lwn.git/arch/s390/kernel/smp.c, branch docs-5.3-1

s390: improve wait logic of stop_machine

2019-06-15T10:25:52+00:00

The stop_machine loop to advance the state machine and to wait for all affected CPUs to check-in calls cpu_relax_yield in a tight loop until the last missing CPUs acknowledged the state transition. On a virtual system where not all logical CPUs are backed by real CPUs all the time it can take a while for all CPUs to check-in. With the current definition of cpu_relax_yield a diagnose 0x44 is done which tells the hypervisor to schedule *some* other CPU. That can be any CPU and not necessarily one of the CPUs that need to run in order to advance the state machine. This can lead to a pretty bad diagnose 0x44 storm until the last missing CPU finally checked-in. Replace the undirected cpu_relax_yield based on diagnose 0x44 with a directed yield. Each CPU in the wait loop will pick up the next CPU in the cpumask of stop_machine. The diagnose 0x9c is used to tell the hypervisor to run this next CPU instead of the current one. If there is only a limited number of real CPUs backing the virtual CPUs we end up with the real CPUs passed around in a round-robin fashion. [heiko.carstens@de.ibm.com]: Use cpumask_next_wrap as suggested by Peter Zijlstra. Signed-off-by: Martin Schwidefsky Acked-by: Peter Zijlstra (Intel) Acked-by: Thomas Gleixner Signed-off-by: Heiko Carstens

s390: enforce CONFIG_HOTPLUG_CPU

2019-06-07T08:09:42+00:00

x86 and powerpc (partially) enforce already CONFIG_HOTPLUG_CPU. On s390 it is enabled on all distributions by default since ages. The only exception is our zfcpdump kernel. However to simplify testing, enforce HOTPLUG_CPU. This was suggested by Paul McKenney, since his rcutorture test environments for CONFIG_SMP=y only support HOTPLUG_CPU=y. Suggested-by: Paul E. McKenney Acked-by: Christian Borntraeger Signed-off-by: Heiko Carstens

s390/unwind: introduce stack unwind API

2019-05-02T11:54:11+00:00

Rework the dump_trace() stack unwinder interface to support different unwinding algorithms. The new interface looks like this: struct unwind_state state; unwind_for_each_frame(&state, task, regs, start_stack) do_something(state.sp, state.ip, state.reliable); The unwind_bc.c file contains the implementation for the classic back-chain unwinder. One positive side effect of the new code is it now handles ftraced functions gracefully. It prints the real name of the return function instead of 'return_to_handler'. Signed-off-by: Martin Schwidefsky

s390/kernel: introduce .dma sections

2019-04-29T08:47:10+00:00

With a relocatable kernel that could reside at any place in memory, code and data that has to stay below 2 GB needs special handling. This patch introduces .dma sections for such text, data and ex_table. The sections will be part of the decompressor kernel, so they will not be relocated and stay below 2 GB. Their location is passed over to the decompressed / relocated kernel via the .boot.preserved.data section. The duald and aste for control register setup also need to stay below 2 GB, so move the setup code from arch/s390/kernel/head64.S to arch/s390/boot/head.S. The duct and linkage_stack could reside above 2 GB, but their content has to be preserved for the decompresed kernel, so they are also moved into the .dma section. The start and end address of the .dma sections is added to vmcoreinfo, for crash support, to help debugging in case the kernel crashed there. Signed-off-by: Gerald Schaefer Reviewed-by: Philipp Rudo Signed-off-by: Martin Schwidefsky

Merge tag 's390-5.1-2' of git://git.kernel.org/pub/scm/linux/kernel/git/s390/linux

2019-03-28T15:35:32+00:00

Pull s390 fixes from Martin Schwidefsky: "Improvements and bug fixes for 5.1-rc2: - Fix early free of the channel program in vfio - On AP device removal make sure that all messages are flushed with the driver still attached that queued the message - Limit brk randomization to 32MB to reduce the chance that the heap of ld.so is placed after the main stack - Add a rolling average for the steal time of a CPU, this will be needed for KVM to decide when to do busy waiting - Fix a warning in the CPU-MF code - Add a notification handler for AP configuration change to react faster to new AP devices" * tag 's390-5.1-2' of git://git.kernel.org/pub/scm/linux/kernel/git/s390/linux: s390/cpumf: Fix warning from check_processor_id zcrypt: handle AP Info notification from CHSC SEI command vfio: ccw: only free cp on final interrupt s390/vtime: steal time exponential moving average s390/zcrypt: revisit ap device remove procedure s390: limit brk randomization to 32MB

treewide: add checks for the return value of memblock_alloc*()

