On Thu, Feb 13, 2025 at 9:52 PM gaoxu <gaoxu2@xxxxxxxxx> wrote: > > > > > On Tue, Feb 11, 2025 at 7:14 PM gaoxu <gaoxu2@xxxxxxxxx> wrote: > > > > > > swp_swap_info() may return null; it is necessary to check the return > > > value to avoid NULL pointer dereference. The code for other calls to > > > swp_swap_info() includes checks, and __swap_duplicate() should also > > > include checks. > > > > > > The reason why swp_swap_info() returns NULL is unclear; it may be due > > > to CPU cache issues or DDR bit flips. The probability of this issue is > > > very small, and the stack info we encountered is as follows： > > > Unable to handle kernel NULL pointer dereference at virtual address > > > 0000000000000058 > > > [RB/E]rb_sreason_str_set: sreason_str set null_pointer Mem abort info: > > > ESR = 0x0000000096000005 > > > EC = 0x25: DABT (current EL), IL = 32 bits > > > SET = 0, FnV = 0 > > > EA = 0, S1PTW = 0 > > > FSC = 0x05: level 1 translation fault Data abort info: > > > ISV = 0, ISS = 0x00000005, ISS2 = 0x00000000 > > > CM = 0, WnR = 0, TnD = 0, TagAccess = 0 > > > GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0 user pgtable: 4k pages, > > > 39-bit VAs, pgdp=00000008a80e5000 [0000000000000058] > > > pgd=0000000000000000, p4d=0000000000000000, > > > pud=0000000000000000 > > > Internal error: Oops: 0000000096000005 [#1] PREEMPT SMP Skip md ftrace > > > buffer dump for: 0x1609e0 ... > > > pc : swap_duplicate+0x44/0x164 > > > lr : copy_page_range+0x508/0x1e78 > > > sp : ffffffc0f2a699e0 > > > x29: ffffffc0f2a699e0 x28: ffffff8a5b28d388 x27: ffffff8b06603388 > > > x26: ffffffdf7291fe70 x25: 0000000000000006 x24: 0000000000100073 > > > x23: 00000000002d2d2f x22: 0000000000000008 x21: 0000000000000000 > > > x20: 00000000002d2d2f x19: 18000000002d2d2f x18: ffffffdf726faec0 > > > x17: 0000000000000000 x16: 0010000000000001 x15: 0040000000000001 > > > x14: 0400000000000001 x13: ff7ffffffffffb7f x12: ffeffffffffffbff > > > x11: ffffff8a5c7e1898 x10: 0000000000000018 x9 : 0000000000000006 > > > x8 : 1800000000000000 x7 : 0000000000000000 x6 : ffffff8057c01f10 > > > x5 : 000000000000a318 x4 : 0000000000000000 x3 : 0000000000000000 > > > x2 : 0000006daf200000 x1 : 0000000000000001 x0 : 18000000002d2d2f Call > > > trace: > > > swap_duplicate+0x44/0x164 > > > copy_page_range+0x508/0x1e78 > > > copy_process+0x1278/0x21cc > > > kernel_clone+0x90/0x438 > > > __arm64_sys_clone+0x5c/0x8c > > > invoke_syscall+0x58/0x110 > > > do_el0_svc+0x8c/0xe0 > > > el0_svc+0x38/0x9c > > > el0t_64_sync_handler+0x44/0xec > > > el0t_64_sync+0x1a8/0x1ac > > > Code: 9139c35a 71006f3f 54000568 f8797b55 (f9402ea8) ---[ end trace > > > 0000000000000000 ]--- Kernel panic - not syncing: Oops: Fatal > > > exception > > > SMP: stopping secondary CPUs > > > > > > The patch seems to only provide a workaround, but there are no more > > > effective software solutions to handle the bit flips problem. This > > > path will change the issue from a system crash to a process exception, > > > thereby reducing the impact on the entire machine. > > > > > > Signed-off-by: gao xu <gaoxu2@xxxxxxxxx> > > > > Yeah this smells like a bug. A bit strange though - I have eyeballed the code, and > > we (should have?) locked the PTE before resolving it into the swap entry format. > > Which should have been enough to prevent the swap entry from being > > unmapped and freed up. Which should have been enough to prevent swapoff...? > > > > (are you even doing concurrent swapoff?) > No, the swapoff operation was not executed. > > > > Can you provide more context? What kernel version is this, what kind of > > workload is this, any reproducer, etc.? > kernel version is linux 6.6, Android15 - linux6.6.30. > > The issues encountered by mobile users during usage. > The system load should not be high, as there is no info related to low > memory found in the logs. > The probability of this issue occurring is very low and irregular. > We cannot reproduce the problem during stress testing in the laboratory. > > I found someone reporting a similar issue on the web, see: > https://lkml.indiana.edu/hypermail/linux/kernel/2406.0/02380.html > https://forum.proxmox.com/threads/get_swap_device-bad-swap-file-entry.155581/ > https://forums.unraid.net/topic/145497-server-crashes-with-repeated-get_swap_device-bad-swap-file-entry-3ffffffffffff/ It might be a non-swap entry mistakenly passed to swap functions. I remember fixing a similar issue in the Android Common Kernel 6.6: https://android.googlesource.com/kernel/common/+/119351fe20bc73b71c6 where a migration entry is mistakenly passed to swap APIs. In any case, we need to identify and fix the actual bug. > > > Thanks Barry
