On Wed, 12 Feb 2025 03:13:46 +0000 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. Actually very few of the swp_swap_info() callers check for a NULL return. > The reason why swp_swap_info() returns NULL is unclear; it may be due to > CPU cache issues or DDR bit flips. Quite possibly it's a kernel bug. > 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 > > ... > > --- a/mm/swapfile.c > +++ b/mm/swapfile.c > @@ -3521,6 +3521,8 @@ static int __swap_duplicate(swp_entry_t entry, unsigned char usage, int nr) > int err, i; > > si = swp_swap_info(entry); > + if (unlikely(!si)) > + return -EINVAL; > > offset = swp_offset(entry); > VM_WARN_ON(nr > SWAPFILE_CLUSTER - offset % SWAPFILE_CLUSTER); OK, I guess avoiding the crash is good. But please let's include a WARN so that we can perhaps fix the bug, if one is there.