2019-03-12T17:04:02+00:00

Add check for the return value of memblock_alloc*() functions and call panic() in case of error. The panic message repeats the one used by panicing memblock allocators with adjustment of parameters to include only relevant ones. The replacement was mostly automated with semantic patches like the one below with manual massaging of format strings. @@ expression ptr, size, align; @@ ptr = memblock_alloc(size, align); + if (!ptr) + panic("%s: Failed to allocate %lu bytes align=0x%lx\n", __func__, size, align); [anders.roxell@linaro.org: use '%pa' with 'phys_addr_t' type] Link: http://lkml.kernel.org/r/20190131161046.21886-1-anders.roxell@linaro.org [rppt@linux.ibm.com: fix format strings for panics after memblock_alloc] Link: http://lkml.kernel.org/r/1548950940-15145-1-git-send-email-rppt@linux.ibm.com [rppt@linux.ibm.com: don't panic if the allocation in sparse_buffer_init fails] Link: http://lkml.kernel.org/r/20190131074018.GD28876@rapoport-lnx [akpm@linux-foundation.org: fix xtensa printk warning] Link: http://lkml.kernel.org/r/1548057848-15136-20-git-send-email-rppt@linux.ibm.com Signed-off-by: Mike Rapoport Signed-off-by: Anders Roxell Reviewed-by: Guo Ren [c-sky] Acked-by: Paul Burton [MIPS] Acked-by: Heiko Carstens [s390] Reviewed-by: Juergen Gross [Xen] Reviewed-by: Geert Uytterhoeven [m68k] Acked-by: Max Filippov [xtensa] Cc: Catalin Marinas Cc: Christophe Leroy Cc: Christoph Hellwig Cc: "David S. Miller" Cc: Dennis Zhou Cc: Greentime Hu Cc: Greg Kroah-Hartman Cc: Guan Xuetao Cc: Guo Ren Cc: Mark Salter Cc: Matt Turner Cc: Michael Ellerman Cc: Michal Simek Cc: Petr Mladek Cc: Richard Weinberger Cc: Rich Felker Cc: Rob Herring Cc: Rob Herring Cc: Russell King Cc: Stafford Horne Cc: Tony Luck Cc: Vineet Gupta Cc: Yoshinori Sato Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

memblock: drop memblock_alloc_base()

2019-03-12T17:04:01+00:00

The memblock_alloc_base() function tries to allocate a memory up to the limit specified by its max_addr parameter and panics if the allocation fails. Replace its usage with memblock_phys_alloc_range() and make the callers check the return value and panic in case of error. Link: http://lkml.kernel.org/r/1548057848-15136-10-git-send-email-rppt@linux.ibm.com Signed-off-by: Mike Rapoport Acked-by: Michael Ellerman [powerpc] Cc: Catalin Marinas Cc: Christophe Leroy Cc: Christoph Hellwig Cc: "David S. Miller" Cc: Dennis Zhou Cc: Geert Uytterhoeven Cc: Greentime Hu Cc: Greg Kroah-Hartman Cc: Guan Xuetao Cc: Guo Ren Cc: Guo Ren [c-sky] Cc: Heiko Carstens Cc: Juergen Gross [Xen] Cc: Mark Salter Cc: Matt Turner Cc: Max Filippov Cc: Michael Ellerman Cc: Michal Simek Cc: Paul Burton Cc: Petr Mladek Cc: Richard Weinberger Cc: Rich Felker Cc: Rob Herring Cc: Rob Herring Cc: Russell King Cc: Stafford Horne Cc: Tony Luck Cc: Vineet Gupta Cc: Yoshinori Sato Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

s390/vtime: steal time exponential moving average

2019-03-06T13:59:50+00:00

To be able to judge the current overcommitment ratio for a CPU add a lowcore field with the exponential moving average of the steal time. The average is updated every tick. Signed-off-by: Martin Schwidefsky

