This is a note to let you know that I've just added the patch titled

x86/intel_rdt: Fix potential deadlock during resctrl mount

to the 4.14-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: x86-intel_rdt-fix-potential-deadlock-during-resctrl-mount.patch and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From foo@baz Wed Dec 6 18:04:41 CET 2017

From: Reinette Chatre reinette.chatre@intel.com Date: Fri, 20 Oct 2017 02:16:59 -0700 Subject: x86/intel_rdt: Fix potential deadlock during resctrl mount

From: Reinette Chatre reinette.chatre@intel.com

[ Upstream commit 87943db7dfb0c5ee5aa74a9ac06346fadd9695c8 ]

Sai reported a warning during some MBA tests:

[ 236.755559] ====================================================== [ 236.762443] WARNING: possible circular locking dependency detected [ 236.769328] 4.14.0-rc4-yocto-standard #8 Not tainted [ 236.774857] ------------------------------------------------------ [ 236.781738] mount/10091 is trying to acquire lock: [ 236.787071] (cpu_hotplug_lock.rw_sem){++++}, at: [<ffffffff8117f892>] static_key_enable+0x12/0x30 [ 236.797058] but task is already holding lock: [ 236.803552] (&type->s_umount_key#37/1){+.+.}, at: [<ffffffff81208b2f>] sget_userns+0x32f/0x520 [ 236.813247] which lock already depends on the new lock.

[ 236.822353] the existing dependency chain (in reverse order) is: [ 236.830686] -> #4 (&type->s_umount_key#37/1){+.+.}: [ 236.837756] __lock_acquire+0x1100/0x11a0 [ 236.842799] lock_acquire+0xdf/0x1d0 [ 236.847363] down_write_nested+0x46/0x80 [ 236.852310] sget_userns+0x32f/0x520 [ 236.856873] kernfs_mount_ns+0x7e/0x1f0 [ 236.861728] rdt_mount+0x30c/0x440 [ 236.866096] mount_fs+0x38/0x150 [ 236.870262] vfs_kern_mount+0x67/0x150 [ 236.875015] do_mount+0x1df/0xd50 [ 236.879286] SyS_mount+0x95/0xe0 [ 236.883464] entry_SYSCALL_64_fastpath+0x18/0xad [ 236.889183] -> #3 (rdtgroup_mutex){+.+.}: [ 236.895292] __lock_acquire+0x1100/0x11a0 [ 236.900337] lock_acquire+0xdf/0x1d0 [ 236.904899] __mutex_lock+0x80/0x8f0 [ 236.909459] mutex_lock_nested+0x1b/0x20 [ 236.914407] intel_rdt_online_cpu+0x3b/0x4a0 [ 236.919745] cpuhp_invoke_callback+0xce/0xb80 [ 236.925177] cpuhp_thread_fun+0x1c5/0x230 [ 236.930222] smpboot_thread_fn+0x11a/0x1e0 [ 236.935362] kthread+0x152/0x190 [ 236.939536] ret_from_fork+0x27/0x40 [ 236.944097] -> #2 (cpuhp_state-up){+.+.}: [ 236.950199] __lock_acquire+0x1100/0x11a0 [ 236.955241] lock_acquire+0xdf/0x1d0 [ 236.959800] cpuhp_issue_call+0x12e/0x1c0 [ 236.964845] __cpuhp_setup_state_cpuslocked+0x13b/0x2f0 [ 236.971242] __cpuhp_setup_state+0xa7/0x120 [ 236.976483] page_writeback_init+0x43/0x67 [ 236.981623] pagecache_init+0x38/0x3b [ 236.986281] start_kernel+0x3c6/0x41a [ 236.990931] x86_64_start_reservations+0x2a/0x2c [ 236.996650] x86_64_start_kernel+0x72/0x75 [ 237.001793] verify_cpu+0x0/0xfb [ 237.005966] -> #1 (cpuhp_state_mutex){+.+.}: [ 237.012364] __lock_acquire+0x1100/0x11a0 [ 237.017408] lock_acquire+0xdf/0x1d0 [ 237.021969] __mutex_lock+0x80/0x8f0 [ 237.026527] mutex_lock_nested+0x1b/0x20 [ 237.031475] __cpuhp_setup_state_cpuslocked+0x54/0x2f0 [ 237.037777] __cpuhp_setup_state+0xa7/0x120 [ 237.043013] page_alloc_init+0x28/0x30 [ 237.047769] start_kernel+0x148/0x41a [ 237.052425] x86_64_start_reservations+0x2a/0x2c [ 237.058145] x86_64_start_kernel+0x72/0x75 [ 237.063284] verify_cpu+0x0/0xfb [ 237.067456] -> #0 (cpu_hotplug_lock.rw_sem){++++}: [ 237.074436] check_prev_add+0x401/0x800 [ 237.079286] __lock_acquire+0x1100/0x11a0 [ 237.084330] lock_acquire+0xdf/0x1d0 [ 237.088890] cpus_read_lock+0x42/0x90 [ 237.093548] static_key_enable+0x12/0x30 [ 237.098496] rdt_mount+0x406/0x440 [ 237.102862] mount_fs+0x38/0x150 [ 237.107035] vfs_kern_mount+0x67/0x150 [ 237.111787] do_mount+0x1df/0xd50 [ 237.116058] SyS_mount+0x95/0xe0 [ 237.120233] entry_SYSCALL_64_fastpath+0x18/0xad [ 237.125952] other info that might help us debug this:

