BUG_ON drivers/char/random.c:986 (Was: perf: use after free in perf_remove_from_context)

[Peter Zijlstra]

While fuzzing to reproduce my issue I hit the below, its triggered loads
of times and then the machine wedged (needed a power cycle), I can
provide the full console log if people care.

Anybody seen that one before?

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[  861.777414] ------------[ cut here ]------------
[  861.777416] kernel BUG at /usr/src/linux-2.6/drivers/char/random.c:986!
[  861.777419] invalid opcode: 0000 [#1] PREEMPT SMP 
[  861.777421] Modules linked in:
[  861.777424] CPU: 1 PID: 9851 Comm: trinity-c321 Not tainted 3.15.0-rc5-01700-g505011124ad0-dirty #1076
[  861.777425] Hardware name: Supermicro X8DTN/X8DTN, BIOS 4.6.3 01/08/2010
[  861.777426] task: ffff88022f68a600 ti: ffff88022f716000 task.ti: ffff88022f716000
[  861.777433] RIP: 0010:[<ffffffff81429ce4>]  [<ffffffff81429ce4>] account+0x164/0x170
[  861.777434] RSP: 0000:ffff88022f717e48  EFLAGS: 00010202
[  861.777435] RAX: ffffffff81c90788 RBX: 0000000000000991 RCX: 0000000000000000
[  861.777436] RDX: 0000000000000000 RSI: 0000000000000991 RDI: 0000000000002000
[  861.777437] RBP: ffff88022f717e70 R08: 0000000000000000 R09: 0000000000000000
[  861.777438] R10: 00000000000046c0 R11: 000000c8a18b27e1 R12: ffffffff81c90300
[  861.777439] R13: 0000000000000000 R14: ffffffff8142aff6 R15: ffffffff81a58605
[  861.777441] FS:  00007fba327ff700(0000) GS:ffff880237c20000(0000) knlGS:0000000000000000
[  861.777442] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  861.777443] CR2: 0000000000000010 CR3: 000000022f703000 CR4: 00000000000007e0
[  861.777444] Stack:
[  861.777446]  0000000000000991 0000000000007b44 0000000000000000 ffffffff8142aff6
[  861.777448]  ffffffff81a58605 ffff88022f717ed0 ffffffff8142ae82 0000000000000000
[  861.777450]  ffffffff81c90300 0000000000020000 ffff880233291240 ffff880435788690
[  861.777451] Call Trace:
[  861.777454]  [<ffffffff8142aff6>] ? urandom_read+0x46/0x120
[  861.777455]  [<ffffffff8142ae82>] extract_entropy_user+0x52/0x180
[  861.777457]  [<ffffffff8142aff6>] urandom_read+0x46/0x120
[  861.777462]  [<ffffffff811cdf3b>] vfs_read+0xab/0x180
[  861.777464]  [<ffffffff811ce1b2>] SyS_read+0x52/0xb0
[  861.777466]  [<ffffffff8168c939>] ia32_do_call+0x13/0x13
[  861.777489] Code: c9 81 e8 a0 5e cb ff ba 02 00 02 00 be 1d 00 00 00 48 c7 c7 c0 e5 c6 82 e8 9a 64 db ff 48 89 d8 5b 41 5c 41 5d 41 5e 41 5f 5d c3 <0f> 0b 66 2e 0f 1f 84 00 00 00 00 00 66 66 66 66 90 55 48 89 e5 
[  861.777491] RIP  [<ffffffff81429ce4>] account+0x164/0x170
[  861.777492]  RSP <ffff88022f717e48>
[  861.778140] ---[ end trace e70cc3dc70339c62 ]---
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