s390/smp: Fix calling smp_call_ipl_cpu() from ipl CPU

2019-01-11T16:12:03+00:00

When calling smp_call_ipl_cpu() from the IPL CPU, we will try to read from pcpu_devices->lowcore. However, due to prefixing, that will result in reading from absolute address 0 on that CPU. We have to go via the actual lowcore instead. This means that right now, we will read lc->nodat_stack == 0 and therfore work on a very wrong stack. This BUG essentially broke rebooting under QEMU TCG (which will report a low address protection exception). And checking under KVM, it is also broken under KVM. With 1 VCPU it can be easily triggered. :/# echo 1 > /proc/sys/kernel/sysrq :/# echo b > /proc/sysrq-trigger [ 28.476745] sysrq: SysRq : Resetting [ 28.476793] Kernel stack overflow. [ 28.476817] CPU: 0 PID: 424 Comm: sh Not tainted 5.0.0-rc1+ #13 [ 28.476820] Hardware name: IBM 2964 NE1 716 (KVM/Linux) [ 28.476826] Krnl PSW : 0400c00180000000 0000000000115c0c (pcpu_delegate+0x12c/0x140) [ 28.476861] R:0 T:1 IO:0 EX:0 Key:0 M:0 W:0 P:0 AS:3 CC:0 PM:0 RI:0 EA:3 [ 28.476863] Krnl GPRS: ffffffffffffffff 0000000000000000 000000000010dff8 0000000000000000 [ 28.476864] 0000000000000000 0000000000000000 0000000000ab7090 000003e0006efbf0 [ 28.476864] 000000000010dff8 0000000000000000 0000000000000000 0000000000000000 [ 28.476865] 000000007fffc000 0000000000730408 000003e0006efc58 0000000000000000 [ 28.476887] Krnl Code: 0000000000115bfe: 4170f000 la %r7,0(%r15) [ 28.476887] 0000000000115c02: 41f0a000 la %r15,0(%r10) [ 28.476887] #0000000000115c06: e370f0980024 stg %r7,152(%r15) [ 28.476887] >0000000000115c0c: c0e5fffff86e brasl %r14,114ce8 [ 28.476887] 0000000000115c12: 41f07000 la %r15,0(%r7) [ 28.476887] 0000000000115c16: a7f4ffa8 brc 15,115b66 [ 28.476887] 0000000000115c1a: 0707 bcr 0,%r7 [ 28.476887] 0000000000115c1c: 0707 bcr 0,%r7 [ 28.476901] Call Trace: [ 28.476902] Last Breaking-Event-Address: [ 28.476920] [<0000000000a01c4a>] arch_call_rest_init+0x22/0x80 [ 28.476927] Kernel panic - not syncing: Corrupt kernel stack, can't continue. [ 28.476930] CPU: 0 PID: 424 Comm: sh Not tainted 5.0.0-rc1+ #13 [ 28.476932] Hardware name: IBM 2964 NE1 716 (KVM/Linux) [ 28.476932] Call Trace: Fixes: 2f859d0dad81 ("s390/smp: reduce size of struct pcpu") Cc: stable@vger.kernel.org # 4.0+ Reported-by: Cornelia Huck Signed-off-by: David Hildenbrand Signed-off-by: Martin Schwidefsky

s390/smp: fix CPU hotplug deadlock with CPU rescan

2019-01-11T16:12:02+00:00

smp_rescan_cpus() is called without the device_hotplug_lock, which can lead to a dedlock when a new CPU is found and immediately set online by a udev rule. This was observed on an older kernel version, where the cpu_hotplug_begin() loop was still present, and it resulted in hanging chcpu and systemd-udev processes. This specific deadlock will not show on current kernels. However, there may be other possible deadlocks, and since smp_rescan_cpus() can still trigger a CPU hotplug operation, the device_hotplug_lock should be held. For reference, this was the deadlock with the old cpu_hotplug_begin() loop: chcpu (rescan) systemd-udevd echo 1 > /sys/../rescan -> smp_rescan_cpus() -> (*) get_online_cpus() (increases refcount) -> smp_add_present_cpu() (new CPU found) -> register_cpu() -> device_add() -> udev "add" event triggered -----------> udev rule sets CPU online -> echo 1 > /sys/.../online -> lock_device_hotplug_sysfs() (this is missing in rescan path) -> device_online() -> (**) device_lock(new CPU dev) -> cpu_up() -> cpu_hotplug_begin() (loops until refcount == 0) -> deadlock with (*) -> bus_probe_device() -> device_attach() -> device_lock(new CPU dev) -> deadlock with (**) Fix this by taking the device_hotplug_lock in the CPU rescan path. Cc: Signed-off-by: Gerald Schaefer Signed-off-by: Martin Schwidefsky