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xen-devel
[Xen-devel] Re: [PATCH] blkfront: Move blkif_interrupt into a tasklet.
On Tue, Aug 16, 2011 at 04:26:54AM -0700, imammedo [via Xen] wrote:
>
> Jeremy Fitzhardinge wrote:
> >
> > Have you tried bisecting to see when this particular problem appeared?
> > It looks to me like something is accidentally re-enabling interrupts -
> > perhaps a stack overrun is corrupting the "flags" argument between a
> > spin_lock_irqsave()/restore pair.
> >
> > Is it only on 32-bit kernels?
> >
Any specific reason you did not include xen-devel in this email? I am
CC-ing it here.
> ------------[ cut here ]------------
> [604001.659925] WARNING: at block/blk-core.c:239 blk_start_queue+0x70/0x80()
> [604001.659964] Modules linked in: nfs lockd fscache auth_rpcgss nfs_acl
> sunrpc ip6t_REJECT nf_conntrack_ipv6 nf_conntrack_ipv4 nf_defrag_ipv4
> nf_defrag_ipv6 xt_state nf_conntrack ip6table_filter ip6_tables xen_netfront
> pcspkr [last unloaded: scsi_wait_scan]
> [604001.660147] Pid: 336, comm: udevd Tainted: G W 3.0.0+ #50
> [604001.660181] Call Trace:
> [604001.660209] [<c045c512>] warn_slowpath_common+0x72/0xa0
> [604001.660243] [<c06643a0>] ? blk_start_queue+0x70/0x80
> [604001.660275] [<c06643a0>] ? blk_start_queue+0x70/0x80
> [604001.660310] [<c045c562>] warn_slowpath_null+0x22/0x30
> [604001.660343] [<c06643a0>] blk_start_queue+0x70/0x80
> [604001.660379] [<c075e231>] kick_pending_request_queues+0x21/0x30
> [604001.660417] [<c075e42f>] blkif_interrupt+0x19f/0x2b0
> ...
> ------------[ cut here ]------------
>
> I've debugged a bit blk-core warning and can say:
> - Yes, It is 32-bit PAE kernel and happens only with it so far.
> - Affects PV xen guest, bare-metal and kvm configs are not affected.
> - Upstream kernel is affected as well.
> - Reproduces on xen 4.1.1 and 3.1.2 hosts
>
> IF flag is always restored at drivers/md/dm.c
> static void clone_endio(struct bio *bio, int error)
> ...
> dm_endio_fn endio = tio->ti->type->end_io;
> ...
> when page fault happens accessing tio->ti->type field.
>
> After successful resync with kernel's pagetable in
> do_page_fault->vmalloc_fault, io continues happily on, however with IF flag
> restored even if faulted context's eflags register had no IF flag set.
> It happens with random task every time.
