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  1. 20 Dec, 2023 6 commits
  3. 19 Dec, 2023 6 commits
    • Kent Overstreet's avatar
      bcachefs; guard against overflow in btree node split · 7ba1f6ec
      Kent Overstreet authored 
      Signed-off-by: default avatarKent Overstreet <kent.overstreet@linux.dev>
      7ba1f6ec
    • Kent Overstreet's avatar
      bcachefs: btree_node_u64s_with_format() takes nr keys · 0fa3b977
      Kent Overstreet authored 
      Signed-off-by: default avatarKent Overstreet <kent.overstreet@linux.dev>
      0fa3b977
    • Linus Torvalds's avatar
      Merge tag 'trace-v6.7-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace · 55cb5f43
      Linus Torvalds authored 
      Pull tracing fix from Steven Rostedt:
 "While working on the ring buffer, I found one more bug with the
  timestamp code, and the fix for this removed the need for the final
  64-bit cmpxchg!

  The ring buffer events hold a "delta" from the previous event. If it
  is determined that the delta can not be calculated, it falls back to
  adding an absolute timestamp value. The way to know if the delta can
  be used is via two stored timestamps in the per-cpu buffer meta data:

   before_stamp and write_stamp

  The before_stamp is written by every event before it tries to allocate
  its space on the ring buffer. The write_stamp is written after it
  allocates its space and knows that nothing came in after it read the
  previous before_stamp and write_stamp and the two matched.

  A previous fix dd939425 ("ring-buffer: Do not try to put back
  write_stamp") removed putting back the write_stamp to match the
  before_stamp so that the next event could use the delta, but races
  were found where the two would match, but not be for of the previous
  event.

  It was determined to allow the event reservation to not have a valid
  write_stamp when it is finished, and this fixed a lot of races.

  The last use of the 64-bit timestamp cmpxchg depended on the
  write_stamp being valid after an interruption. But this is no longer
  the case, as if an event is interrupted by a softirq that writes an
  event, and that event gets interrupted by a hardirq or NMI and that
  writes an event, then the softirq could finish its reservation without
  a valid write_stamp.

  In the slow path of the event reservation, a delta can still be used
  if the write_stamp is valid. Instead of using a cmpxchg against the
  write stamp, the before_stamp needs to be read again to validate the
  write_stamp. The cmpxchg is not needed.

  This updates the slowpath to validate the write_stamp by comparing it
  to the before_stamp and removes all rb_time_cmpxchg() as there are no
  more users of that function.

  The removal of the 32-bit updates of rb_time_t will be done in the
  next merge window"

* tag 'trace-v6.7-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
  ring-buffer: Fix slowpath of interrupted event
      55cb5f43
    • Linus Torvalds's avatar
      Merge tag 'arc-6.7-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/vgupta/arc · 9c749e61
      Linus Torvalds authored 
      Pull ARC fixes from Vineet Gupta:

 - build error for hugetlb, sparse and smatch fixes

 - removal of VIPT aliasing cache code

* tag 'arc-6.7-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/vgupta/arc:
  ARC: add hugetlb definitions
  ARC: fix smatch warning
  ARC: fix spare error
  ARC: mm: retire support for aliasing VIPT D$
  ARC: entry: move ARCompact specific bits out of entry.h
  ARC: entry: SAVE_ABI_CALLEE_REG: ISA/ABI specific helper
      9c749e61
    • Steven Rostedt (Google)'s avatar
      ring-buffer: Fix slowpath of interrupted event · b803d7c6
      Steven Rostedt (Google) authored 
      To synchronize the timestamps with the ring buffer reservation, there are
two timestamps that are saved in the buffer meta data.

1. before_stamp
2. write_stamp

When the two are equal, the write_stamp is considered valid, as in, it may
be used to calculate the delta of the next event as the write_stamp is the
timestamp of the previous reserved event on the buffer.

