ext4: fix data offset overflow in ext4_xattr_fiemap() on 32-bit archs

commit a60697f411eb365fb09e639e6f183fe33d1eb796 upstream.

On 32-bit architectures with 32-bit sector_t computation of data offset
in ext4_xattr_fiemap() can overflow resulting in reporting bogus data
location. Fix the problem by typing block number to proper type before
shifting.

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
ext4: fix overflow when counting used blocks on 32-bit architectures

commit 8af8eecc1331dbf5e8c662022272cf667e213da5 upstream.

The arithmetics adding delalloc blocks to the number of used blocks in
ext4_getattr() can easily overflow on 32-bit archs as we first multiply
number of blocks by blocksize and then divide back by 512. Make the
arithmetics more clever and also use proper type (unsigned long long
instead of unsigned long).

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
ext4: don't allow ext4_free_blocks() to fail due to ENOMEM

commit e7676a704ee0a1ef71a6b23760b5a8f6896cb1a1 upstream.

The filesystem should not be marked inconsistent if ext4_free_blocks()
is not able to allocate memory.  Unfortunately some callers (most
notably ext4_truncate) don't have a way to reflect an error back up to
the VFS.  And even if we did, most userspace applications won't deal
with most system calls returning ENOMEM anyway.

Reported-by: Nagachandra P <nagachandra@gmail.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
ARM: 7765/1: perf: Record the user-mode PC in the call chain.

commit c5f927a6f62196226915f12194c9d0df4e2210d7 upstream.

With this change, we no longer lose the innermost entry in the user-mode
part of the call chain.  See also the x86 port, which includes the ip.

It's possible to partially work around this problem by post-processing
the data to use the PERF_SAMPLE_IP value, but this works only if the CPU
wasn't in the kernel when the sample was taken.

Signed-off-by: Jed Davis <jld@mozilla.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
drivers/dma/pl330.c: fix locking in pl330_free_chan_resources()

commit da331ba8e9c5de72a27e50f71105395bba6eebe0 upstream.

tasklet_kill() may sleep so call it before taking pch->lock.

Fixes following lockup:

  BUG: scheduling while atomic: cat/2383/0x00000002
  Modules linked in:
    unwind_backtrace+0x0/0xfc
    __schedule_bug+0x4c/0x58
    __schedule+0x690/0x6e0
    sys_sched_yield+0x70/0x78
    tasklet_kill+0x34/0x8c
    pl330_free_chan_resources+0x24/0x88
    dma_chan_put+0x4c/0x50
  [...]
  BUG: spinlock lockup suspected on CPU#0, swapper/0/0
   lock: 0xe52aa04c, .magic: dead4ead, .owner: cat/2383, .owner_cpu: 1
    unwind_backtrace+0x0/0xfc
    do_raw_spin_lock+0x194/0x204
    _raw_spin_lock_irqsave+0x20/0x28
    pl330_tasklet+0x2c/0x5a8
    tasklet_action+0xfc/0x114
    __do_softirq+0xe4/0x19c
    irq_exit+0x98/0x9c
    handle_IPI+0x124/0x16c
    gic_handle_irq+0x64/0x68
    __irq_svc+0x40/0x70
    cpuidle_wrap_enter+0x4c/0xa0
    cpuidle_enter_state+0x18/0x68
    cpuidle_idle_call+0xac/0xe0
    cpu_idle+0xac/0xf0

Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Acked-by: Jassi Brar <jassisinghbrar@gmail.com>
Cc: Vinod Koul <vinod.koul@linux.intel.com>
Cc: Tomasz Figa <t.figa@samsung.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Handle big endianness in NTLM (ntlmv2) authentication

commit fdf96a907c1fbb93c633e2b7ede3b8df26d6a4c0 upstream.

This is RH bug 970891
Uppercasing of username during calculation of ntlmv2 hash fails
because UniStrupr function does not handle big endian wchars.

Also fix a comment in the same code to reflect its correct usage.

[To make it easier for stable (rather than require 2nd patch) fixed
this patch of Shirish's to remove endian warning generated
by sparse -- steve f.]

