From mboxrd@z Thu Jan 1 00:00:00 1970 From: hannes.weisbach@mailbox.tu-dresden.de (Hannes Weisbach) Date: Thu, 23 Apr 2015 12:04:04 +0200 Subject: [lttng-dev] [BUG] lttng-sessiond Message-ID: <3E06425C-5C41-4BF7-8156-A62C4E9B5E60@mailbox.tu-dresden.de> Hello, I'm using LTTng with a kernel that has lock debugging enabled. I familiarized myself with LTTng using the "Hello world" example, where I encountered two bugs. 1) Using multiple probes for the lttng-sessiond arguments --kmod-probes and --extra-kmod-probes does not work: $ sudo lttng-sessiond --kmod-probes="hello,sched" -vvv [...] DEBUG1 - 11:54:22.413830 [17827/17827]: Modprobe successfully lttng-probe-sched (in modprobe_lttng() at modprobe.c:285) sh: 1: Syntax error: "(" unexpected DEBUG1 - 11:54:22.415273 [17827/17827]: Unable to load optional module (null); continuing (in modprobe_lttng() at modprobe.c:281) [...] $ sudo lttng-sessiond --kmod-probes="sched,hello" -vvv [...] DEBUG1 - 11:55:13.879976 [17896/17896]: Modprobe successfully lttng-probe-hello (in modprobe_lttng() at modprobe.c:285) sh: 1: Syntax error: "(" unexpected DEBUG1 - 11:55:13.881183 [17896/17896]: Unable to load optional module (null); continuing (in modprobe_lttng() at modprobe.c:281) [...] $ sudo lttng-sessiond --extra-kmod-probes="sched,hello" -vvv [...] DEBUG1 - 11:55:54.244515 [17966/17966]: Modprobe successfully lttng-probe-hello (in modprobe_lttng() at modprobe.c:285) sh: 1: Syntax error: "(" unexpected DEBUG1 - 11:55:54.245758 [17966/17966]: Unable to load optional module (null); continuing (in modprobe_lttng() at modprobe.c:281) [...] It seems, only the last argument (module) is loaded correctly. 2) Having lttng-sessiond started: $ sudo lttng-sessiond --kmod-probes=hello And the tracer configured: lttng create lttng enable-event hello_world -k 'lttng start' causes a locking failure to be reported: [ 159.783420] [ 159.783922] ===================================== [ 159.784067] [ BUG: bad unlock balance detected! ] [ 159.784067] 4.0.0-rc4-atlas+ #200 Tainted: G O [ 159.784067] ------------------------------------- [ 159.784067] lttng-sessiond/1441 is trying to release lock (sessions_mutex) at: [ 159.784067] [] mutex_unlock+0xe/0x10 [ 159.784067] but there are no more locks to release! [ 159.784067] [ 159.784067] other info that might help us debug this: [ 159.784067] no locks held by lttng-sessiond/1441. [ 159.784067] [ 159.784067] stack backtrace: [ 159.784067] CPU: 0 PID: 1441 Comm: lttng-sessiond Tainted: G O 4.0.0-rc4-atlas+ #200 [ 159.784067] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011 [ 159.784067] ffffffff81808c3e ffff88005d24fa28 ffffffff818029e0 0000000000000007 [ 159.784067] ffff880057c9cd60 ffff88005d24fa58 ffffffff810c1924 ffff88005d24fad8 [ 159.784067] ffff880057c9cd60 ffffffffa01ce070 ffffffff81808c3e ffff88005d24fa98 [ 159.784067] Call Trace: [ 159.784067] [] ? mutex_unlock+0xe/0x10 [ 159.784067] [] dump_stack+0x4c/0x65 [ 159.784067] [] print_unlock_imbalance_bug+0xf4/0x100 [ 159.784067] [] ? mutex_unlock+0xe/0x10 [ 159.784067] [] lock_release+0x2e6/0x460 [ 159.784067] [] __mutex_unlock_slowpath+0x76/0x190 [ 159.784067] [] mutex_unlock+0xe/0x10 [ 159.784067] [] lttng_session_enable+0x208/0x5b0 [lttng_tracer] [ 159.784067] [] lttng_session_ioctl+0x155/0x300 [lttng_tracer] [ 159.784067] [] ? __lock_acquire+0x570/0x1f60 [ 159.784067] [] ? sched_clock_local+0x25/0x90 [ 159.784067] [] ? do_wp_page+0x3a7/0x900 [ 159.784067] [] ? sched_clock_cpu+0x98/0xc0 [ 159.784067] [] ? local_clock+0x15/0x30 [ 159.784067] [] ? sched_clock_local+0x25/0x90 [ 159.784067] [] ? do_wp_page+0x3a7/0x900 [ 159.784067] [] ? __lock_acquire+0x570/0x1f60 [ 159.784067] [] ? do_wp_page+0x3a7/0x900 [ 159.784067] [] ? handle_mm_fault+0x310/0x18b0 [ 159.784067] [] ? sched_clock_local+0x25/0x90 [ 159.784067] [] ? sched_clock_local+0x25/0x90 [ 159.784067] [] ? __fget+0x111/0x260 [ 159.784067] [] ? sched_clock_cpu+0x98/0xc0 [ 159.784067] [] ? local_clock+0x15/0x30 [ 159.784067] [] ? __fget+0x111/0x260 [ 159.784067] [] do_vfs_ioctl+0x308/0x560 [ 159.784067] [] ? __fget+0x5/0x260 [ 159.784067] [] ? __do_page_fault+0x1f1/0x4c0 [ 159.784067] [] SyS_ioctl+0x81/0xa0 [ 159.784067] [] system_call_fastpath+0x16/0x1b I hope this helps. -- Best regards, Hannes -------------- next part -------------- A non-text attachment was scrubbed... Name: signature.asc Type: application/pgp-signature Size: 203 bytes Desc: Message signed with OpenPGP using GPGMail URL: