linux.git/arch/powerpc/kernel/smp.c, branch v3.12.65

powerpc/smp: Wait until secondaries are active & online

2015-04-09T12:13:43+00:00

commit 875ebe940d77a41682c367ad799b4f39f128d3fa upstream.

Anton has a busy ppc64le KVM box where guests sometimes hit the infamous
"kernel BUG at kernel/smpboot.c:134!" issue during boot:

  BUG_ON(td->cpu != smp_processor_id());

Basically a per CPU hotplug thread scheduled on the wrong CPU. The oops
output confirms it:

  CPU: 0
  Comm: watchdog/130

The problem is that we aren't ensuring the CPU active bit is set for the
secondary before allowing the master to continue on. The master unparks
the secondary CPU's kthreads and the scheduler looks for a CPU to run
on. It calls select_task_rq() and realises the suggested CPU is not in
the cpus_allowed mask. It then ends up in select_fallback_rq(), and
since the active bit isnt't set we choose some other CPU to run on.

This seems to have been introduced by 6acbfb96976f "sched: Fix hotplug
vs. set_cpus_allowed_ptr()", which changed from setting active before
online to setting active after online. However that was in turn fixing a
bug where other code assumed an active CPU was also online, so we can't
just revert that fix.

The simplest fix is just to spin waiting for both active & online to be
set. We already have a barrier prior to set_cpu_online() (which also
sets active), to ensure all other setup is completed before online &
active are set.

Fixes: 6acbfb96976f ("sched: Fix hotplug vs. set_cpus_allowed_ptr()")
Signed-off-by: Michael Ellerman 
Signed-off-by: Anton Blanchard 
Signed-off-by: Michael Ellerman 
Signed-off-by: Jiri Slaby

powerpc: Export cpu_to_chip_id() to fix build error

2013-09-11T01:39:37+00:00

powerpc allmodconfig build fails with:

ERROR: ".cpu_to_chip_id" [drivers/block/mtip32xx/mtip32xx.ko] undefined!

The problem was introduced with commit 15863ff3b (powerpc: Make chip-id
information available to userspace).

Export the missing symbol.

Cc: Vasant Hegde 
Cc: Shivaprasad G Bhat 
Signed-off-by: Guenter Roeck 
Signed-off-by: Benjamin Herrenschmidt

powerpc: Little endian SMP IPI demux

2013-08-14T05:33:37+00:00

Add little endian support for demuxing SMP IPIs

Signed-off-by: Anton Blanchard 
Signed-off-by: Benjamin Herrenschmidt

powerpc: Make chip-id information available to userspace

2013-08-14T05:33:17+00:00

So far "/sys/devices/system/cpu/cpuX/topology/physical_package_id"
was always default (-1) on ppc64 architecture.

Now, some systems have an ibm,chip-id property in the cpu nodes in
the device tree. On these systems, we now use this information to
display physical_package_id.

Signed-off-by: Vasant Hegde 
Signed-off-by: Shivaprasad G Bhat 
Signed-off-by: Benjamin Herrenschmidt

powerpc: Use ibm, chip-id property to compute cpu_core_mask if available

2013-08-14T05:00:22+00:00

Some systems have an ibm,chip-id property in the cpu nodes in the
device tree.  On these systems, we now use that to compute the
cpu_core_mask (i.e. the set of core siblings) rather than looking
at cache properties.

Signed-off-by: Paul Mackerras 
Tested-by: Vasant Hegde 
Signed-off-by: Benjamin Herrenschmidt

powerpc: Pull out cpu_core_mask updates into a separate function

2013-08-14T05:00:16+00:00

This factors out the details of updating cpu_core_mask into a separate
function, to make it easier to change how the mask is calculated later.
This makes no functional change.

Signed-off-by: Paul Mackerras 
Signed-off-by: Benjamin Herrenschmidt

powerpc: Add smp_generic_cpu_bootable

2013-08-14T04:56:50+00:00

Cell and PSeries both implemented their own versions of a
cpu_bootable smp_op which do the same thing (well, the PSeries
one has support for more than 2 threads). Copy the PSeries one
to generic code, and rename it smp_generic_cpu_bootable.

Signed-off-by: Andy Fleming 
Signed-off-by: Benjamin Herrenschmidt

powerpc: Fix a number of sparse warnings

2013-08-14T01:50:24+00:00

Address some of the trivial sparse warnings in arch/powerpc.

Signed-off-by: Anton Blanchard 
Signed-off-by: Benjamin Herrenschmidt

powerpc: Set cpu sibling mask before online cpu

2013-07-01T01:46:55+00:00

It seems following race is possible:

	cpu0					cpux
smp_init->cpu_up->_cpu_up
	__cpu_up
		kick_cpu(1)
-------------------------------------------------------------------------
		waiting online			...
		...				notify CPU_STARTING
							set cpux active
						set cpux online
-------------------------------------------------------------------------
		finish waiting online
		...
sched_init_smp
	init_sched_domains(cpu_active_mask)
		build_sched_domains
						set cpux sibling info
-------------------------------------------------------------------------

Execution of cpu0 and cpux could be concurrent between two separator
lines.