Reported-by: steve <sanpatr1@in.ibm.com>
Signed-off-by: Shirish Pargaonkar <shirishpargaonkar@gmail.com>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <smfrench@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Linux 3.4.54
ext3: fix data=journal fast mount/umount hang

commit e643692138cfa33528f054b071ba2583509bb217 upstream.

In data=journal mode, if we unmount the file system before a
transaction has a chance to complete, when the journal inode is being
evicted, we can end up calling into log_wait_commit() for the
last transaction, after the journalling machinery has been shut down.
That triggers the WARN_ONCE in __log_start_commit().

Arguably we should adjust ext3_should_journal_data() to return FALSE
for the journal inode, but the only place it matters is
ext3_evict_inode(), and so it's to save a bit of CPU time, and to make
the patch much more obviously correct by inspection(tm), we'll fix it
by explicitly not trying to waiting for a journal commit when we are
evicting the journal inode, since it's guaranteed to never succeed in
this case.

This can be easily replicated via:

     mount -t ext3 -o data=journal /dev/vdb /vdb ; umount /vdb

This is a port of ext4 fix from Ted Ts'o.

Signed-off-by: Jan Kara <jack@suse.cz>
Cc: Benjamin LaHaise <bcrl@kvack.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
libata: skip SRST for all SIMG [34]7x port-multipliers

commit 7a87718d92760fc688628ad6a430643dafa16f1f upstream.

For some reason, a lot of port-multipliers have issues with softreset.
SIMG [34]7x series port-multipliers have been quite erratic in this
regard.  I recall that it was better with some firmware revisions and
the current list of quirks worked fine for a while.  I think it got
worse with later firmwares or maybe my test coverage wasn't good
enough.  Anyways, HPA is reporting that his 3726 setup suffers SRST
failures and then the PMP gets confused and fails to probe the last
port.

The hope was that we try to stick to the standard as much as possible
and soonish the PMPs and their firmwares will improve in quality, so
the quirk list was kept to minimum.  Well, it seems like that's never
gonna happen.

Let's set NO_SRST for all [34]7x PMPs so that whatever remaining
userbase of the device suffer the least.  Maybe we should do the same
for 57xx's but unfortunately I don't have any device left to test and
I'm not even sure 57xx's have ever been made widely available, so
let's leave those alone for now.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: "H. Peter Anvin" <hpa@zytor.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
ata_piix: IDE-mode SATA patch for Intel Coleto Creek DeviceIDs

commit c7e8695bfa0611b39493a9dfe8bab9f63f9809bd upstream.

This patch adds the IDE-mode SATA DeviceIDs for the Intel Coleto Creek PCH.

Signed-off-by: Seth Heasley <seth.heasley@intel.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
ASoC: sglt5000: Fix SGTL5000_PLL_FRAC_DIV_MASK

commit 5c78dfe87ea04b501ee000a7f03b9432ac9d008c upstream.

SGTL5000_PLL_FRAC_DIV_MASK is used to mask bits 0-10 (11 bits in total) of
register CHIP_PLL_CTRL, so fix the mask to accomodate all this bit range.

Reported-by: Oskar Schirmer <oskar@scara.com>
Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Mark Brown <broonie@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
tick: Prevent uncontrolled switch to oneshot mode

commit 1f73a9806bdd07a5106409bbcab3884078bd34fe upstream.

When the system switches from periodic to oneshot mode, the broadcast
logic causes a possibility that a CPU which has not yet switched to
oneshot mode puts its own clock event device into oneshot mode without
updating the state and the timer handler.

CPU0				CPU1
				per cpu tickdev is in periodic mode
				and switched to broadcast

Switch to oneshot mode
 tick_broadcast_switch_to_oneshot()
  cpumask_copy(tick_oneshot_broacast_mask,
	       tick_broadcast_mask);

  broadcast device mode = oneshot

				Timer interrupt

				irq_enter()
				 tick_check_oneshot_broadcast()
				  dev->set_mode(ONESHOT);

				tick_handle_periodic()
				 if (dev->mode == ONESHOT)
				   dev->next_event += period;
				   FAIL.

We fail, because dev->next_event contains KTIME_MAX, if the device was
in periodic mode before the uncontrolled switch to oneshot happened.

