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linux/include
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Rabin Vincent e30f53aad2 tracing: Do not busy wait in buffer splice 
On a !PREEMPT kernel, attempting to use trace-cmd results in a soft
lockup:

 # trace-cmd record -e raw_syscalls:* -F false
 NMI watchdog: BUG: soft lockup - CPU#0 stuck for 22s! [trace-cmd:61]
 ...
 Call Trace:
  [<ffffffff8105b580>] ? __wake_up_common+0x90/0x90
  [<ffffffff81092e25>] wait_on_pipe+0x35/0x40
  [<ffffffff810936e3>] tracing_buffers_splice_read+0x2e3/0x3c0
  [<ffffffff81093300>] ? tracing_stats_read+0x2a0/0x2a0
  [<ffffffff812d10ab>] ? _raw_spin_unlock+0x2b/0x40
  [<ffffffff810dc87b>] ? do_read_fault+0x21b/0x290
  [<ffffffff810de56a>] ? handle_mm_fault+0x2ba/0xbd0
  [<ffffffff81095c80>] ? trace_event_buffer_lock_reserve+0x40/0x80
  [<ffffffff810951e2>] ? trace_buffer_lock_reserve+0x22/0x60
  [<ffffffff81095c80>] ? trace_event_buffer_lock_reserve+0x40/0x80
  [<ffffffff8112415d>] do_splice_to+0x6d/0x90
  [<ffffffff81126971>] SyS_splice+0x7c1/0x800
  [<ffffffff812d1edd>] tracesys_phase2+0xd3/0xd8

The problem is this: tracing_buffers_splice_read() calls
ring_buffer_wait() to wait for data in the ring buffers.  The buffers
are not empty so ring_buffer_wait() returns immediately.  But
tracing_buffers_splice_read() calls ring_buffer_read_page() with full=1,
meaning it only wants to read a full page.  When the full page is not
available, tracing_buffers_splice_read() tries to wait again with
ring_buffer_wait(), which again returns immediately, and so on.

Fix this by adding a "full" argument to ring_buffer_wait() which will
make ring_buffer_wait() wait until the writer has left the reader's
page, i.e.  until full-page reads will succeed.

Link: http://lkml.kernel.org/r/1415645194-25379-1-git-send-email-rabin@rab.in

Cc: stable@vger.kernel.org # 3.16+
Fixes: b1169cc69b ("tracing: Remove mock up poll wait function")
Signed-off-by: Rabin Vincent <rabin@rab.in>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2014-11-10 16:45:43 -05:00
..
acpi ACPI and power management updates for 3.18-rc2 2014-10-24 11:29:31 -07:00
asm-generic Merge git://git.infradead.org/users/eparis/audit 2014-10-19 16:25:56 -07:00
clocksource
crypto
drm drm/radeon: remove invalid pci id 2014-10-28 10:44:36 -04:00
dt-bindings ARM: imx: clk-vf610: define PLL's clock tree 2014-11-04 13:40:14 +08:00
keys
kvm arm/arm64: KVM: Fix BE accesses to GICv2 EISR and ELRSR regs 2014-10-16 10:57:41 +02:00
linux tracing: Do not busy wait in buffer splice 2014-11-10 16:45:43 -05:00
math-emu
media
memory
misc
net Merge git://git.kernel.org/pub/scm/linux/kernel/git/pablo/nf 2014-10-31 12:29:42 -04:00
pcmcia
ras
rdma
rxrpc
scsi scsi: set REQ_QUEUE for the blk-mq case 2014-10-28 09:53:43 +01:00
soc/tegra
sound Merge branch 'for-linus' of git://git.infradead.org/users/vkoul/slave-dma 2014-10-18 18:11:04 -07:00
target
trace Merge branch 'urgent-for-mingo' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu into core/urgent 2014-10-30 07:37:37 +01:00
uapi Merge branch 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2014-10-31 14:05:35 -07:00
video fbdev changes for 3.18 2014-10-18 18:03:02 -07:00
xen
Kbuild