[BUG] Usersapce MTE error with allocation tag 0 when low on memory

[Catalin Marinas]

+ Steven Price who added the MTE swap support.

On Wed, Mar 29, 2023 at 02:55:49AM +0000, Qun-wei Lin (林群崴) wrote:
> Hi,
> 
> We meet the mass MTE errors happened in Android T with kernel-6.1.
> 
> When the system is under memory pressure, the MTE often triggers some
> error reporting in userspace.
> 
> Like the tombstone below, there are many reports with the acllocation
> tags of 0:
> 
> Build fingerprint:
> 'alps/vext_k6897v1_64/k6897v1_64:13/TP1A.220624.014/mp2ofp23:userdebug/
> dev-keys'
> Revision: '0'
> ABI: 'arm64'
> Timestamp: 2023-03-14 06:39:40.344251744+0800
> Process uptime: 0s
> Cmdline: /vendor/bin/hw/camerahalserver
> pid: 988, tid: 1395, name: binder:988_3  >>>
> /vendor/bin/hw/camerahalserver <<<
> uid: 1047
> tagged_addr_ctrl: 000000000007fff3 (PR_TAGGED_ADDR_ENABLE,
> PR_MTE_TCF_SYNC, mask 0xfffe)
> signal 11 (SIGSEGV), code 9 (SEGV_MTESERR), fault addr
> 0x0d000075f1d8d7f0
>     x0  00000075018d3fb0  x1  00000000c0306201  x2  00000075018d3ae8  x
> 3  000000000000720c
>     x4  0000000000000000  x5  0000000000000000  x6  00000642000004fe  x
> 7  0000054600000630
>     x8  00000000fffffff2  x9  b34a1094e7e33c3f  x10
> 00000075018d3a80  x11 00000075018d3a50
>     x12 ffffff80ffffffd0  x13 0000061e0000072c  x14
> 0000000000000004  x15 0000000000000000
>     x16 00000077f2dfcd78  x17 00000077da3a8ff0  x18
> 00000075011bc000  x19 0d000075f1d8d898
>     x20 0d000075f1d8d7f0  x21 0d000075f1d8d910  x22
> 0000000000000000  x23 00000000fffffff7
>     x24 00000075018d4000  x25 0000000000000000  x26
> 00000075018d3ff8  x27 00000000000fc000
>     x28 00000000000fe000  x29 00000075018d3b20
>     lr  00000077f2d9f164  sp  00000075018d3ad0  pc  00000077f2d9f134  p
> st 0000000080001000
> 
> backtrace:
>       #00 pc 000000000005d134  /system/lib64/libbinder.so
> (android::IPCThreadState::talkWithDriver(bool)+244) (BuildId:
> 8b5612259e4a42521c430456ec5939c7)
>       #01 pc 000000000005d448  /system/lib64/libbinder.so
> (android::IPCThreadState::getAndExecuteCommand()+24) (BuildId:
> 8b5612259e4a42521c430456ec5939c7)
>       #02 pc 000000000005dd64  /system/lib64/libbinder.so
> (android::IPCThreadState::joinThreadPool(bool)+68) (BuildId:
> 8b5612259e4a42521c430456ec5939c7)
>       #03 pc 000000000008dba8  /system/lib64/libbinder.so
> (android::PoolThread::threadLoop()+24) (BuildId:
> 8b5612259e4a42521c430456ec5939c7)
>       #04 pc 0000000000013440  /system/lib64/libutils.so
> (android::Thread::_threadLoop(void*)+416) (BuildId:
> 10aac5d4a671e4110bc00c9b69d83d8a)
>       #05 pc
> 00000000000c14cc  /apex/com.android.runtime/lib64/bionic/libc.so
> (__pthread_start(void*)+204) (BuildId:
> 718ecc04753b519b0f6289a7a2fcf117)
>       #06 pc
> 0000000000054930  /apex/com.android.runtime/lib64/bionic/libc.so
> (__start_thread+64) (BuildId: 718ecc04753b519b0f6289a7a2fcf117)
> 
> Memory tags around the fault address (0xd000075f1d8d7f0), one tag per
> 16 bytes:
>       0x75f1d8cf00: 0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0
>       0x75f1d8d000: 0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0
>       0x75f1d8d100: 0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0
>       0x75f1d8d200: 0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0
>       0x75f1d8d300: 0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0
>       0x75f1d8d400: 0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0
>       0x75f1d8d500: 0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0
>       0x75f1d8d600: 0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0
>     =>0x75f1d8d700: 0  0  0  0  0  0  0  0  0  0  0  0  0  0  0 [0]
>       0x75f1d8d800: 0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0
>       0x75f1d8d900: 0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0
>       0x75f1d8da00: 0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0
>       0x75f1d8db00: 0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0
>       0x75f1d8dc00: 0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0
>       0x75f1d8dd00: 0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0
>       0x75f1d8de00: 0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0
> 
> Also happens in coredump.
> 
> This problem only occurs when ZRAM is enabled, so we think there are
> some issues regarding swap in/out.
> 
> Having compared the differences between Kernel-5.15 and Kernel-6.1,
> We found the order of swap_free() and set_pte_at() is changed in
> do_swap_page().
> 
> When fault in, do_swap_page() will call swap_free() first:
> do_swap_page() -> swap_free() -> __swap_entry_free() ->
> free_swap_slot() -> swapcache_free_entries() -> swap_entry_free() ->
> swap_range_free() -> arch_swap_invalidate_page() ->
> mte_invalidate_tags_area() ->  mte_invalidate_tags() -> xa_erase()
> 
> and then call set_pte_at():
> do_swap_page() -> set_pte_at() -> __set_pte_at() -> mte_sync_tags() ->
> mte_sync_page_tags() -> mte_restore_tags() -> xa_load()
> 
> This means that the swap slot is invalidated before pte mapping, and
> this will cause the mte tag in XArray to be released before tag
> restore.
> 
> After I moved swap_free() to the next line of set_pte_at(), the problem
> is disappeared.
> 
> We suspect that the following patches, which have changed the order, do
> not consider the mte tag restoring in page fault flow:
> https://lore.kernel.org/all/20220131162940.210846-5-david@redhat.com/
> 
> Any suggestion is appreciated.
> 
> Thank you.