We must copy the broadcast bits over to the oneshot mask, because
otherwise a CPU which relies on the broadcast would not been woken up
anymore after the broadcast device switched to oneshot mode.

So we need to verify in tick_check_oneshot_broadcast() whether the CPU
has already switched to oneshot mode. If not, leave the device
untouched and let the CPU switch controlled into oneshot mode.

This is a long standing bug, which was never noticed, because the main
user of the broadcast x86 cannot run into that scenario, AFAICT. The
nonarchitected timer mess of ARM creates a gazillion of differently
broken abominations which trigger the shortcomings of that broadcast
code, which better had never been necessary in the first place.

Reported-and-tested-by: Stehle Vincent-B46079 <B46079@freescale.com>
Reviewed-by: Stephen Boyd <sboyd@codeaurora.org>
Cc: John Stultz <john.stultz@linaro.org>,
Cc: Mark Rutland <mark.rutland@arm.com>
Link: http://lkml.kernel.org/r/alpine.DEB.2.02.1307012153060.4013@ionos.tec.linutronix.de
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
rt2x00: read 5GHz TX power values from the correct offset

commit 0a6f3a8ebaf13407523c2c7d575b4ca2debd23ba upstream.

The current code uses the same index value both
for the channel information array and for the TX
power table. The index starts from 14, however the
index of the TX power table must start from zero.

Fix it, in order to get the correct TX power value
for a given channel.

The changes in rt61pci.c and rt73usb.c are compile
tested only.

Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
Acked-by: Stanislaw Gruszka <stf_xl@wp.pl>
Acked-by: Gertjan van Wingerde <gwingerde@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
ath9k: Do not assign noise for NULL caldata

commit d3bcb7b24bbf09fde8405770e676fe0c11c79662 upstream.

ah->noise is maintained globally and not per-channel. This
is updated in the reset() routine after the NF history has been
filled for the *current channel*, just before switching to
the new channel. There is no need to do it inside getnf(), since
ah->noise must contain a value for the new channel.

Signed-off-by: Sujith Manoharan <c_manoha@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
SCSI: zfcp: fix adapter (re)open recovery while link to SAN is down

commit f76ccaac4f82c463a037aa4a1e4ccb85c7011814 upstream.

FCP device remains in status ERP_FAILED when device is switched online
or adapter recovery is triggered  while link to SAN is down.

When Exchange Configuration Data command returns the FSF status
FSF_EXCHANGE_CONFIG_DATA_INCOMPLETE it aborts the exchange process.
The only retries are done during the common error recovery procedure
(i.e. max. 3 retries with 8sec sleep between) and remains in status
ERP_FAILED with QDIO down.

This commit reverts the commit 0df138476c8306478d6e726f044868b4bccf411c
(zfcp: Fix adapter activation on link down).
When FSF status FSF_EXCHANGE_CONFIG_DATA_INCOMPLETE is received the
adapter recovery will be finished without any retries. QDIO will be
up now and status changes such as LINK UP will be received now.

Signed-off-by: Daniel Hansel <daniel.hansel@linux.vnet.ibm.com>
Signed-off-by: Steffen Maier <maier@linux.vnet.ibm.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
SCSI: mpt2sas: fix firmware failure with wrong task attribute

commit 48ba2efc382f94fae16ca8ca011e5961a81ad1ea upstream.

When SCSI command is received with task attribute not set, set it to SIMPLE.
Previously it is set to untagged. This causes the firmware to fail the commands.

Signed-off-by: Sreekanth Reddy <Sreekanth.Reddy@lsi.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
tracing: Use current_uid() for critical time tracing

commit f17a5194859a82afe4164e938b92035b86c55794 upstream.

The irqsoff tracer records the max time that interrupts are disabled.
There are hooks in the assembly code that calls back into the tracer when
interrupts are disabled or enabled.

When they are enabled, the tracer checks if the amount of time they
were disabled is larger than the previous recorded max interrupts off
time. If it is, it creates a snapshot of the currently running trace
to store where the last largest interrupts off time was held and how
it happened.

