Messages in this thread | | | Date | Thu, 16 Apr 2009 15:15:07 -0400 | From | Vivek Goyal <> | Subject | Re: [PATCH] IO-Controller: Fix kernel panic after moving a task |
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On Thu, Apr 16, 2009 at 01:25:35PM +0800, Gui Jianfeng wrote: > Vivek Goyal wrote: > > +#ifdef CONFIG_IOSCHED_CFQ_HIER > > +static void changed_cgroup(struct io_context *ioc, struct cfq_io_context *cic) > > +{ > > + struct cfq_queue *async_cfqq = cic_to_cfqq(cic, 0); > > + struct cfq_queue *sync_cfqq = cic_to_cfqq(cic, 1); > > + struct cfq_data *cfqd = cic->key; > > + struct io_group *iog, *__iog; > > + unsigned long flags; > > + struct request_queue *q; > > + > > + if (unlikely(!cfqd)) > > + return; > > + > > + q = cfqd->q; > > + > > + spin_lock_irqsave(q->queue_lock, flags); > > + > > + iog = io_lookup_io_group_current(q); > > + > > Hi Vivek, > > I triggered another kernel panic when testing. When moving a task to another > cgroup, the corresponding iog may not be setup properly all the time. "iog" > might be NULL here. io_ioq_move() receives a NULL iog, kernel crash. > > Consider the following piece of code: > > 941 int elv_set_request(struct request_queue *q, struct request *rq, gfp_t gfp_mask) > 942 { > 943 struct elevator_queue *e = q->elevator; > 944 > 945 elv_fq_set_request_io_group(q, rq); > > -->task moving to a new group is happenning here. > > 946 > 947 /* > 948 * Optimization for noop, deadline and AS which maintain only single > 949 * ioq per io group > 950 */ > 951 if (elv_iosched_single_ioq(e)) > 952 return elv_fq_set_request_ioq(q, rq, gfp_mask); > 953 > 954 if (e->ops->elevator_set_req_fn) > 955 return e->ops->elevator_set_req_fn(q, rq, gfp_mask); > > cfq_set_request() will finally call io_ioq_move(), but the iog is NULL, beacause the iogs in the > hierarchy are not built yet. So kernel crashes. > > 956 > 957 rq->elevator_private = NULL; > 958 return 0; > 959 } >
Thanks Gui. Good catch.
> BUG: unable to handle kernel NULL pointer dereference at 000000bc > IP: [<c04ebf8f>] io_ioq_move+0xf2/0x109 > *pde = 6cc00067 > Oops: 0000 [#1] SMP > last sysfs file: /sys/block/hdb/queue/slice_idle > Modules linked in: ipv6 cpufreq_ondemand acpi_cpufreq dm_mirror dm_multipath sbs sbshc battery ac lp snd_hda_codec_realtek snd_hda_intel snd_hda_codec snd_seq_dummy snd_seq_oss snd_seq_midi_event snd_seq snd_seq_device snd_pcm_oss snd_mixer_oss snd_pcm serio_raw snd_timer rtc_cmos parport_pc snd r8169 button rtc_core parport soundcore mii i2c_i801 rtc_lib snd_page_alloc pcspkr i2c_core dm_region_hash dm_log dm_mod ext3 jbd mbcache uhci_hcd ohci_hcd ehci_hcd > > Pid: 5431, comm: dd Not tainted (2.6.29-rc7-vivek #19) Veriton M460 > EIP: 0060:[<c04ebf8f>] EFLAGS: 00010046 CPU: 0 > EIP is at io_ioq_move+0xf2/0x109 > EAX: f6203a88 EBX: f6792c94 ECX: f6203a84 EDX: 00000006 > ESI: 00000000 EDI: 00000000 EBP: f6203a60 ESP: f6304c28 > DS: 007b ES: 007b FS: 00d8 GS: 0033 SS: 0068 > Process dd (pid: 5431, ti=f6304000 task=f669dae0 task.ti=f6304000) > Stack: > f62478c0 0100dd40 f6247908 f62d995c 00000000 00000000 f675b54c c04e9182 > f638e9b0 00000282 f62d99a4 f6325a2c c04e9113 f5a707c0 c04e7ae0 f675b000 > f62d95fc f6325a2c c04e8501 00000010 f631e4e8 f675b000 00080000 ffffff10 > Call Trace: > [<c04e9182>] changed_cgroup+0x6f/0x8d > [<c04e9113>] changed_cgroup+0x0/0x8d > [<c04e7ae0>] __call_for_each_cic+0x1b/0x25 > [<c04e8501>] cfq_set_request+0x158/0x2c7 > [<c06316e6>] _spin_unlock_irqrestore+0x5/0x6 > [<c04eb106>] elv_fq_set_request_io_group+0x2b/0x3e > [<c04e83a9>] cfq_set_request+0x0/0x2c7 > [<c04dddcb>] elv_set_request+0x3e/0x4e > [<c04df3da>] get_request+0x1ed/0x29b > [<c04df9bb>] get_request_wait+0xdf/0xf2 > [<c04dfd89>] __make_request+0x2c6/0x372 > [<c049bd76>] do_mpage_readpage+0x4fe/0x5e3 > [<c04deba5>] generic_make_request+0x2d0/0x355 > [<c04dff47>] submit_bio+0x92/0x97 > [<c045bfcb>] add_to_page_cache_locked+0x8a/0xb7 > [<c049bfa4>] mpage_end_io_read+0x0/0x50 > [<c049b1b6>] mpage_bio_submit+0x19/0x1d > [<c049bf9a>] mpage_readpages+0x9b/0xa5 > [<f7dd18c7>] ext3_readpages+0x0/0x15 [ext3] > [<c0462192>] __do_page_cache_readahead+0xea/0x154 > [<f7dd2286>] ext3_get_block+0x0/0xbe [ext3] > [<c045d34d>] generic_file_aio_read+0x276/0x569 > [<c047cdd9>] do_sync_read+0xbf/0xfe > [<c043a3f2>] getnstimeofday+0x51/0xdb > [<c0434d3c>] autoremove_wake_function+0x0/0x2d > [<c041bdc3>] sched_slice+0x61/0x6a > [<c0423114>] task_tick_fair+0x3d/0x60 > [<c04c1d79>] security_file_permission+0xc/0xd > [<c047cd1a>] do_sync_read+0x0/0xfe > [<c047d35a>] vfs_read+0x6c/0x8b > [<c047d67e>] sys_read+0x3c/0x63 > [<c0402fc1>] sysenter_do_call+0x12/0x21 > [<c0630000>] schedule+0x551/0x830 > Code: 08 31 c9 89 da e8 77 fc ff ff 8b 86 bc 00 00 00 85 ff 89 43 38 8d 46 60 89 43 40 74 1d 83 c4 0c 89 d8 5b 5e 5f 5d e9 aa f9 ff ff <8b> 86 bc 00 00 00 89 43 38 8d 46 60 89 43 40 83 c4 0c 5b 5e 5f > EIP: [<c04ebf8f>] io_ioq_move+0xf2/0x109 SS:ESP 0068:f6304c28 > > Changelog: > > Make sure iogs in the hierarchy are built properly after moving a task to a new cgroup. > > Signed-off-by: Gui Jianfeng <guijianfeng@cn.fujitsu.com> > --- > block/cfq-iosched.c | 4 +++- > block/elevator-fq.c | 1 + > block/elevator-fq.h | 1 + > 3 files changed, 5 insertions(+), 1 deletions(-) > > diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c > index 0ecf7c7..6d7bb8a 100644 > --- a/block/cfq-iosched.c > +++ b/block/cfq-iosched.c > @@ -12,6 +12,8 @@ > #include <linux/rbtree.h> > #include <linux/ioprio.h> > #include <linux/blktrace_api.h> > +#include "elevator-fq.h" > +
I think above explicit inclusion of "elevator-fq.h" might be unnecessary as elevator.h includes elevator-fq.h and cfq-iosched.c is including elevator.h
> /* > * tunables > */ > @@ -1086,7 +1088,7 @@ static void changed_cgroup(struct io_context *ioc, struct cfq_io_context *cic) > > spin_lock_irqsave(q->queue_lock, flags); > > - iog = io_lookup_io_group_current(q); > + iog = io_get_io_group(q);
A one line comment here explaining the need to get_io_group instead of lookup_io_group will be nice.
Thanks Vivek
> > if (async_cfqq != NULL) { > __iog = cfqq_to_io_group(async_cfqq); > diff --git a/block/elevator-fq.c b/block/elevator-fq.c > index df53418..f81cf6a 100644 > --- a/block/elevator-fq.c > +++ b/block/elevator-fq.c > @@ -1191,6 +1191,7 @@ struct io_group *io_get_io_group(struct request_queue *q) > > return iog; > } > +EXPORT_SYMBOL(io_get_io_group); > > void io_free_root_group(struct elevator_queue *e) > { > diff --git a/block/elevator-fq.h b/block/elevator-fq.h > index fc4110d..f17e425 100644 > --- a/block/elevator-fq.h > +++ b/block/elevator-fq.h > @@ -459,6 +459,7 @@ static inline struct io_group *ioq_to_io_group(struct io_queue *ioq) > } > > #ifdef CONFIG_GROUP_IOSCHED > +extern struct io_group *io_get_io_group(struct request_queue *q); > extern int io_group_allow_merge(struct request *rq, struct bio *bio); > extern void io_ioq_move(struct elevator_queue *e, struct io_queue *ioq, > struct io_group *iog); > -- > 1.5.4.rc3 > >
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