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When running several kvm processes with lots of memory overcommitment, we have seen an oops during process shutdown: ------------[ cut here ]------------ Kernel BUG at 0000000000193434 [verbose debug info unavailable] addressing exception: 0005 [#1] PREEMPT SMP Modules linked in: kvm sunrpc qeth_l2 dm_mod qeth ccwgroup CPU: 10 Not tainted 2.6.28-rc4-kvm-bigiron-00521-g0ccca08-dirty #8 Process kuli (pid: 14460, task: 0000000149822338, ksp: 0000000024f57650) Krnl PSW : 0704e00180000000 0000000000193434 (unmap_vmas+0x884/0xf10) R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:0 AS:3 CC:2 PM:0 EA:3 Krnl GPRS: 0000000000000002 0000000000000000 000000051008d000 000003e05e6034e0 00000000001933f6 00000000000001e9 0000000407259e0a 00000002be88c400 00000200001c1000 0000000407259608 0000000407259e08 0000000024f577f0 0000000407259e09 0000000000445fa8 00000000001933f6 0000000024f577f0 Krnl Code: 0000000000193426: eb22000c000d sllg %r2,%r2,12 000000000019342c: a7180000 lhi %r1,0 0000000000193430: b2290012 iske %r1,%r2 >0000000000193434: a7110002 tmll %r1,2 0000000000193438: a7840006 brc 8,193444 000000000019343c: 9602c000 oi 0(%r12),2 0000000000193440: 96806000 oi 0(%r6),128 0000000000193444: a7110004 tmll %r1,4 Call Trace: ([<00000000001933f6>] unmap_vmas+0x846/0xf10) [<0000000000199680>] exit_mmap+0x210/0x458 [<000000000012a8f8>] mmput+0x54/0xfc [<000000000012f714>] exit_mm+0x134/0x144 [<000000000013120c>] do_exit+0x240/0x878 [<00000000001318dc>] do_group_exit+0x98/0xc8 [<000000000013e6b0>] get_signal_to_deliver+0x30c/0x358 [<000000000010bee0>] do_signal+0xec/0x860 [<0000000000112e30>] sysc_sigpending+0xe/0x22 [<000002000013198a>] 0x2000013198a INFO: lockdep is turned off. Last Breaking-Event-Address: [<00000000001a68d0>] free_swap_and_cache+0x1a0/0x1a4 <4>---[ end trace bc19f1d51ac9db7c ]--- The faulting instruction is the storage key operation (iske) in ptep_rcp_copy (called by pte_clear, called by unmap_vmas). iske reads dirty and reference bit information for a physical page and requires a valid physical address. Since we are in pte_clear, we cannot rely on the pte containing a valid address. Fortunately we dont need these information in pte_clear - after all there is no mapping. The best fix is to remove the needless call to ptep_rcp_copy that contains the iske. Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com> Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com> |
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