During testing, this RCU lockdep dump appeared:

[ 1257.829021] ===============================
[ 1257.829021] [ INFO: suspicious RCU usage. ]
[ 1257.829021] 3.10.0-rc1-test+ #171 Tainted: G        W
[ 1257.829021] -------------------------------
[ 1257.829021] /home/rostedt/work/git/linux-trace.git/include/linux/rcupdate.h:780 rcu_read_lock() used illegally while idle!
[ 1257.829021]
[ 1257.829021] other info that might help us debug this:
[ 1257.829021]
[ 1257.829021]
[ 1257.829021] RCU used illegally from idle CPU!
[ 1257.829021] rcu_scheduler_active = 1, debug_locks = 0
[ 1257.829021] RCU used illegally from extended quiescent state!
[ 1257.829021] 2 locks held by trace-cmd/4831:
[ 1257.829021]  #0:  (max_trace_lock){......}, at: [<ffffffff810e2b77>] stop_critical_timing+0x1a3/0x209
[ 1257.829021]  #1:  (rcu_read_lock){.+.+..}, at: [<ffffffff810dae5a>] __update_max_tr+0x88/0x1ee
[ 1257.829021]
[ 1257.829021] stack backtrace:
[ 1257.829021] CPU: 3 PID: 4831 Comm: trace-cmd Tainted: G        W    3.10.0-rc1-test+ #171
[ 1257.829021] Hardware name: To Be Filled By O.E.M. To Be Filled By O.E.M./To be filled by O.E.M., BIOS SDBLI944.86P 05/08/2007
[ 1257.829021]  0000000000000001 ffff880065f49da8 ffffffff8153dd2b ffff880065f49dd8
[ 1257.829021]  ffffffff81092a00 ffff88006bd78680 ffff88007add7500 0000000000000003
[ 1257.829021]  ffff88006bd78680 ffff880065f49e18 ffffffff810daebf ffffffff810dae5a
[ 1257.829021] Call Trace:
[ 1257.829021]  [<ffffffff8153dd2b>] dump_stack+0x19/0x1b
[ 1257.829021]  [<ffffffff81092a00>] lockdep_rcu_suspicious+0x109/0x112
[ 1257.829021]  [<ffffffff810daebf>] __update_max_tr+0xed/0x1ee
[ 1257.829021]  [<ffffffff810dae5a>] ? __update_max_tr+0x88/0x1ee
[ 1257.829021]  [<ffffffff811002b9>] ? user_enter+0xfd/0x107
[ 1257.829021]  [<ffffffff810dbf85>] update_max_tr_single+0x11d/0x12d
[ 1257.829021]  [<ffffffff811002b9>] ? user_enter+0xfd/0x107
[ 1257.829021]  [<ffffffff810e2b15>] stop_critical_timing+0x141/0x209
[ 1257.829021]  [<ffffffff8109569a>] ? trace_hardirqs_on+0xd/0xf
[ 1257.829021]  [<ffffffff811002b9>] ? user_enter+0xfd/0x107
[ 1257.829021]  [<ffffffff810e3057>] time_hardirqs_on+0x2a/0x2f
[ 1257.829021]  [<ffffffff811002b9>] ? user_enter+0xfd/0x107
[ 1257.829021]  [<ffffffff8109550c>] trace_hardirqs_on_caller+0x16/0x197
[ 1257.829021]  [<ffffffff8109569a>] trace_hardirqs_on+0xd/0xf
[ 1257.829021]  [<ffffffff811002b9>] user_enter+0xfd/0x107
[ 1257.829021]  [<ffffffff810029b4>] do_notify_resume+0x92/0x97
[ 1257.829021]  [<ffffffff8154bdca>] int_signal+0x12/0x17

What happened was entering into the user code, the interrupts were enabled
and a max interrupts off was recorded. The trace buffer was saved along with
various information about the task: comm, pid, uid, priority, etc.

The uid is recorded with task_uid(tsk). But this is a macro that uses rcu_read_lock()
to retrieve the data, and this happened to happen where RCU is blind (user_enter).

As only the preempt and irqs off tracers can have this happen, and they both
only have the tsk == current, if tsk == current, use current_uid() instead of
task_uid(), as current_uid() does not use RCU as only current can change its uid.

This fixes the RCU suspicious splat.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
iommu/amd: Only unmap large pages from the first pte

commit 60d0ca3cfd199b6612bbbbf4999a3470dad38bb1 upstream.

