Messages in this thread | | | Date | Thu, 27 Oct 2011 10:00:16 +0200 | From | Ingo Molnar <> | Subject | Re: [GIT PULL rcu/next] RCU commits for 3.1 |
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* Paul E. McKenney <paulmck@linux.vnet.ibm.com> wrote:
> On Wed, Oct 26, 2011 at 10:30:20PM +0200, Ingo Molnar wrote: > > > > * Paul E. McKenney <paulmck@linux.vnet.ibm.com> wrote: > > > > > On Mon, Oct 24, 2011 at 03:05:01AM -0700, Paul E. McKenney wrote: > > > > On Tue, Oct 04, 2011 at 09:46:37AM +0200, Ingo Molnar wrote: > > > > > > > > > > * Paul E. McKenney <paulmck@linux.vnet.ibm.com> wrote: > > > > > > > > > > > On Mon, Oct 03, 2011 at 07:53:02AM +0200, Ingo Molnar wrote: > > > > > > > > > > > > > > Not sure whether you've seen this one already: > > > > > > > > > > > > This is a new one for me. > > > > > > > > > > > > > [ 18.110320] Adding 3911820k swap on /dev/sda2. Priority:-1 extents:1 across:3911820k > > > > > > > [ 31.803721] > > > > > > > [ 31.804597] =============================== > > > > > > > [ 31.804597] [ INFO: suspicious RCU usage. ] > > > > > > > [ 31.804597] ------------------------------- > > > > > > > [ 31.804597] include/linux/cgroup.h:548 suspicious rcu_dereference_check() usage! > > > > > > > [ 31.804597] > > > > > > > [ 31.804597] other info that might help us debug this: > > > > > > > [ 31.804597] > > > > > > > [ 31.804597] > > > > > > > [ 31.804597] rcu_scheduler_active = 1, debug_locks = 0 > > > > > > > [ 31.804597] 1 lock held by true/845: > > > > > > > [ 31.804597] #0: (&sig->cred_guard_mutex){+.+.+.}, at: [<4109f06f>] prepare_bprm_creds+0x20/0x55 > > > > > > > [ 31.804597] > > > > > > > [ 31.804597] stack backtrace: > > > > > > > [ 31.804597] Pid: 845, comm: true Not tainted 3.1.0-rc8-tip-01699-gde204a2-dirty #157471 > > > > > > > [ 31.804597] Call Trace: > > > > > > > [ 31.804597] [<412d78fa>] ? printk+0x18/0x1a > > > > > > > [ 31.804597] [<41044190>] lockdep_rcu_suspicious+0xb1/0xb9 > > > > > > > [ 31.804597] [<4106d6de>] perf_event_comm+0xb1/0x357 > > > > > > > [ 31.804597] [<4109f048>] set_task_comm+0x4d/0x54 > > > > > > > > > > > > This one does task_lock(), which acquires the task's > > > > > > ->alloc lock. In theory, this should prevent the > > > > > > lockdep-RCU splat. It clearly does not, and here are > > > > > > some possible reasons why: > > > > > > > > > > > > 1. Something redirects to some other task along the way. > > > > > > > > > > > > 2. Something releases ->alloc_lock along the way. > > > > > > > > > > > > The output above shows no locks held, which points to #2. > > > > > > > > > > > > set_task_comm() calls perf_event_comm() shown above, which calls > > > > > > perf_event_comm_event(), which does rcu_read_lock(), which should > > > > > > also prevent the splat. Then perf_event_comm_event() calls > > > > > > perf_event_comm_ctx(), which calls perf_event_comm_output()... > > > > > > > > > > > > Holy inlining, Batman!!! > > > > > > > > > > > > OK, I confess, I am a wuss... Any chance of reproducing this > > > > > > with CONFIG_SCHED_OMIT_FRAME_POINTER=n? Or would someone more > > > > > > familiar with these functions be willing to enlighten me? > > > > > > > > > > Ok, i ran the tests some more and here's a similar splat with > > > > > framepointers enabled: > > > > > > > > > > [ 50.402719] eth0: no IPv6 routers present > > > > > [ 59.147572] > > > > > [ 59.149064] =============================== > > > > > [ 59.151257] [ INFO: suspicious RCU usage. ] > > > > > [ 59.156865] ------------------------------- > > > > > [ 59.156865] include/linux/cgroup.h:548 suspicious rcu_dereference_check() usage! > > > > > [ 59.156865] > > > > > [ 59.156865] other info that might help us debug this: > > > > > [ 59.156865] > > > > > [ 59.156865] > > > > > [ 59.156865] rcu_scheduler_active = 1, debug_locks = 0 > > > > > [ 59.156865] 1 lock held by true/667: > > > > > [ 59.156865] #0: (&sig->cred_guard_mutex){+.+.+.