linux-stable.git/kernel, branch v3.16.82

hrtimer: Get rid of the resolution field in hrtimer_clock_base

2020-02-11T20:03:54+00:00

commit 398ca17fb54b212cdc9da7ff4a17a35c48dd2103 upstream.

The field has no value because all clock bases have the same
resolution. The resolution only changes when we switch to high
resolution timer mode. We can evaluate that from a single static
variable as well. In the !HIGHRES case its simply a constant.

Export the variable, so we can simplify the usage sites.

Signed-off-by: Thomas Gleixner 
Reviewed-by: Preeti U Murthy 
Acked-by: Peter Zijlstra 
Cc: Viresh Kumar 
Cc: Marcelo Tosatti 
Cc: Frederic Weisbecker 
Link: http://lkml.kernel.org/r/20150414203500.645454122@linutronix.de
Signed-off-by: Thomas Gleixner 
[bwh: Backported to 3.16 as dependency of commit 552263456215
 "powerpc: Fix vDSO clock_getres()":
 - Adjust filename, context]
Signed-off-by: Ben Hutchings

futex: Prevent robust futex exit race

2020-02-11T20:03:41+00:00

commit ca16d5bee59807bf04deaab0a8eccecd5061528c upstream.

Robust futexes utilize the robust_list mechanism to allow the kernel to
release futexes which are held when a task exits. The exit can be voluntary
or caused by a signal or fault. This prevents that waiters block forever.

The futex operations in user space store a pointer to the futex they are
either locking or unlocking in the op_pending member of the per task robust
list.

After a lock operation has succeeded the futex is queued in the robust list
linked list and the op_pending pointer is cleared.

After an unlock operation has succeeded the futex is removed from the
robust list linked list and the op_pending pointer is cleared.

The robust list exit code checks for the pending operation and any futex
which is queued in the linked list. It carefully checks whether the futex
value is the TID of the exiting task. If so, it sets the OWNER_DIED bit and
tries to wake up a potential waiter.

This is race free for the lock operation but unlock has two race scenarios
where waiters might not be woken up. These issues can be observed with
regular robust pthread mutexes. PI aware pthread mutexes are not affected.

(1) Unlocking task is killed after unlocking the futex value in user space
    before being able to wake a waiter.

        pthread_mutex_unlock()
                |
                V
        atomic_exchange_rel (&mutex->__data.__lock, 0)
                        <------------------------killed
            lll_futex_wake ()                   |
                                                |
                                                |(__lock = 0)
                                                |(enter kernel)
                                                |
                                                V
                                            do_exit()
                                            exit_mm()
                                          mm_release()
                                        exit_robust_list()
                                        handle_futex_death()
                                                |
                                                |(__lock = 0)
                                                |(uval = 0)
                                                |
                                                V
        if ((uval & FUTEX_TID_MASK) != task_pid_vnr(curr))
                return 0;

    The sanity check which ensures that the user space futex is owned by
    the exiting task prevents the wakeup of waiters which in consequence
    block infinitely.

(2) Waiting task is killed after a wakeup and before it can acquire the
    futex in user space.

        OWNER                         WAITER
				futex_wait()
   pthread_mutex_unlock()               |
                |                       |
                |(__lock = 0)           |
                |                       |
                V                       |
         futex_wake() ------------>  wakeup()
                                        |
                                        |(return to userspace)
                                        |(__lock = 0)
                                        |
                                        V
                        oldval = mutex->__data.__lock
                                          <-----------------killed
    atomic_compare_and_exchange_val_acq (&mutex->__data.__lock,  |
                        id | assume_other_futex_waiters, 0)      |
                                                                 |
                                                                 |
                                                   (enter kernel)|
                                                                 |
                                                                 V
                                                         do_exit()
                                                        |
                                                        |
                                                        V
                                        handle_futex_death()
                                        |
                                        |(__lock = 0)
                                        |(uval = 0)
                                        |
                                        V
        if ((uval & FUTEX_TID_MASK) != task_pid_vnr(curr))
                return 0;

    The sanity check which ensures that the user space futex is owned
    by the exiting task prevents the wakeup of waiters, which seems to
    be correct as the exiting task does not own the futex value, but
    the consequence is that other waiters wont be woken up and block
    infinitely.

In both scenarios the following conditions are true:

   - task->robust_list->list_op_pending != NULL
   - user space futex value == 0
   - Regular futex (not PI)

If these conditions are met then it is reasonably safe to wake up a
potential waiter in order to prevent the above problems.

As this might be a false positive it can cause spurious wakeups, but the
waiter side has to handle other types of unrelated wakeups, e.g. signals
gracefully anyway. So such a spurious wakeup will not affect the
correctness of these operations.

This workaround must not touch the user space futex value and cannot set
the OWNER_DIED bit because the lock value is 0, i.e. uncontended. Setting
OWNER_DIED in this case would result in inconsistent state and subsequently
in malfunction of the owner died handling in user space.

The rest of the user space state is still consistent as no other task can
observe the list_op_pending entry in the exiting tasks robust list.

The eventually woken up waiter will observe the uncontended lock value and
take it over.

[ tglx: Massaged changelog and comment. Made the return explicit and not
  	depend on the subsequent check and added constants to hand into
  	handle_futex_death() instead of plain numbers. Fixed a few coding
	style issues. ]

Fixes: 0771dfefc9e5 ("[PATCH] lightweight robust futexes: core")
Signed-off-by: Yang Tao 
Signed-off-by: Yi Wang 
Signed-off-by: Thomas Gleixner 
Reviewed-by: Ingo Molnar 
Acked-by: Peter Zijlstra (Intel) 
Link: https://lkml.kernel.org/r/1573010582-35297-1-git-send-email-wang.yi59@zte.com.cn
Link: https://lkml.kernel.org/r/20191106224555.943191378@linutronix.de
[bwh: Backported to 3.16: Implementation is split between futex.c and
 futex_compat.c, with common definitions in ]
Signed-off-by: Ben Hutchings

workqueue: Fix spurious sanity check failures in destroy_workqueue()

2020-02-11T20:03:11+00:00

commit def98c84b6cdf2eeea19ec5736e90e316df5206b upstream.

Before actually destrying a workqueue, destroy_workqueue() checks
whether it's actually idle.  If it isn't, it prints out a bunch of
warning messages and leaves the workqueue dangling.  It unfortunately
has a couple issues.

* Mayday list queueing increments pwq's refcnts which gets detected as
  busy and fails the sanity checks.  However, because mayday list
  queueing is asynchronous, this condition can happen without any
  actual work items left in the workqueue.

* Sanity check failure leaves the sysfs interface behind too which can
  lead to init failure of newer instances of the workqueue.

This patch fixes the above two by

* If a workqueue has a rescuer, disable and kill the rescuer before
  sanity checks.  Disabling and killing is guaranteed to flush the
  existing mayday list.

* Remove sysfs interface before sanity checks.

Signed-off-by: Tejun Heo 
Reported-by: Marcin Pawlowski 
Reported-by: "Williams, Gerald S" 
[bwh: Backported to 3.16: destroy_workqueue() also freed wq->rescuer itself]
Signed-off-by: Ben Hutchings

Revert "sched/fair: Fix bandwidth timer clock drift condition"

2020-01-11T02:05:04+00:00

This reverts commit eb29ee5a3873134917a760bf9c416da0a089a0be, which
was commit 512ac999d2755d2b7109e996a76b6fb8b888631d upstream.  This
introduced a regression and doesn't seem to have been suitable for
older stable branches.  (It has been fixed differently upstream.)

Signed-off-by: Ben Hutchings

PM / Hibernate: Call flush_icache_range() on pages restored in-place

2020-01-11T02:04:55+00:00

commit f6cf0545ec697ddc278b7457b7d0c0d86a2ea88e upstream.

Some architectures require code written to memory as if it were data to be
'cleaned' from any data caches before the processor can fetch them as new
instructions.

During resume from hibernate, the snapshot code copies some pages directly,
meaning these architectures do not get a chance to perform their cache
maintenance. Modify the read and decompress code to call
flush_icache_range() on all pages that are restored, so that the restored
in-place pages are guaranteed to be executable on these architectures.

