Hi Michael, On Tue, May 14, 2019 at 05:00:19PM +1000, Michael Ellerman wrote: > "Gautham R. Shenoy" <e...@linux.vnet.ibm.com> writes: > > From: "Gautham R. Shenoy" <e...@linux.vnet.ibm.com> > > > > During a memory hotplug operations involving resizing of the HPT, we > > invoke a stop_machine() to perform the resizing. In this code path, we > > end up recursively taking the cpu_hotplug_lock, first in > > memory_hotplug_begin() and then subsequently in stop_machine(). This > > causes the system to hang. > > This implies we have never tested a memory hotplug that resized the HPT. > Is that really true? Or did something change? >
This was reported by Aneesh during a testcase involving reconfiguring the namespace for nvdimm where we do a memory remove followed by add. The memory add invokes resize_hpt(). It seems we can hit this issue when we perform a memory hotplug/unplug in the guest. > > With lockdep enabled we get the following > > error message before the hang. > > > > swapper/0/1 is trying to acquire lock: > > (____ptrval____) (cpu_hotplug_lock.rw_sem){++++}, at: > > stop_machine+0x2c/0x60 > > > > but task is already holding lock: > > (____ptrval____) (cpu_hotplug_lock.rw_sem){++++}, at: > > mem_hotplug_begin+0x20/0x50 > > Do we have the full stack trace? Yes, here is the complete log: [ 0.537123] swapper/0/1 is trying to acquire lock: [ 0.537197] (____ptrval____) (cpu_hotplug_lock.rw_sem){++++}, at: stop_machine+0x2c/0x60 [ 0.537336] [ 0.537336] but task is already holding lock: [ 0.537429] (____ptrval____) (cpu_hotplug_lock.rw_sem){++++}, at: mem_hotplug_begin+0x20/0x50 [ 0.537570] [ 0.537570] other info that might help us debug this: [ 0.537663] Possible unsafe locking scenario: [ 0.537663] [ 0.537756] CPU0 [ 0.537794] ---- [ 0.537832] lock(cpu_hotplug_lock.rw_sem); [ 0.537906] lock(cpu_hotplug_lock.rw_sem); [ 0.537980] [ 0.537980] *** DEADLOCK *** [ 0.537980] [ 0.538074] May be due to missing lock nesting notation [ 0.538074] [ 0.538168] 3 locks held by swapper/0/1: [ 0.538224] #0: (____ptrval____) (&dev->mutex){....}, at: __driver_attach+0x12c/0x1b0 [ 0.538348] #1: (____ptrval____) (cpu_hotplug_lock.rw_sem){++++}, at: mem_hotplug_begin+0x20/0x50 [ 0.538477] #2: (____ptrval____) (mem_hotplug_lock.rw_sem){++++}, at: percpu_down_write+0x54/0x1a0 [ 0.538608] [ 0.538608] stack backtrace: [ 0.538685] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.0.0-rc5-58373-gbc99402235f3-dirty #166 [ 0.538812] Call Trace: [ 0.538863] [c0000000feb03150] [c000000000e32bd4] dump_stack+0xe8/0x164 (unreliable) [ 0.538975] [c0000000feb031a0] [c00000000020d6c0] __lock_acquire+0x1110/0x1c70 [ 0.539086] [c0000000feb03320] [c00000000020f080] lock_acquire+0x240/0x290 [ 0.539180] [c0000000feb033e0] [c00000000017f554] cpus_read_lock+0x64/0xf0 [ 0.539273] [c0000000feb03420] [c00000000029ebac] stop_machine+0x2c/0x60 [ 0.539367] [c0000000feb03460] [c0000000000d7f7c] pseries_lpar_resize_hpt+0x19c/0x2c0 [ 0.539479] [c0000000feb03500] [c0000000000788d0] resize_hpt_for_hotplug+0x70/0xd0 [ 0.539590] [c0000000feb03570] [c000000000e5d278] arch_add_memory+0x58/0xfc [ 0.539683] [c0000000feb03610] [c0000000003553a8] devm_memremap_pages+0x5e8/0x8f0 [ 0.539804] [c0000000feb036c0] [c0000000009c2394] pmem_attach_disk+0x764/0x830 [ 0.539916] [c0000000feb037d0] [c0000000009a7c38] nvdimm_bus_probe+0x118/0x240 [ 0.540026] [c0000000feb03860] [c000000000968500] really_probe+0x230/0x4b0 [ 0.540119] [c0000000feb038f0] [c000000000968aec] driver_probe_device+0x16c/0x1e0 [ 0.540230] [c0000000feb03970] [c000000000968ca8] __driver_attach+0x148/0x1b0 [ 0.540340] [c0000000feb039f0] [c0000000009650b0] bus_for_each_dev+0x90/0x130 [ 0.540451] [c0000000feb03a50] [c000000000967dd4] driver_attach+0x34/0x50 [ 0.540544] [c0000000feb03a70] [c000000000967068] bus_add_driver+0x1a8/0x360 [ 0.540654] [c0000000feb03b00] [c00000000096a498] driver_register+0x108/0x170 [ 0.540766] [c0000000feb03b70] [c0000000009a7400] __nd_driver_register+0xd0/0xf0 [ 0.540898] [c0000000feb03bd0] [c00000000128aa90] nd_pmem_driver_init+0x34/0x48 [ 0.541010] [c0000000feb03bf0] [c000000000010a10] do_one_initcall+0x1e0/0x45c [ 0.541122] [c0000000feb03cd0] [c00000000122462c] kernel_init_freeable+0x540/0x64c [ 0.541232] [c0000000feb03db0] [c00000000001110c] kernel_init+0x2c/0x160 [ 0.541326] [c0000000feb03e20] [c00000000000bed4] ret_from_kernel_thread+0x5c/0x68 > > > other info that might help us debug this: > > Possible unsafe locking scenario: > > > > CPU0 > > ---- > > lock(cpu_hotplug_lock.rw_sem); > > lock(cpu_hotplug_lock.rw_sem); > > > > *** DEADLOCK *** > > > > Fix this issue by > > 1) Requiring all the calls to pseries_lpar_resize_hpt() be made > > with cpu_hotplug_lock held. > > > > 2) In pseries_lpar_resize_hpt() invoke stop_machine_cpuslocked() > > as a consequence of 1) > > > > 3) To satisfy 1), in hpt_order_set(), call mmu_hash_ops.resize_hpt() > > with cpu_hotplug_lock held. > > > > Reported-by: Aneesh Kumar K.V <aneesh.ku...@linux.ibm.com> > > Signed-off-by: Gautham R. Shenoy <e...@linux.vnet.ibm.com> > > --- > > > > Rebased this one against powerpc/next instead of linux/master. > > > > arch/powerpc/mm/book3s64/hash_utils.c | 9 ++++++++- > > arch/powerpc/platforms/pseries/lpar.c | 8 ++++++-- > > 2 files changed, 14 insertions(+), 3 deletions(-) > > > > diff --git a/arch/powerpc/mm/book3s64/hash_utils.c > > b/arch/powerpc/mm/book3s64/hash_utils.c > > index 919a861..d07fcafd 100644 > > --- a/arch/powerpc/mm/book3s64/hash_utils.c > > +++ b/arch/powerpc/mm/book3s64/hash_utils.c > > @@ -38,6 +38,7 @@ > > #include <linux/libfdt.h> > > #include <linux/pkeys.h> > > #include <linux/hugetlb.h> > > +#include <linux/cpu.h> > > > > #include <asm/debugfs.h> > > #include <asm/processor.h> > > @@ -1928,10 +1929,16 @@ static int hpt_order_get(void *data, u64 *val) > > > > static int hpt_order_set(void *data, u64 val) > > { > > + int ret; > > + > > if (!mmu_hash_ops.resize_hpt) > > return -ENODEV; > > > > - return mmu_hash_ops.resize_hpt(val); > > + cpus_read_lock(); > > + ret = mmu_hash_ops.resize_hpt(val); > > + cpus_read_unlock(); > > + > > + return ret; > > } > > > > DEFINE_DEBUGFS_ATTRIBUTE(fops_hpt_order, hpt_order_get, hpt_order_set, > > "%llu\n"); > > diff --git a/arch/powerpc/platforms/pseries/lpar.c > > b/arch/powerpc/platforms/pseries/lpar.c > > index 1034ef1..2fc9756 100644 > > --- a/arch/powerpc/platforms/pseries/lpar.c > > +++ b/arch/powerpc/platforms/pseries/lpar.c > > @@ -859,7 +859,10 @@ static int pseries_lpar_resize_hpt_commit(void *data) > > return 0; > > } > > > > -/* Must be called in user context */ > > +/* > > + * Must be called in user context. The caller should hold the > > I realise you're just copying that comment, but it seems wrong. "user > context" means userspace. I think it means "process context" doesn't it? > Yes, from the qemu process context. I will fix this part of the comment and also change the should to must. > Also "should" should be "must" :) > Thanks for the review. > > + * cpus_lock. > > + */ > > static int pseries_lpar_resize_hpt(unsigned long shift) > > { > > struct hpt_resize_state state = { > > @@ -913,7 +916,8 @@ static int pseries_lpar_resize_hpt(unsigned long shift) > > > > t1 = ktime_get(); > > > > - rc = stop_machine(pseries_lpar_resize_hpt_commit, &state, NULL); > > + rc = stop_machine_cpuslocked(pseries_lpar_resize_hpt_commit, > > + &state, NULL); > > > > t2 = ktime_get(); > > cheers >