Messages in this thread Patch in this message | | | Date | Mon, 28 Sep 2009 18:06:49 +0900 | From | KAMEZAWA Hiroyuki <> | Subject | [BUGFIX][PATCH][rc1] memcg: fix refcnt goes to minus |
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> At testing my (small) patch, with high memory pressure to > memcg+hierarchy+softlimit, following is shown. > == > INFO: RCU detected CPU 0 stall (t=10000 jiffies) > sending NMI to all CPUs: > NMI backtrace for cpu 0 > CPU 0: > Modules linked in: sco bridge stp bnep l2cap crc16 bluetooth rfkill iptabl > e_filter ip_tables ip6table_filter ip6_tables x_tables ipv6 cpufreq_ondemand acpi_cpufreq dm_mirror dm_region_hash dm_log d > m_multipath dm_mod uinput ppdev i2c_i801 pcspkr i2c_core bnx2 sg e1000e parport_pc parport button shpchp megaraid_sas sd_mo > d scsi_mod ext3 jbd uhci_hcd ohci_hcd ehci_hcd [last unloaded: microcode] > Pid: 2886, comm: ruby Not tainted 2.6.31-mm1 #2 PRIMERGY > RIP: 0010:[<ffffffff810878fe>] [<ffffffff810878fe>] trace_hardirqs_off_ca > ller+0x3e/0xb RSP: 0018:ffff88004fa03d98 EFLAGS: 00000006 > RAX: 0000000000000046 RBX: 0000000000000c00 RCX: 000000000000e501 > RDX: ffff8806133564f0 RSI: 0000000000000002 RDI: ffffffff8102a940 > RBP: ffff88004fa03d98 R08: 0000000000000001 R09: 0000000000000000 > R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000002 > R13: 0000000000000046 R14: 00000000000000ff R15: ffff88004fa03f48 > FS: 00007fdeca0856f0(0000) GS:ffff88004fa00000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 00007fdeca09e000 CR3: 0000000619fc6000 CR4: 00000000000006f0 > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400 > Call Trace: > <#DB[1]> <<EOE>> Pid: 2886, comm: ruby Not tainted 2.6.31-mm1 #2 > Call Trace: > <NMI> [<ffffffff8100af79>] ? show_regs+0x49/0x50 > [<ffffffff81429385>] nmi_watchdog_tick+0x1e5/0x210 > [<ffffffff81428891>] do_nmi+0x1b1/0x2e0 > [<ffffffff8142808a>] nmi+0x1a/0x2c > [<ffffffff8102a940>] ? flat_send_IPI_mask+0x90/0xb0 > [<ffffffff810878fe>] ? trace_hardirqs_off_caller+0x3e/0xb0 > <<EOE>> <IRQ> [<ffffffff810884bd>] trace_hardirqs_off+0xd/0x10 > [<ffffffff8102a940>] flat_send_IPI_mask+0x90/0xb0 > [<ffffffff8102a9c9>] flat_send_IPI_all+0x69/0x70 > [<ffffffff81027372>] arch_trigger_all_cpu_backtrace+0x62/0xa0 > [<ffffffff810bff8e>] __rcu_pending+0x7e/0x370 > [<ffffffff810c02c7>] rcu_check_callbacks+0x47/0x130 > [<ffffffff81063a26>] update_process_times+0x46/0x70 > [<ffffffff81085930>] tick_sched_timer+0x60/0x160 > [<ffffffff810858d0>] ? tick_sched_timer+0x0/0x160 > [<ffffffff8107a03a>] __run_hrtimer+0xba/0x150 > [<ffffffff8107a325>] hrtimer_interrupt+0xd5/0x1b0 > [<ffffffff81426dfe>] ? trace_hardirqs_off_thunk+0x3a/0x3c > [<ffffffff8142cacd>] smp_apic_timer_interrupt+0x6d/0x9b > [<ffffffff8100cb33>] apic_timer_interrupt+0x13/0x20 > <EOI> [<ffffffff811317b6>] ? mem_cgroup_walk_tree+0x156/0x180 > [<ffffffff811316d3>] ? mem_cgroup_walk_tree+0x73/0x180 > [<ffffffff81131692>] ? mem_cgroup_walk_tree+0x32/0x180 > [<ffffffff81131a00>] ? mem_cgroup_get_local_stat+0x0/0x110 > [<ffffffff81131d5b>] ? mem_control_stat_show+0x14b/0x330 > [<ffffffff810a57fd>] ? cgroup_seqfile_show+0x3d/0x60 > [<ffffffff810a5b90>] ? cgroup_map_add+0x0/0x30 > [<ffffffff8115de03>] ? seq_read+0xf3/0x420 > [<ffffffff811d9926>] ? security_file_permission+0x16/0x20 > [<ffffffff8113b7ec>] ? vfs_read+0xcc/0x190 > [<ffffffff8113b9b5>] ? sys_read+0x55/0x90 > [<ffffffff8100bf9b>] ? system_call_fastpath+0x16/0x1b > ..... > ==
This is a patch for 2.6.31-rc1 (maybe no hunk with -mm) == __mem_cgroup_largest_soft_limit_node() returns a mem_cgroup_per_zone "mz" with incremnted mz->mem->css's refcnt. Then, the caller of this function has to call css_put(mz->mem->css).