Signed-off-by: James Morse 
Acked-by: Pavel Machek 
Acked-by: Rafael J. Wysocki 
Acked-by: Catalin Marinas 
[will: make clean_pages_on_* static and remove initialisers]
Signed-off-by: Will Deacon 
Cc: Arnd Bergmann 
Signed-off-by: Ben Hutchings

suspend: simplify block I/O handling

2020-01-11T02:04:54+00:00

commit 343df3c79c62b644ce6ff5dff96c9e0be1ecb242 upstream.

Stop abusing struct page functionality and the swap end_io handler, and
instead add a modified version of the blk-lib.c bio_batch helpers.

Also move the block I/O code into swap.c as they are directly tied into
each other.

Signed-off-by: Christoph Hellwig 
Tested-by: Pavel Machek 
Tested-by: Ming Lin 
Acked-by: Pavel Machek 
Acked-by: Rafael J. Wysocki 
Signed-off-by: Jens Axboe 
[bwh: Backported to 3.16 as dependency of commit f6cf0545ec69
 "PM / Hibernate: Call flush_icache_range() on pages restored in-place":
 - Adjust context]
Signed-off-by: Ben Hutchings

tracing/uprobes: Fix output for multiple string arguments

2020-01-11T02:04:41+00:00

commit 0722069a5374b904ec1a67f91249f90e1cfae259 upstream.

When printing multiple uprobe arguments as strings the output for the
earlier arguments would also include all later string arguments.

This is best explained in an example:

Consider adding a uprobe to a function receiving two strings as
parameters which is at offset 0xa0 in strlib.so and we want to print
both parameters when the uprobe is hit (on x86_64):

$ echo 'p:func /lib/strlib.so:0xa0 +0(%di):string +0(%si):string' > \
    /sys/kernel/debug/tracing/uprobe_events

When the function is called as func("foo", "bar") and we hit the probe,
the trace file shows a line like the following:

  [...] func: (0x7f7e683706a0) arg1="foobar" arg2="bar"

Note the extra "bar" printed as part of arg1. This behaviour stacks up
for additional string arguments.

The strings are stored in a dynamically growing part of the uprobe
buffer by fetch_store_string() after copying them from userspace via
strncpy_from_user(). The return value of strncpy_from_user() is then
directly used as the required size for the string. However, this does
not take the terminating null byte into account as the documentation
for strncpy_from_user() cleary states that it "[...] returns the
length of the string (not including the trailing NUL)" even though the
null byte will be copied to the destination.

Therefore, subsequent calls to fetch_store_string() will overwrite
the terminating null byte of the most recently fetched string with
the first character of the current string, leading to the
"accumulation" of strings in earlier arguments in the output.

Fix this by incrementing the return value of strncpy_from_user() by
one if we did not hit the maximum buffer size.

Link: http://lkml.kernel.org/r/20190116141629.5752-1-andreas.ziegler@fau.de

Cc: Ingo Molnar 
Fixes: 5baaa59ef09e ("tracing/probes: Implement 'memory' fetch method for uprobes")
Acked-by: Masami Hiramatsu 
Signed-off-by: Andreas Ziegler 
Signed-off-by: Steven Rostedt (VMware) 
Signed-off-by: Masami Hiramatsu 
Signed-off-by: Ben Hutchings

tracing: Get trace_array reference for available_tracers files

2019-12-19T15:58:27+00:00

commit 194c2c74f5532e62c218adeb8e2b683119503907 upstream.

As instances may have different tracers available, we need to look at the
trace_array descriptor that shows the list of the available tracers for the
instance. But there's a race between opening the file and an admin
deleting the instance. The trace_array_get() needs to be called before
accessing the trace_array.

Fixes: 607e2ea167e56 ("tracing: Set up infrastructure to allow tracers for instances")
Signed-off-by: Steven Rostedt (VMware) 
Signed-off-by: Ben Hutchings

sched/fair: Scale bandwidth quota and period without losing quota/period ratio precision

2019-12-19T15:58:17+00:00

commit 4929a4e6faa0f13289a67cae98139e727f0d4a97 upstream.

The quota/period ratio is used to ensure a child task group won't get
more bandwidth than the parent task group, and is calculated as:

  normalized_cfs_quota() = [(quota_us << 20) / period_us]

If the quota/period ratio was changed during this scaling due to
precision loss, it will cause inconsistency between parent and child
task groups.

