t i = 0; i < 10; ++i) {
    struct itimerval prev;
    setitimer(ITIMER_PROF, &zero, &prev);
    /* on old kernels, this goes up by TICK_USEC every iteration */
    printf("previous value: %ld %ld %ld %ld\n",
           prev.it_interval.tv_sec, prev.it_interval.tv_usec,
           prev.it_value.tv_sec, prev.it_value.tv_usec);
    setitimer(ITIMER_PROF, &prev, NULL);
  }
    return 0;
}

Cc: Thomas Gleixner 
Cc: Ingo Molnar 
Cc: Paul Turner 
Cc: Richard Cochran 
Cc: Prarit Bhargava 
Reviewed-by: Paul Turner 
Reported-by: Aaron Jacobs 
Signed-off-by: Andrew Hunter 
[jstultz: Tweaked to apply to 3.17-rc]
Signed-off-by: John Stultz 
[bwh: Backported to 3.2: adjust filename]
Signed-off-by: Ben Hutchings

futex: Unlock hb->lock in futex_wait_requeue_pi() error path

2014-11-05T20:27:43+00:00

commit 13c42c2f43b19aab3195f2d357db00d1e885eaa8 upstream.

futex_wait_requeue_pi() calls futex_wait_setup(). If
futex_wait_setup() succeeds it returns with hb->lock held and
preemption disabled. Now the sanity check after this does:

        if (match_futex(&q.key, &key2)) {
	   	ret = -EINVAL;
		goto out_put_keys;
	}

which releases the keys but does not release hb->lock.

So we happily return to user space with hb->lock held and therefor
preemption disabled.

Unlock hb->lock before taking the exit route.

Reported-by: Dave "Trinity" Jones 
Signed-off-by: Thomas Gleixner 
Reviewed-by: Darren Hart 
Reviewed-by: Davidlohr Bueso 
Cc: Peter Zijlstra 
Link: http://lkml.kernel.org/r/alpine.DEB.2.10.1409112318500.4178@nanos
Signed-off-by: Thomas Gleixner 
[bwh: Backported to 3.2: queue_unlock() takes two parameters]
Signed-off-by: Ben Hutchings

perf: Fix a race condition in perf_remove_from_context()

2014-11-05T20:27:41+00:00

commit 3577af70a2ce4853d58e57d832e687d739281479 upstream.

We saw a kernel soft lockup in perf_remove_from_context(),
it looks like the `perf` process, when exiting, could not go
out of the retry loop. Meanwhile, the target process was forking
a child. So either the target process should execute the smp
function call to deactive the event (if it was running) or it should
do a context switch which deactives the event.

It seems we optimize out a context switch in perf_event_context_sched_out(),
and what's more important, we still test an obsolete task pointer when
retrying, so no one actually would deactive that event in this situation.
Fix it directly by reloading the task pointer in perf_remove_from_context().

This should cure the above soft lockup.

Signed-off-by: Cong Wang 
Signed-off-by: Cong Wang 
Signed-off-by: Peter Zijlstra 
Cc: Paul Mackerras 
Cc: Arnaldo Carvalho de Melo 
Cc: Linus Torvalds 
Link: http://lkml.kernel.org/r/1409696840-843-1-git-send-email-xiyou.wangcong@gmail.com
Signed-off-by: Ingo Molnar 
Signed-off-by: Ben Hutchings

cgroup: reject cgroup names with '

2014-11-05T20:27:39+00:00

'

commit 71b1fb5c4473a5b1e601d41b109bdfe001ec82e0 upstream.

/proc//cgroup contains one cgroup path on each line. If cgroup names are
allowed to contain "\n", applications cannot parse /proc//cgroup safely.

Signed-off-by: Alban Crequy 
Signed-off-by: Tejun Heo 
[bwh: Backported to 3.2:
 - Adjust context
 - We have to get the name from the dentry pointer]
Signed-off-by: Ben Hutchings

ring-buffer: Always reset iterator to reader page

2014-09-13T22:41:44+00:00

commit 651e22f2701b4113989237c3048d17337dd2185c upstream.