>
> Here is ftrace call graph showing problematic place:
> ========================================================
> # tracer: function_graph
> #
> # function_graph latency trace v1.1.5 on 3.0.0+
> # --------------------------------------------------------------------
> # latency: 0 us, #42330/242738181, CPU#0 | (M:desktop VP:0, KP:0, SP:0 HP:0
> #P:1)
> # -----------------
> # | task: -0 (uid:0 nice:0 policy:0 rt_prio:0)
> # -----------------
> #
> # _-----=> irqs-off
> # / _----=> need-resched
> # | / _---=> hardirq/softirq
> # || / _--=> preempt-depth
> # ||| /
> # CPU|||| DURATION FUNCTION CALLS
> # | |||| | | | | | |
> 0) d... | xen_evtchn_do_upcall() {
> 0) d... | irq_enter() {
> 0) d.h. 2.880 us | }
> 0) d.h. | __xen_evtchn_do_upcall() {
> 0) d.h. 0.099 us | irq_to_desc();
> 0) d.h. | handle_edge_irq() {
> 0) d.h. 0.107 us | _raw_spin_lock();
> 0) d.h. | ack_dynirq() {
> 0) d.h. 3.153 us | }
> 0) d.h. | handle_irq_event() {
> 0) d.h. | handle_irq_event_percpu() {
> 0) d.h. | blkif_interrupt() {
> 0) d.h. 0.110 us | _raw_spin_lock_irqsave();
> 0) d.h. | __blk_end_request_all() {
> 0) d.h. |
> blk_update_bidi_request() {
> 0) d.h. | blk_update_request() {
> 0) d.h. | req_bio_endio() {
> 0) d.h. | bio_endio() {
> 0) d.h. | endio() {
> 0) d.h. | bio_put() {
> 0) d.h. 4.149 us | }
> 0) d.h. | dec_count() {
> 0) d.h. |
> mempool_free() {
> 0) d.h. 1.395 us | }
> 0) d.h. |
> read_callback() {
> 0) d.h. |
> bio_endio() {
> 0) d.h. |
> clone_endio() {
> 0) d.h. | /* ==>
> enter clone_endio: tio: c1e14c70 */
> 0) d.h. 0.104 us |
> arch_irqs_disabled_flags();
> 0) d.h. | /* ==>
> clone_endio: endio = tio->ti->type->end_io: tio->ti c918c040 */
> 0) d.h. 0.100 us |
> arch_irqs_disabled_flags();
> 0) d.h. 0.117 us |
> mirror_end_io();
> 0) d.h. |
> free_tio() {
> 0) d.h. 2.269 us | }
> 0) d.h. |
> bio_put() {
> 0) d.h. 3.933 us | }
> 0) d.h. |
> dec_pending() {
> 0) d.h. 0.100 us |
> atomic_dec_and_test();
> 0) d.h. |
> end_io_acct() {
> 0) d.h. 5.655 us | }
> 0) d.h. |
> free_io() {
> 0) d.h. 1.992 us | }
> 0) d.h. 0.098 us |
> trace_block_bio_complete();
> 0) d.h. |
> bio_endio() {
> 0) d.h. |
> clone_endio() {
> 0) d.h. |
> /* ==> enter clone_endio: tio: c1e14ee0 */
> 0) d.h. 0.098 us |
> arch_irqs_disabled_flags();
> 0) d.h. |
> do_page_fault() {
> 0) d.h. 0.103 us |
> xen_read_cr2();
> 0) d.h. |
> /* dpf: tsk: c785a6a0 mm: 0 comm: kworker/0:0 */
> 0) d.h. |
> /* before vmalloc_fault (c9552044) regs: c786db1c ip: c082bb20 eflags:
> 10002 err: 0 irq: off */
> ^^^ - fault error code
> 0) d.h. |
> vmalloc_fault() {
> 0) d.h. 0.104 us |
>
> xen_read_cr3();
> 0) d.h. |
>
> xen_pgd_val();
> 0) d.h. |
>
> xen_pgd_val();
> 0) d.h. |
>
> xen_set_pmd();
> 0) d.h. |
>
> xen_pmd_val();
> 0) d.h.+ 14.599 us |
> }
> 0) d.h.+ 18.019 us |
> }
> v -- irq enabled
> 0) ..h. |
> /* ==> clone_endio: endio = tio->ti->type->end_io: tio->ti c9552040 */
> 0) ..h. 0.102 us |
> arch_irqs_disabled_flags();
> 0) ..h. |
> /* <7>clone_endio BUG DETECTED irq */
> ========================================
>
> So IF flag is restored right after exiting from do_page_fault().
>
> Any thoughts why it might happen?
>
> PS:
> Full logs, additional trace patch, kernel config and a way reproduce bug can
> be found at https://bugzilla.redhat.com/show_bug.cgi?id=707552
>
>
>
> ______________________________________
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> below:
> http://xen.1045712.n5.nabble.com/Fix-the-occasional-xen-blkfront-deadlock-when-irqbalancing-tp2644296p4704111.html
> This email was sent by imammedo (via Nabble)
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