Messages in this thread Patch in this message |  | | From | "Gautham R. Shenoy" <> | Subject | [RESEND PATCH] powerpc/pseries: Fix cpu_hotplug_lock acquisition in resize_hpt | Date | Fri, 10 May 2019 14:54:54 +0530 |
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From: "Gautham R. Shenoy" <ego@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. 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
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.kumar@linux.ibm.com> Signed-off-by: Gautham R. Shenoy <ego@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 + * 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(); -- 1.9.4
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