When performing a consuming read, the ring buffer swaps out a
page from the ring buffer with a empty page and this page that
was swapped out becomes the new reader page. The reader page
is owned by the reader and since it was swapped out of the ring
buffer, writers do not have access to it (there's an exception
to that rule, but it's out of scope for this commit).

When reading the "trace" file, it is a non consuming read, which
means that the data in the ring buffer will not be modified.
When the trace file is opened, a ring buffer iterator is allocated
and writes to the ring buffer are disabled, such that the iterator
will not have issues iterating over the data.

Although the ring buffer disabled writes, it does not disable other
reads, or even consuming reads. If a consuming read happens, then
the iterator is reset and starts reading from the beginning again.

My tests would sometimes trigger this bug on my i386 box:

WARNING: CPU: 0 PID: 5175 at kernel/trace/trace.c:1527 __trace_find_cmdline+0x66/0xaa()
Modules linked in:
CPU: 0 PID: 5175 Comm: grep Not tainted 3.16.0-rc3-test+ #8
Hardware name:                  /DG965MQ, BIOS MQ96510J.86A.0372.2006.0605.1717 06/05/2006
 00000000 00000000 f09c9e1c c18796b3 c1b5d74c f09c9e4c c103a0e3 c1b5154b
 f09c9e78 00001437 c1b5d74c 000005f7 c10bd85a c10bd85a c1cac57c f09c9eb0
 ed0e0000 f09c9e64 c103a185 00000009 f09c9e5c c1b5154b f09c9e78 f09c9e80^M
Call Trace:
 [] dump_stack+0x4b/0x75
 [] warn_slowpath_common+0x7e/0x95
 [] ? __trace_find_cmdline+0x66/0xaa
 [] ? __trace_find_cmdline+0x66/0xaa
 [] warn_slowpath_fmt+0x33/0x35
 [] __trace_find_cmdline+0x66/0xaa^M
 [] trace_find_cmdline+0x40/0x64
 [] trace_print_context+0x27/0xec
 [] ? trace_seq_printf+0x37/0x5b
 [] print_trace_line+0x319/0x39b
 [] ? ring_buffer_read+0x47/0x50
 [] s_show+0x192/0x1ab
 [] ? s_next+0x5a/0x7c
 [] seq_read+0x267/0x34c
 [] vfs_read+0x8c/0xef
 [] ? seq_lseek+0x154/0x154
 [] SyS_read+0x54/0x7f
 [] syscall_call+0x7/0xb
---[ end trace 3f507febd6b4cc83 ]---
>>>> ##### CPU 1 buffer started ####

Which was the __trace_find_cmdline() function complaining about the pid
in the event record being negative.

After adding more test cases, this would trigger more often. Strangely
enough, it would never trigger on a single test, but instead would trigger
only when running all the tests. I believe that was the case because it
required one of the tests to be shutting down via delayed instances while
a new test started up.

After spending several days debugging this, I found that it was caused by
the iterator becoming corrupted. Debugging further, I found out why
the iterator became corrupted. It happened with the rb_iter_reset().

As consuming reads may not read the full reader page, and only part
of it, there's a "read" field to know where the last read took place.
The iterator, must also start at the read position. In the rb_iter_reset()
code, if the reader page was disconnected from the ring buffer, the iterator
would start at the head page within the ring buffer (where writes still
happen). But the mistake there was that it still used the "read" field
to start the iterator on the head page, where it should always start
at zero because readers never read from within the ring buffer where
writes occur.

I originally wrote a patch to have it set the iter->head to 0 instead
of iter->head_page->read, but then I questioned why it wasn't always
setting the iter to point to the reader page, as the reader page is
still valid.  The list_empty(reader_page->list) just means that it was
successful in swapping out. But the reader_page may still have data.

There was a bug report a long time ago that was not reproducible that
had something about trace_pipe (consuming read) not matching trace
(iterator read). This may explain why that happened.

Anyway, the correct answer to this bug is to always use the reader page
an not reset the iterator to inside the writable ring buffer.

Fixes: d769041f8653 "ring_buffer: implement new locking"
Signed-off-by: Steven Rostedt 
Signed-off-by: Ben Hutchings