If we use a large mapping, the expectation is that only unmaps from
the first pte in the superpage are supported.  Unmaps from offsets
into the superpage should fail (ie. return zero sized unmap).  In the
current code, unmapping from an offset clears the size of the full
mapping starting from an offset.  For instance, if we map a 16k
physically contiguous range at IOVA 0x0 with a large page, then
attempt to unmap 4k at offset 12k, 4 ptes are cleared (12k - 28k) and
the unmap returns 16k unmapped.  This potentially incorrectly clears
valid mappings and confuses drivers like VFIO that use the unmap size
to release pinned pages.

Fix by refusing to unmap from offsets into the page.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Joerg Roedel <joro@8bytes.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
perf: Clone child context from parent context pmu

commit 734df5ab549ca44f40de0f07af1c8803856dfb18 upstream.

Currently when the child context for inherited events is
created, it's based on the pmu object of the first event
of the parent context.

This is wrong for the following scenario:

  - HW context having HW and SW event
  - HW event got removed (closed)
  - SW event stays in HW context as the only event
    and its pmu is used to clone the child context

The issue starts when the cpu context object is touched
based on the pmu context object (__get_cpu_context). In
this case the HW context will work with SW cpu context
ending up with following WARN below.

Fixing this by using parent context pmu object to clone
from child context.

Addresses the following warning reported by Vince Weaver:

[ 2716.472065] ------------[ cut here ]------------
[ 2716.476035] WARNING: at kernel/events/core.c:2122 task_ctx_sched_out+0x3c/0x)
[ 2716.476035] Modules linked in: nfsd auth_rpcgss oid_registry nfs_acl nfs locn
[ 2716.476035] CPU: 0 PID: 3164 Comm: perf_fuzzer Not tainted 3.10.0-rc4 #2
[ 2716.476035] Hardware name: AOpen   DE7000/nMCP7ALPx-DE R1.06 Oct.19.2012, BI2
[ 2716.476035]  0000000000000000 ffffffff8102e215 0000000000000000 ffff88011fc18
[ 2716.476035]  ffff8801175557f0 0000000000000000 ffff880119fda88c ffffffff810ad
[ 2716.476035]  ffff880119fda880 ffffffff810af02a 0000000000000009 ffff880117550
[ 2716.476035] Call Trace:
[ 2716.476035]  [<ffffffff8102e215>] ? warn_slowpath_common+0x5b/0x70
[ 2716.476035]  [<ffffffff810ab2bd>] ? task_ctx_sched_out+0x3c/0x5f
[ 2716.476035]  [<ffffffff810af02a>] ? perf_event_exit_task+0xbf/0x194
[ 2716.476035]  [<ffffffff81032a37>] ? do_exit+0x3e7/0x90c
[ 2716.476035]  [<ffffffff810cd5ab>] ? __do_fault+0x359/0x394
[ 2716.476035]  [<ffffffff81032fe6>] ? do_group_exit+0x66/0x98
[ 2716.476035]  [<ffffffff8103dbcd>] ? get_signal_to_deliver+0x479/0x4ad
[ 2716.476035]  [<ffffffff810ac05c>] ? __perf_event_task_sched_out+0x230/0x2d1
[ 2716.476035]  [<ffffffff8100205d>] ? do_signal+0x3c/0x432
[ 2716.476035]  [<ffffffff810abbf9>] ? ctx_sched_in+0x43/0x141
[ 2716.476035]  [<ffffffff810ac2ca>] ? perf_event_context_sched_in+0x7a/0x90
[ 2716.476035]  [<ffffffff810ac311>] ? __perf_event_task_sched_in+0x31/0x118
[ 2716.476035]  [<ffffffff81050dd9>] ? mmdrop+0xd/0x1c
[ 2716.476035]  [<ffffffff81051a39>] ? finish_task_switch+0x7d/0xa6
[ 2716.476035]  [<ffffffff81002473>] ? do_notify_resume+0x20/0x5d
[ 2716.476035]  [<ffffffff813654f5>] ? retint_signal+0x3d/0x78
[ 2716.476035] ---[ end trace 827178d8a5966c3d ]---

Reported-by: Vince Weaver <vincent.weaver@maine.edu>
Signed-off-by: Jiri Olsa <jolsa@redhat.com>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1373384651-6109-1-git-send-email-jolsa@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
perf: Remove WARN_ON_ONCE() check in __perf_event_enable() for valid scenario

commit 06f417968beac6e6b614e17b37d347aa6a6b1d30 upstream.