See below example:

A userspace container manager (kubelet) does three operations:

 1) Create a parent cgroup, set quota to 1,000us and period to 10,000us.
 2) Create a few children cgroups.
 3) Set quota to 1,000us and period to 10,000us on a child cgroup.

These operations are expected to succeed. However, if the scaling of
147/128 happens before step 3, quota and period of the parent cgroup
will be changed:

  new_quota: 1148437ns,   1148us
 new_period: 11484375ns, 11484us

And when step 3 comes in, the ratio of the child cgroup will be
104857, which will be larger than the parent cgroup ratio (104821),
and will fail.

Scaling them by a factor of 2 will fix the problem.

Tested-by: Phil Auld 
Signed-off-by: Xuewei Zhang 
Signed-off-by: Peter Zijlstra (Intel) 
Acked-by: Phil Auld 
Cc: Anton Blanchard 
Cc: Ben Segall 
Cc: Dietmar Eggemann 
Cc: Juri Lelli 
Cc: Linus Torvalds 
Cc: Mel Gorman 
Cc: Peter Zijlstra 
Cc: Steven Rostedt 
Cc: Thomas Gleixner 
Cc: Vincent Guittot 
Fixes: 2e8e19226398 ("sched/fair: Limit sched_cfs_period_timer() loop to avoid hard lockup")
Link: https://lkml.kernel.org/r/20191004001243.140897-1-xueweiz@google.com
Signed-off-by: Ingo Molnar 
Signed-off-by: Ben Hutchings

panic: ensure preemption is disabled during panic()

2019-12-19T15:58:13+00:00

commit 20bb759a66be52cf4a9ddd17fddaf509e11490cd upstream.

Calling 'panic()' on a kernel with CONFIG_PREEMPT=y can leave the
calling CPU in an infinite loop, but with interrupts and preemption
enabled.  From this state, userspace can continue to be scheduled,
despite the system being "dead" as far as the kernel is concerned.

This is easily reproducible on arm64 when booting with "nosmp" on the
command line; a couple of shell scripts print out a periodic "Ping"
message whilst another triggers a crash by writing to
/proc/sysrq-trigger:

  | sysrq: Trigger a crash
  | Kernel panic - not syncing: sysrq triggered crash
  | CPU: 0 PID: 1 Comm: init Not tainted 5.2.15 #1
  | Hardware name: linux,dummy-virt (DT)
  | Call trace:
  |  dump_backtrace+0x0/0x148
  |  show_stack+0x14/0x20
  |  dump_stack+0xa0/0xc4
  |  panic+0x140/0x32c
  |  sysrq_handle_reboot+0x0/0x20
  |  __handle_sysrq+0x124/0x190
  |  write_sysrq_trigger+0x64/0x88
  |  proc_reg_write+0x60/0xa8
  |  __vfs_write+0x18/0x40
  |  vfs_write+0xa4/0x1b8
  |  ksys_write+0x64/0xf0
  |  __arm64_sys_write+0x14/0x20
  |  el0_svc_common.constprop.0+0xb0/0x168
  |  el0_svc_handler+0x28/0x78
  |  el0_svc+0x8/0xc
  | Kernel Offset: disabled
  | CPU features: 0x0002,24002004
  | Memory Limit: none
  | ---[ end Kernel panic - not syncing: sysrq triggered crash ]---
  |  Ping 2!
  |  Ping 1!
  |  Ping 1!
  |  Ping 2!

The issue can also be triggered on x86 kernels if CONFIG_SMP=n,
otherwise local interrupts are disabled in 'smp_send_stop()'.

Disable preemption in 'panic()' before re-enabling interrupts.

Link: http://lkml.kernel.org/r/20191002123538.22609-1-will@kernel.org
Link: https://lore.kernel.org/r/BX1W47JXPMR8.58IYW53H6M5N@dragonstone
Signed-off-by: Will Deacon 
Reported-by: Xogium 
Reviewed-by: Kees Cook 
Cc: Russell King 
Cc: Greg Kroah-Hartman 
Cc: Ingo Molnar 
Cc: Petr Mladek 
Cc: Feng Tang 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds 
Signed-off-by: Ben Hutchings