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Subject[PATCH 4.14 37/75] x86/intel_rdt: Fix potential deadlock during resctrl mount
Date
4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

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.1508490116.git.reinette.chatre@intel.com
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;
}

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