This is done by the following:

 /*A*/	w = current position on the ring buffer
	before = before_stamp
	after = write_stamp
	ts = read current timestamp

	if (before != after) {
		write_stamp is not valid, force adding an absolute
		timestamp.
	}

 /*B*/	before_stamp = ts

 /*C*/	write = local_add_return(event length, position on ring buffer)

	if (w == write - event length) {
		/* Nothing interrupted between A and C */
 /*E*/		write_stamp = ts;
		delta = ts - after
		/*
		 * If nothing interrupted again,
		 * before_stamp == write_stamp and write_stamp
		 * can be used to calculate the delta for
		 * events that come in after this one.
		 */
	} else {

		/*
		 * The slow path!
		 * Was interrupted between A and C.
		 */

This is the place that there's a bug. We currently have:

		after = write_stamp
		ts = read current timestamp

 /*F*/		if (write == current position on the ring buffer &&
		    after < ts && cmpxchg(write_stamp, after, ts)) {

			delta = ts - after;

		} else {
			delta = 0;
		}

The assumption is that if the current position on the ring buffer hasn't
moved between C and F, then it also was not interrupted, and that the last
event written has a timestamp that matches the write_stamp. That is the
write_stamp is valid.

But this may not be the case:

If a task context event was interrupted by softirq between B and C.

And the softirq wrote an event that got interrupted by a hard irq between
C and E.

and the hard irq wrote an event (does not need to be interrupted)

We have:

 /*B*/ before_stamp = ts of normal context

   ---> interrupted by softirq

	/*B*/ before_stamp = ts of softirq context

	  ---> interrupted by hardirq

		/*B*/ before_stamp = ts of hard irq context
		/*E*/ write_stamp = ts of hard irq context

		/* matches and write_stamp valid */
	  <----

	/*E*/ write_stamp = ts of softirq context

	/* No longer matches before_stamp, write_stamp is not valid! */

   <---

 w != write - length, go to slow path

// Right now the order of events in the ring buffer is:
//
// |-- softirq event --|-- hard irq event --|-- normal context event --|
//

 after = write_stamp (this is the ts of softirq)
 ts = read current timestamp

 if (write == current position on the ring buffer [true] &&
     after < ts [true] && cmpxchg(write_stamp, after, ts) [true]) {

	delta = ts - after  [Wrong!]

The delta is to be between the hard irq event and the normal context
event, but the above logic made the delta between the softirq event and
the normal context event, where the hard irq event is between the two. This
will shift all the remaining event timestamps on the sub-buffer
incorrectly.

The write_stamp is only valid if it matches the before_stamp. The cmpxchg
does nothing to help this.

Instead, the following logic can be done to fix this:

	before = before_stamp
	ts = read current timestamp
	before_stamp = ts

	after = write_stamp

	if (write == current position on the ring buffer &&
	    after == before && after < ts) {

		delta = ts - after

	} else {
		delta = 0;
	}

The above will only use the write_stamp if it still matches before_stamp
and was tested to not have changed since C.

As a bonus, with this logic we do not need any 64-bit cmpxchg() at all!

This means the 32-bit rb_time_t workaround can finally be removed. But
that's for a later time.

Link: https://lore.kernel.org/linux-trace-kernel/20231218175229.58ec3daf@gandalf.local.home/
Link: https://lore.kernel.org/linux-trace-kernel/20231218230712.3a76b081@gandalf.local.home

Cc: stable@vger.kernel.org
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Fixes: dd939425 ("ring-buffer: Do not try to put back write_stamp")
Signed-off-by: default avatarSteven Rostedt (Google) <rostedt@goodmis.org>
      b803d7c6
    • Linus Torvalds's avatar
      Merge tag 'hid-for-linus-2023121901' of git://git.kernel.org/pub/scm/linux/kernel/git/hid/hid · 3f10e214
      Linus Torvalds authored 
      Pull HID fixes from Jiri Kosina:

 - fix for division by zero in Nintendo driver when generic joycon is
   attached, reported and fixed by SteamOS folks (Guilherme G. Piccoli)

 - GCC-7 build fix (which is a good cleanup anyway) for Nintendo driver
   (Ryan McClelland)

* tag 'hid-for-linus-2023121901' of git://git.kernel.org/pub/scm/linux/kernel/git/hid/hid:
  HID: nintendo: Prevent divide-by-zero on code
  HID: nintendo: fix initializer element is not constant error
      3f10e214
  5. 18 Dec, 2023 18 commits
  7. 17 Dec, 2023 10 commits
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