}, at: [<c111d927>] prepare_bprm_creds+0x27/0x70 > > > > > [ 59.156865] > > > > > [ 59.156865] stack backtrace: > > > > > [ 59.156865] Pid: 667, comm: true Not tainted 3.1.0-rc8-tip+ #157499 > > > > > [ 59.156865] Call Trace: > > > > > [ 59.156865] [<c1a41f7c>] ? printk+0x28/0x2a > > > > > [ 59.156865] [<c109d540>] lockdep_rcu_suspicious+0xc0/0xd0 > > > > > [ 59.156865] [<c10d8a98>] perf_event_enable_on_exec+0x1c8/0x1d0 > > > > > [ 59.156865] [<c109c364>] ? __lock_release+0x54/0xd0 > > > > > [ 59.156865] [<c10daef8>] perf_event_comm+0x18/0x60 > > > > > [ 59.156865] [<c111d80d>] ? set_task_comm+0x5d/0x80 > > > > > [ 59.156865] [<c1a6ac6d>] ? _raw_spin_unlock+0x1d/0x30 > > > > > [ 59.156865] [<c111d814>] set_task_comm+0x64/0x80 > > > > > [ 59.156865] [<c111e355>] setup_new_exec+0xc5/0x1f0 > > > > > [ 59.156865] [<c115313b>] load_elf_binary+0x28b/0xa00 > > > > > [ 59.156865] [<c111de59>] ? search_binary_handler+0xd9/0x1d0 > > > > > [ 59.156865] [<c109c364>] ? __lock_release+0x54/0xd0 > > > > > [ 59.156865] [<c1152eb0>] ? do_mmap+0x60/0x60 > > > > > [ 59.156865] [<c111de60>] search_binary_handler+0xe0/0x1d0 > > > > > [ 59.156865] [<c111ddb0>] ? search_binary_handler+0x30/0x1d0 > > > > > [ 59.156865] [<c111e17f>] do_execve_common+0x22f/0x2a0 > > > > > [ 59.156865] [<c111e202>] do_execve+0x12/0x20 > > > > > [ 59.156865] [<c1036462>] sys_execve+0x32/0x70 > > > > > [ 59.156865] [<c1a6c052>] ptregs_execve+0x12/0x18 > > > > > [ 59.156865] [<c1a6bfd7>] ? sysenter_do_call+0x12/0x36 > > > > > > > > > > Config and full bootlog attached. > > > > > > > > Hello, Ingo, > > > > > > > > It appears that inlining has defeated me, so I tried reproducing under > > > > KVM, using the closest bootable approximation to your .config (attached). > > > > I booted ten times without seeing this error. I have my changes against > > > > 3.1-rc8. I will try against 3.1, but in the meantime any enlightenment > > > > would be most welcome. ;-) > > > > > > And I cannot reproduce after merging into 3.1. :-( > > > > Here's another one i just got with latest -tip: > > > > PM: Adding info for No Bus:vcsa2 > > > > =============================== > > [ INFO: suspicious RCU usage. ] > > ------------------------------- > > include/linux/cgroup.h:548 suspicious rcu_dereference_check() usage! > > > > other info that might help us debug this: > > > > > > rcu_scheduler_active = 1, debug_locks = 0 > > 1 lock held by true/655: > > #0: (&sig->cred_guard_mutex){+.+.+.}, at: [<810d1bd7>] prepare_bprm_creds+0x27/0x70 > > > > stack backtrace: > > Pid: 655, comm: true Not tainted 3.1.0-tip-01868-g1271bd2-dirty #161079 > > Call Trace: > > [<81abe239>] ? printk+0x18/0x1a > > [<81064920>] lockdep_rcu_suspicious+0xc0/0xd0 > > [<8108aa02>] perf_event_enable_on_exec+0x1d2/0x1e0 > > [<81063764>] ? __lock_release+0x54/0xb0 > > [<8108cca8>] perf_event_comm+0x18/0x60 > > [<810d1abd>] ? set_task_comm+0x5d/0x80 > > [<81af622d>] ? _raw_spin_unlock+0x1d/0x40 > > [<810d1ac4>] set_task_comm+0x64/0x80 > > [<810d25fd>] setup_new_exec+0xbd/0x1d0 > > [<810d1b61>] ? flush_old_exec+0x81/0xa0 > > [<8110753e>] load_elf_binary+0x28e/0xa00 > > [<810d2101>] ? search_binary_handler+0xd1/0x1d0 > > [<81063764>] ? __lock_release+0x54/0xb0 > > [<811072b0>] ? load_elf_library+0x260/0x260 > > [<810d2108>] search_binary_handler+0xd8/0x1d0 > > [<810d2060>] ? search_binary_handler+0x30/0x1d0 > > [<810d242f>] do_execve_common+0x22f/0x2a0 > > [<810d24b2>] do_execve+0x12/0x20 > > [<81009592>] sys_execve+0x32/0x70 > > [<81af7752>] ptregs_execve+0x12/0x20 > > [<81af76d4>] ? sysenter_do_call+0x12/0x36 > > > > Note that the backtrace suggests that perf was used - and indeed on > > that testbox i have this in rc.local: > > > > /home/mingo/bin/perf stat true & > > > > ... which i forgot about, completely. > > > > If you try 'perf stat true' can you trigger the warning perhaps? > > Ah! I will install this into my KVM image and see what happens. > Your /home/mingo/bin/perf is a script that does "perf stat true" > in a loop?
no, it's just plain 'perf' installed locally.
Thanks,
Ingo
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