But, mz can be !NULL even if "not found" i.e. without css_get(). By this, css->refcnt will go down to minus.
This may cause various things...one of results will be initite-loop in css_tryget() as this.
INFO: RCU detected CPU 0 stall (t=10000 jiffies) sending NMI to all CPUs: NMI backtrace for cpu 0 CPU 0: <snip>
<<EOE>> <IRQ> [<ffffffff810884bd>] trace_hardirqs_off+0xd/0x10 [<ffffffff8102a940>] flat_send_IPI_mask+0x90/0xb0 [<ffffffff8102a9c9>] flat_send_IPI_all+0x69/0x70 [<ffffffff81027372>] arch_trigger_all_cpu_backtrace+0x62/0xa0 [<ffffffff810bff8e>] __rcu_pending+0x7e/0x370 [<ffffffff810c02c7>] rcu_check_callbacks+0x47/0x130 [<ffffffff81063a26>] update_process_times+0x46/0x70 [<ffffffff81085930>] tick_sched_timer+0x60/0x160 [<ffffffff810858d0>] ? tick_sched_timer+0x0/0x160 [<ffffffff8107a03a>] __run_hrtimer+0xba/0x150 [<ffffffff8107a325>] hrtimer_interrupt+0xd5/0x1b0 [<ffffffff81426dfe>] ? trace_hardirqs_off_thunk+0x3a/0x3c [<ffffffff8142cacd>] smp_apic_timer_interrupt+0x6d/0x9b [<ffffffff8100cb33>] apic_timer_interrupt+0x13/0x20 <EOI> [<ffffffff811317b6>] ? mem_cgroup_walk_tree+0x156/0x180 [<ffffffff811316d3>] ? mem_cgroup_walk_tree+0x73/0x180 [<ffffffff81131692>] ? mem_cgroup_walk_tree+0x32/0x180 [<ffffffff81131a00>] ? mem_cgroup_get_local_stat+0x0/0x110 [<ffffffff81131d5b>] ? mem_control_stat_show+0x14b/0x330 [<ffffffff810a57fd>] ? cgroup_seqfile_show+0x3d/0x60
Above shows CPU0 caught in css_tryget()'s inifinite loop because of bad refcnt.
This is a fix to set mz=NULL at the top of retry path.
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
--- mm/memcontrol.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
Index: linux-2.6.32-rc1/mm/memcontrol.c =================================================================== --- linux-2.6.32-rc1.orig/mm/memcontrol.c +++ linux-2.6.32-rc1/mm/memcontrol.c @@ -447,9 +447,10 @@ static struct mem_cgroup_per_zone * __mem_cgroup_largest_soft_limit_node(struct mem_cgroup_tree_per_zone *mctz) { struct rb_node *rightmost = NULL; - struct mem_cgroup_per_zone *mz = NULL; + struct mem_cgroup_per_zone *mz; retry: + mz = NULL; rightmost = rb_last(&mctz->rb_root); if (!rightmost) goto done; /* Nothing to reclaim from */
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