[ 237.134867] Chain exists of: cpu_hotplug_lock.rw_sem --> rdtgroup_mutex --> &type->s_umount_key#37/1

[ 237.148425] Possible unsafe locking scenario:

[ 237.155015] CPU0 CPU1 [ 237.160057] ---- ---- [ 237.165100] lock(&type->s_umount_key#37/1); [ 237.169952] lock(rdtgroup_mutex); [ 237.176641] lock(&type->s_umount_key#37/1); [ 237.184287] lock(cpu_hotplug_lock.rw_sem); [ 237.189041] *** DEADLOCK ***

When the resctrl filesystem is mounted the locks must be acquired in the same order as was done when the cpus came online:

cpu_hotplug_lock before rdtgroup_mutex.

This also requires to switch the static_branch_enable() calls to the _cpulocked variant because now cpu hotplug lock is held already.

[ tglx: Switched to cpus_read_[un]lock ]

Reported-by: Sai Praneeth Prakhya sai.praneeth.prakhya@intel.com Signed-off-by: Reinette Chatre reinette.chatre@intel.com Tested-by: Sai Praneeth Prakhya sai.praneeth.prakhya@intel.com Acked-by: Vikas Shivappa vikas.shivappa@linux.intel.com Cc: fenghua.yu@intel.com Cc: tony.luck@intel.com Link: https://lkml.kernel.org/r/9c41b91bc2f47d9e95b62b213ecdb45623c47a9f.150849011... Signed-off-by: Thomas Gleixner tglx@linutronix.de Signed-off-by: Sasha Levin alexander.levin@verizon.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/kernel/cpu/intel_rdt_rdtgroup.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-)

--- a/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c +++ b/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c @@ -1081,6 +1081,7 @@ static struct dentry *rdt_mount(struct f struct dentry *dentry; int ret;

+ cpus_read_lock(); mutex_lock(&rdtgroup_mutex); /* * resctrl file system can only be mounted once. @@ -1130,12 +1131,12 @@ static struct dentry *rdt_mount(struct f goto out_mondata;

if (rdt_alloc_capable) - static_branch_enable(&rdt_alloc_enable_key); + static_branch_enable_cpuslocked(&rdt_alloc_enable_key); if (rdt_mon_capable) - static_branch_enable(&rdt_mon_enable_key); + static_branch_enable_cpuslocked(&rdt_mon_enable_key);

if (rdt_alloc_capable || rdt_mon_capable) - static_branch_enable(&rdt_enable_key); + static_branch_enable_cpuslocked(&rdt_enable_key);

if (is_mbm_enabled()) { r = &rdt_resources_all[RDT_RESOURCE_L3]; @@ -1157,6 +1158,7 @@ out_cdp: cdp_disable(); out: mutex_unlock(&rdtgroup_mutex); + cpus_read_unlock();

return dentry; }

Patches currently in stable-queue which might be from reinette.chatre@intel.com are

queue-4.14/x86-intel_rdt-fix-potential-deadlock-during-resctrl-mount.patch queue-4.14/x86-intel_rdt-initialize-bitmask-of-shareable-resource-if-cdp-enabled.patch