On Mon, Oct 05, 2015 at 02:32:51PM -0700, Yang Shi wrote:

BUG: sleeping function called from invalid context at kernel/locking/rtmutex.c:917 in_atomic(): 0, irqs_disabled(): 128, pid: 342, name: perf 1 lock held by perf/342: #0: (break_hook_lock){+.+...}, at: [<ffffffc0000851ac>] call_break_hook+0x34/0xd0 irq event stamp: 62224 hardirqs last enabled at (62223): [<ffffffc00010b7bc>] __call_rcu.constprop.59+0x104/0x270 hardirqs last disabled at (62224): [<ffffffc0000fbe20>] vprintk_emit+0x68/0x640 softirqs last enabled at (0): [<ffffffc000097928>] copy_process.part.8+0x428/0x17f8 softirqs last disabled at (0): [< (null)>] (null) CPU: 0 PID: 342 Comm: perf Not tainted 4.1.6-rt5 #4 Hardware name: linux,dummy-virt (DT) Call trace: [<ffffffc000089968>] dump_backtrace+0x0/0x128 [<ffffffc000089ab0>] show_stack+0x20/0x30 [<ffffffc0007030d0>] dump_stack+0x7c/0xa0 [<ffffffc0000c878c>] ___might_sleep+0x174/0x260 [<ffffffc000708ac8>] __rt_spin_lock+0x28/0x40 [<ffffffc000708db0>] rt_read_lock+0x60/0x80 [<ffffffc0000851a8>] call_break_hook+0x30/0xd0 [<ffffffc000085a70>] brk_handler+0x30/0x98 [<ffffffc000082248>] do_debug_exception+0x50/0xb8 Exception stack(0xffffffc00514fe30 to 0xffffffc00514ff50) fe20: 00000000 00000000 c1594680 0000007f fe40: ffffffff ffffffff 92063940 0000007f 0550dcd8 ffffffc0 00000000 00000000 fe60: 0514fe70 ffffffc0 000be1f8 ffffffc0 0514feb0 ffffffc0 0008948c ffffffc0 fe80: 00000004 00000000 0514fed0 ffffffc0 ffffffff ffffffff 9282a948 0000007f fea0: 00000000 00000000 9282b708 0000007f c1592820 0000007f 00083914 ffffffc0 fec0: 00000000 00000000 00000010 00000000 00000064 00000000 00000001 00000000 fee0: 005101e0 00000000 c1594680 0000007f c1594740 0000007f ffffffd8 ffffff80 ff00: 00000000 00000000 00000000 00000000 c1594770 0000007f c1594770 0000007f ff20: 00665e10 00000000 7f7f7f7f 7f7f7f7f 01010101 01010101 00000000 00000000 ff40: 928e4cc0 0000007f 91ff11e8 0000007f

call_break_hook is called in atomic context (hard irq disabled), so replace the sleepable lock to rcu lock, replace relevant list operations to rcu version and call synchronize_rcu() in unregister_break_hook().

And, replace write lock to spinlock in {un}register_break_hook.

Signed-off-by: Yang Shi yang.shi@linaro.org

Looks more plausible to me. Does it look OK to you, Steven?

Thanx, Paul

---

v2 -> v3 Add synchronize_rcu() in ungister_break_hook() Replace write lock to spinlock

v1 -> v2 Replace list operations to rcu version.

arch/arm64/kernel/debug-monitors.c | 21 +++++++++++---------- 1 file changed, 11 insertions(+), 10 deletions(-)

diff --git a/arch/arm64/kernel/debug-monitors.c b/arch/arm64/kernel/debug-monitors.c index cebf786..13ca9cd 100644 --- a/arch/arm64/kernel/debug-monitors.c +++ b/arch/arm64/kernel/debug-monitors.c @@ -271,20 +271,21 @@ static int single_step_handler(unsigned long addr, unsigned int esr,

• Use reader/writer locks instead of plain spinlock.

*/ static LIST_HEAD(break_hook); -static DEFINE_RWLOCK(break_hook_lock); +static DEFINE_SPINLOCK(break_hook_lock);

void register_break_hook(struct break_hook *hook) {

• write_lock(&break_hook_lock);
• list_add(&hook->node, &break_hook);
• write_unlock(&break_hook_lock);

• spin_lock(&break_hook_lock);
• list_add_rcu(&hook->node, &break_hook);
• spin_unlock(&break_hook_lock);

}

void unregister_break_hook(struct break_hook *hook) {

• write_lock(&break_hook_lock);
• list_del(&hook->node);
• write_unlock(&break_hook_lock);

• spin_lock(&break_hook_lock);
• list_del_rcu(&hook->node);
• spin_unlock(&break_hook_lock);
• synchronize_rcu();

}

static int call_break_hook(struct pt_regs *regs, unsigned int esr) @@ -292,11 +293,11 @@ static int call_break_hook(struct pt_regs *regs, unsigned int esr) struct break_hook *hook; int (*fn)(struct pt_regs *regs, unsigned int esr) = NULL;

• read_lock(&break_hook_lock);
• list_for_each_entry(hook, &break_hook, node)

• rcu_read_lock();
• list_for_each_entry_rcu(hook, &break_hook, node) if ((esr & hook->esr_mask) == hook->esr_val) fn = hook->fn;

• read_unlock(&break_hook_lock);

• rcu_read_unlock();

  return fn ? fn(regs, esr) : DBG_HOOK_ERROR;

}

2.0.2