https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=237470
Bug ID: 237470
Summary: [ppc][pseries] panic: Error evicting page: -7
Product: Base System
Version: CURRENT
Hardware: powerpc
OS: Any
Status: New
Severity: Affects Only Me
Priority: ---
Component: kern
Assignee: b...@freebsd.org
Reporter: lup...@freebsd.org
I have seen this issue happening a couple of times. It is difficult to
reproduce. In my case, it started happening more often when using a clang built
with debug info, to perform large parallel builds.
This is the panic message observed:
panic: Error evicting page: -7
cpuid = 10
time = 131979
KDB: stack backtrace:
0xe00033634910: at .kdb_backtrace+0x5c
0xe00033634a40: at .vpanic+0x1b4
0xe00033634b00: at .panic+0x38
0xe00033634b90: at .mphyp_pte_insert+0x304
0xe00033634cb0: at .moea64_pvo_enter+0x164
0xe00033634d40: at .moea64_enter+0x520
0xe00033634e40: at .moea64_enter_object+0xa8
0xe00033634ef0: at .pmap_enter_object+0xa8
0xe00033634fa0: at .vm_map_pmap_enter+0x2d0
0xe00033635070: at .vm_map_insert+0x550
0xe00033635170: at .vm_map_fixed+0x134
0xe00033635240: at .vm_mmap_object+0x484
0xe00033635350: at .vn_mmap+0x190
0xe00033635430: at .kern_mmap+0x474
0xe00033635550: at .sys_mmap+0x30
0xe000336355d0: at .trap+0x654
0xe00033635770: at .powerpc_interrupt+0x290
0xe00033635810: user SC trap by 0x81004e768: srr1=0x8000d032
r1=0x3fffb790 cr=0x22024024 xer=0 ctr=0x81004e940
r2=0x810075d80 frame=0xe00033635840
KDB: enter: panic
This seems to indicate that the PTE to be evicted was not found.
After some debugging, it seems to be that there is a race condition, between
mphyp_pte_unset() and mphyp_pte_insert(), that may cause the page chosen for
eviction to be removed by mphyp_pte_unset() before mphyp_pte_insert().
This can be explained as following:
- mphyp_pte_insert() locks the pvo to be inserted
- mphyp_pte_insert() obtains read access to mphyp_eviction_lock
- mphyp_pte_insert() tries to insert the corresponding pte but fails
- mphyp_pte_insert() releases mphyp_eviction_lock
- mphyp_pte_insert() acquires mphyp_eviction_lock for write
- mphyp_pte_insert() chooses a pte to evict - let's call it p
- mphyp_pte_unset(), on another thread, locks the pvo that corresponds to pte p
- mphyp_pte_unset() removes p (without holding mphyp_eviction_lock)
- mphyp_pte_insert() tries to remove p, but fails, because it was already
removed by another thread
- the system panics
KDB's acttrace on this panic supports the hypothesis above:
Tracing command clang-8 pid 44763 tid 100504 td 0xcf22 (CPU 10)
0xe00033634a40: at .vpanic+0x1d4
0xe00033634b00: at .panic+0x38
0xe00033634b90: at .mphyp_pte_insert+0x304
0xe00033634cb0: at .moea64_pvo_enter+0x164
0xe00033634d40: at .moea64_enter+0x520
0xe00033634e40: at .moea64_enter_object+0xa8
0xe00033634ef0: at .pmap_enter_object+0xa8
0xe00033634fa0: at .vm_map_pmap_enter+0x2d0
0xe00033635070: at .vm_map_insert+0x550
0xe00033635170: at .vm_map_fixed+0x134
0xe00033635240: at .vm_mmap_object+0x484
0xe00033635350: at .vn_mmap+0x190
0xe00033635430: at .kern_mmap+0x474
0xe00033635550: at .sys_mmap+0x30
0xe000336355d0: at .trap+0x654
0xe00033635770: at .powerpc_interrupt+0x290
0xe00033635810: user SC trap by 0x81004e768: srr1=0x8000d032
r1=0x3fffb790 cr=0x22024024 xer=0 ctr=0x81004e940
r2=0x810075d80 frame=0xe000336358
40
Tracing command clang-8 pid 44640 tid 100690 td 0xc0004913b000 (CPU 15)
0xe0003404fad0: at .intr_event_handle+0xf0
0xe0003404fb90: at .powerpc_dispatch_intr+0xf0
0xe0003404fc40: at .xicp_dispatch+0x274
0xe0003404fd00: at .powerpc_interrupt+0xc8
0xe0003404fda0: kernel EXI trap by .lock_delay+0x5c:
srr1=0x80009032
r1=0xe00034050050 cr=0x2000f084 xer=0 ctr=0x1b78
r2=0xc155e890 frame=0xe0003404fdd0
0xe00034050050: at 0xc000fa530c1c
0xe000340500e0: at .__mtx_lock_sleep+0x238
0xe000340501d0: at .__mtx_lock_flags+0x160
0xe00034050280: at .moea64_remove_pages+0x134
0xe00034050340: at .pmap_remove_pages+0x78
0xe000340503d0: at .vmspace_exit+0xf8
0xe00034050480: at .exit1+0x6d8
0xe00034050550: at .sys_sys_exit+0x1c
0xe000340505d0: at .trap+0x654
0xe00034050770: at .powerpc_interrupt+0x290
0xe00034050810: user SC trap by 0x8133eafd8: srr1=0x8000f032
r1=0x3fffd890 cr=0x22000242 xer=0x2000 ctr=0x8133eafd0
r2=0x8134bdbf0 frame=0xe00034050840
Process 44640 is exiting and removin
