fault injection caused oops in proc_flush_task

[Dave Jones <davej@redhat.com>]

Because I don't have enough oopses in my life, I decided to play
with the fault injection code today. It's not something I hear about
people trying too often, so I wondered what horrors lurk..

So I ran this..

#!/bin/bash

for FAILTYPE in failslab fail_page_alloc
do
 echo N > /sys/kernel/debug/$FAILTYPE/task-filter
 echo 50 > /sys/kernel/debug/$FAILTYPE/probability
 echo 500 > /sys/kernel/debug/$FAILTYPE/interval
 echo -1 > /sys/kernel/debug/$FAILTYPE/times
 echo 0 > /sys/kernel/debug/$FAILTYPE/space
 echo 0 > /sys/kernel/debug/$FAILTYPE/verbose
 echo 2 > /sys/kernel/debug/$FAILTYPE/ignore-gfp-wait
done

And then ran my usual fuzzing session, and saw this ..

Oops: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC
CPU: 2 PID: 8506 Comm: trinity-c124 Not tainted 3.16.0+ #41
task: ffff880227fc95e0 ti: ffff8800929a0000 task.ti: ffff8800929a0000
RIP: 0010:[<ffffffff8624a8f9>]  [<ffffffff8624a8f9>] proc_flush_task+0x99/0x1b0
RSP: 0018:ffff8800929a3d40  EFLAGS: 00010246
RAX: 0000000000000001 RBX: ffff8800929a3d6b RCX: 0000000000000000
RDX: ffff8800929a3d6c RSI: ffff8800929a3d58 RDI: 0000000000000000
RBP: ffff8800929a3da8 R08: 000000000000000a R09: 000000000000fffb
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000001
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000002
FS:  00007f019c95d700(0000) GS:ffff88024d100000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 00000000959e7000 CR4: 00000000001407e0
DR0: 000000000249e000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000600
Stack:
 ffff88022ad836c0 00000002929a3d58 ffff88022ad836c0 0000000132313068
 ffff8800929a3d6b 373231003277b6b0 ffff88022377b600 00000000898577d0
 ffff88022377b6b0 000000000000278f 0000000000000010 0000000000000000
Call Trace:
 [<ffffffff8607738c>] release_task+0x4c/0x4a0
 [<ffffffff86078aca>] wait_consider_task+0x70a/0xbe0
 [<ffffffff860790e4>] do_wait+0x144/0x2d0
 [<ffffffff8607967b>] SyS_wait4+0x7b/0x100
 [<ffffffff86077110>] ? task_stopped_code+0x60/0x60
 [<ffffffff8676371f>] tracesys+0xdd/0xe2
Code: d4 e0 a9 86 48 03 45 a8 89 4d a4 44 8b 78 30 48 8b 40 38 44 89 f9 4c 8b a8 40 08 00 00 31 c0 e8 6e 21 0f 00 48 8d 75 b0 89 45 b4 <49> 8b 7d 00 e8 4e 8b fa ff 48 85 c0 49 89 c6 74 18 48 89 c7 e8 
RIP  [<ffffffff8624a8f9>] proc_flush_task+0x99/0x1b0


Right before the oops, the last thing fault injection logged wrt that pid was..

FAULT_INJECTION: forcing a failure
CPU: 0 PID: 8506 Comm: trinity-c124 Not tainted 3.16.0+ #41
 0000000000000032 00000000898577d0 ffff8800929a3b08 ffffffff86759797
 ffffffff86c6a300 ffff8800929a3b28 ffffffff86358c30 0000000000008020
 0000000000008020 ffff8800929a3b38 ffffffff861c6850 ffff8800929a3b88
Call Trace:
 [<ffffffff86759797>] dump_stack+0x4e/0x7a
 [<ffffffff86358c30>] should_fail+0x100/0x110
 [<ffffffff861c6850>] should_failslab+0x40/0x50
 [<ffffffff861c32de>] kmem_cache_alloc+0x5e/0x270
 [<ffffffff86331e99>] ida_pre_get+0x69/0xf0
 [<ffffffff86245c80>] ? proc_fill_super+0xa0/0xa0
 [<ffffffff861da749>] get_anon_bdev+0x39/0x120
 [<ffffffff86245c80>] ? proc_fill_super+0xa0/0xa0
 [<ffffffff861da846>] set_anon_super+0x16/0x30
 [<ffffffff8624605d>] proc_set_super+0x1d/0x80
 [<ffffffff861db64a>] sget+0x33a/0x400
 [<ffffffff86246040>] ? proc_root_lookup+0x40/0x40
 [<ffffffff86245ed7>] proc_mount+0xa7/0x150
 [<ffffffff861dc338>] mount_fs+0x38/0x1c0
 [<ffffffff861f9574>] vfs_kern_mount+0x64/0x120
 [<ffffffff861f9649>] kern_mount_data+0x19/0x30
 [<ffffffff8624611c>] pid_ns_prepare_proc+0x1c/0x30
 [<ffffffff86094334>] alloc_pid+0x474/0x4c0
 [<ffffffff86047e10>] ? flush_tlb_mm_range+0x80/0x200
 [<ffffffff8600207d>] ? copy_thread+0x11d/0x2c0
 [<ffffffff86074140>] copy_process.part.29+0xab0/0x1be0
 [<ffffffff8607542d>] do_fork+0xdd/0x400
 [<ffffffff860a258b>] ? preempt_count_sub+0xab/0x100
 [<ffffffff8634b563>] ? __this_cpu_preempt_check+0x13/0x20
 [<ffffffff860757d6>] SyS_clone+0x16/0x20
 [<ffffffff86763869>] stub_clone+0x69/0x90
 [<ffffffff8676371f>] ? tracesys+0xdd/0xe2

Should proc_flush_task just be checking for a NULL upid->ns ?
Or is there something in the pid_ns_prepare_proc failure path
that we're failing to undo ?

thoughts?

I don't know how feasible it would be to hit that in real life
without the fault injection stuff, but an oops can't be the right
thing to do in any case.

	Dave