The '!ctx->is_active' check has a valid scenario, so
there's no need for the warning.

The reason is that there's a time window between the
'ctx->is_active' check in the perf_event_enable() function
and the __perf_event_enable() function having:

  - IRQs on
  - ctx->lock unlocked

where the task could be killed and 'ctx' deactivated by
perf_event_exit_task(), ending up with the warning below.

So remove the WARN_ON_ONCE() check and add comments to
explain it all.

This addresses the following warning reported by Vince Weaver:

[  324.983534] ------------[ cut here ]------------
[  324.984420] WARNING: at kernel/events/core.c:1953 __perf_event_enable+0x187/0x190()
[  324.984420] Modules linked in:
[  324.984420] CPU: 19 PID: 2715 Comm: nmi_bug_snb Not tainted 3.10.0+ #246
[  324.984420] Hardware name: Supermicro X8DTN/X8DTN, BIOS 4.6.3 01/08/2010
[  324.984420]  0000000000000009 ffff88043fce3ec8 ffffffff8160ea0b ffff88043fce3f00
[  324.984420]  ffffffff81080ff0 ffff8802314fdc00 ffff880231a8f800 ffff88043fcf7860
[  324.984420]  0000000000000286 ffff880231a8f800 ffff88043fce3f10 ffffffff8108103a
[  324.984420] Call Trace:
[  324.984420]  <IRQ>  [<ffffffff8160ea0b>] dump_stack+0x19/0x1b
[  324.984420]  [<ffffffff81080ff0>] warn_slowpath_common+0x70/0xa0
[  324.984420]  [<ffffffff8108103a>] warn_slowpath_null+0x1a/0x20
[  324.984420]  [<ffffffff81134437>] __perf_event_enable+0x187/0x190
[  324.984420]  [<ffffffff81130030>] remote_function+0x40/0x50
[  324.984420]  [<ffffffff810e51de>] generic_smp_call_function_single_interrupt+0xbe/0x130
[  324.984420]  [<ffffffff81066a47>] smp_call_function_single_interrupt+0x27/0x40
[  324.984420]  [<ffffffff8161fd2f>] call_function_single_interrupt+0x6f/0x80
[  324.984420]  <EOI>  [<ffffffff816161a1>] ? _raw_spin_unlock_irqrestore+0x41/0x70
[  324.984420]  [<ffffffff8113799d>] perf_event_exit_task+0x14d/0x210
[  324.984420]  [<ffffffff810acd04>] ? switch_task_namespaces+0x24/0x60
[  324.984420]  [<ffffffff81086946>] do_exit+0x2b6/0xa40
[  324.984420]  [<ffffffff8161615c>] ? _raw_spin_unlock_irq+0x2c/0x30
[  324.984420]  [<ffffffff81087279>] do_group_exit+0x49/0xc0
[  324.984420]  [<ffffffff81096854>] get_signal_to_deliver+0x254/0x620
[  324.984420]  [<ffffffff81043057>] do_signal+0x57/0x5a0
[  324.984420]  [<ffffffff8161a164>] ? __do_page_fault+0x2a4/0x4e0
[  324.984420]  [<ffffffff8161665c>] ? retint_restore_args+0xe/0xe
[  324.984420]  [<ffffffff816166cd>] ? retint_signal+0x11/0x84
[  324.984420]  [<ffffffff81043605>] do_notify_resume+0x65/0x80
[  324.984420]  [<ffffffff81616702>] retint_signal+0x46/0x84
[  324.984420] ---[ end trace 442ec2f04db3771a ]---

Reported-by: Vince Weaver <vincent.weaver@maine.edu>
Signed-off-by: Jiri Olsa <jolsa@redhat.com>
Suggested-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1373384651-6109-2-git-send-email-jolsa@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>