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?) Can you provide more context? What kernel version is this, what kind of workload is this, any reproducer, etc.?
