Messages in this thread | | | Date | Thu, 01 Oct 2015 13:53:51 -0700 | From | "Shi, Yang" <> | Subject | Re: [v2 PATCH] arm64: replace read_lock to rcu lock in call_break_hook |
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On 10/1/2015 10:08 AM, Steven Rostedt wrote: > On Thu, 1 Oct 2015 09:37:37 -0700 > Yang Shi <yang.shi@linaro.org> 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 and replace relevant list operations to rcu >> version. >> >> Signed-off-by: Yang Shi <yang.shi@linaro.org> >> --- >> v1-> v2 >> Replace list operations to rcu version. >> >> arch/arm64/kernel/debug-monitors.c | 10 +++++----- >> 1 file changed, 5 insertions(+), 5 deletions(-) >> >> diff --git a/arch/arm64/kernel/debug-monitors.c b/arch/arm64/kernel/debug-monitors.c >> index cebf786..cf0e4fc 100644 >> --- a/arch/arm64/kernel/debug-monitors.c >> +++ b/arch/arm64/kernel/debug-monitors.c >> @@ -276,14 +276,14 @@ static DEFINE_RWLOCK(break_hook_lock); >> void register_break_hook(struct break_hook *hook) >> { >> write_lock(&break_hook_lock); >> - list_add(&hook->node, &break_hook); >> + list_add_rcu(&hook->node, &break_hook); >> write_unlock(&break_hook_lock); >> } >> >> void unregister_break_hook(struct break_hook *hook) >> { >> write_lock(&break_hook_lock); >> - list_del(&hook->node); >> + list_del_rcu(&hook->node); >> write_unlock(&break_hook_lock); >> } > > Shouldn't there be a synchronize_rcu() somewhere?
So far kgdb is the only user of unregister_break_hook in mainline kernel.
Just read Documentation/RCU/checklist.txt, it says:
Note that synchronize_rcu() -only- guarantees to wait until all currently executing rcu_read_lock()-protected RCU read-side critical sections complete.
For kgdb, the unregister is just called in kgdb_arch_exit by kgdb_unregister_io_module, which is called when rmmod kgdb module.
The break point handler is done synchronously. So, it sounds should be not a problem without calling synchronize_rcu().
Yang
> -- Steve > >> >> @@ -292,11 +292,11 @@ 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; >> } >
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