So if the cpux sibling information was set too late (normally
impossible, but could be triggered by adding some delay in
start_secondary, after setting cpu online), build_sched_domains()
running on cpu0 might see cpux active, with an empty sibling mask, then
cause some bad address accessing like following:

[    0.099855] Unable to handle kernel paging request for data at address 0xc00000038518078f
[    0.099868] Faulting instruction address: 0xc0000000000b7a64
[    0.099883] Oops: Kernel access of bad area, sig: 11 [#1]
[    0.099895] PREEMPT SMP NR_CPUS=16 DEBUG_PAGEALLOC NUMA pSeries
[    0.099922] Modules linked in:
[    0.099940] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 3.10.0-rc1-00120-gb973425-dirty #16
[    0.099956] task: c0000001fed80000 ti: c0000001fed7c000 task.ti: c0000001fed7c000
[    0.099971] NIP: c0000000000b7a64 LR: c0000000000b7a40 CTR: c0000000000b4934
[    0.099985] REGS: c0000001fed7f760 TRAP: 0300   Not tainted  (3.10.0-rc1-00120-gb973425-dirty)
[    0.099997] MSR: 8000000000009032   CR: 24272828  XER: 20000003
[    0.100045] SOFTE: 1
[    0.100053] CFAR: c000000000445ee8
[    0.100064] DAR: c00000038518078f, DSISR: 40000000
[    0.100073]
GPR00: 0000000000000080 c0000001fed7f9e0 c000000000c84d48 0000000000000010
GPR04: 0000000000000010 0000000000000000 c0000001fc55e090 0000000000000000
GPR08: ffffffffffffffff c000000000b80b30 c000000000c962d8 00000003845ffc5f
GPR12: 0000000000000000 c00000000f33d000 c00000000000b9e4 0000000000000000
GPR16: 0000000000000000 0000000000000000 0000000000000001 0000000000000000
GPR20: c000000000ccf750 0000000000000000 c000000000c94d48 c0000001fc504000
GPR24: c0000001fc504000 c0000001fecef848 c000000000c94d48 c000000000ccf000
GPR28: c0000001fc522090 0000000000000010 c0000001fecef848 c0000001fed7fae0
[    0.100293] NIP [c0000000000b7a64] .get_group+0x84/0xc4
[    0.100307] LR [c0000000000b7a40] .get_group+0x60/0xc4
[    0.100318] Call Trace:
[    0.100332] [c0000001fed7f9e0] [c0000000000dbce4] .lock_is_held+0xa8/0xd0 (unreliable)
[    0.100354] [c0000001fed7fa70] [c0000000000bf62c] .build_sched_domains+0x728/0xd14
[    0.100375] [c0000001fed7fbe0] [c000000000af67bc] .sched_init_smp+0x4fc/0x654
[    0.100394] [c0000001fed7fce0] [c000000000adce24] .kernel_init_freeable+0x17c/0x30c
[    0.100413] [c0000001fed7fdb0] [c00000000000ba08] .kernel_init+0x24/0x12c
[    0.100431] [c0000001fed7fe30] [c000000000009f74] .ret_from_kernel_thread+0x5c/0x68
[    0.100445] Instruction dump:
[    0.100456] 38800010 38a00000 4838e3f5 60000000 7c6307b4 2fbf0000 419e0040 3d220001
[    0.100496] 78601f24 39491590 e93e0008 7d6a002a <7d69582a> f97f0000 7d4a002a e93e0010
[    0.100559] ---[ end trace 31fd0ba7d8756001 ]---

This patch tries to move the sibling maps updating before
notify_cpu_starting() and cpu online, and a write barrier there to make
sure sibling maps are updated before active and online mask.

Signed-off-by: Li Zhong 
Reviewed-by: Srivatsa S. Bhat 
Signed-off-by: Benjamin Herrenschmidt

powerpc: Delete __cpuinit usage from all users

2013-07-01T01:10:36+00:00

The __cpuinit type of throwaway sections might have made sense
some time ago when RAM was more constrained, but now the savings
do not offset the cost and complications.  For example, the fix in
commit 5e427ec2d0 ("x86: Fix bit corruption at CPU resume time")
is a good example of the nasty type of bugs that can be created
with improper use of the various __init prefixes.

After a discussion on LKML[1] it was decided that cpuinit should go
the way of devinit and be phased out.  Once all the users are gone,
we can then finally remove the macros themselves from linux/init.h.

This removes all the powerpc uses of the __cpuinit macros.  There
are no __CPUINIT users in assembly files in powerpc.

[1] https://lkml.org/lkml/2013/5/20/589

Cc: Benjamin Herrenschmidt 
Cc: Paul Mackerras 
Cc: Josh Boyer 
Cc: Matt Porter 
Cc: Kumar Gala 
Cc: linuxppc-dev@lists.ozlabs.org
Signed-off-by: Paul Gortmaker 
Signed-off-by: Benjamin Herrenschmidt