On Sat, Feb 22, 2025 at 9:03 PM Kairui Song <ryncsn@xxxxxxxxx> wrote: > > On Sat, Feb 22, 2025 at 3:41 PM mawupeng <mawupeng1@xxxxxxxxxx> wrote: > > On 2025/2/22 15:33, Kairui Song wrote: > > > On Sat, Feb 22, 2025 at 10:56 AM Wupeng Ma <mawupeng1@xxxxxxxxxx> wrote: > > >> > > >> From: Ma Wupeng <mawupeng1@xxxxxxxxxx> > > >> > > >> During our test, infinite loop is produced during #PF will lead to infinite > > >> error log as follow: > > >> > > >> get_swap_device: Bad swap file entry 114000000 > > >> > > >> Digging into the source, we found that the swap entry is invalid due to > > >> unknown reason, and this lead to invalid swap_info_struct. Excessive log > > > > > > Hi Wupeng, > > > > > > What is the kernel version you are using? If it's another bug causing > > > this invalid swap entry, we should fix that bug instead, not > > > workaround it. > > > > > > This looks kind of similar to another PATCH & Bug report, corrupted > > > page table or swap entry: > > > https://lore.kernel.org/linux-mm/e223b0e6ba2f4924984b1917cc717bd5@xxxxxxxxx/ > > > > > > Might be the same kernel bug? Gaoxu mentioned the bug was observed on > > > Kernel 6.6.30 (android version), and neither of these two workarounds > > > will fix it completely, the invalid value could cause many other > > > issues too. We definitely need to find out the root cause. > > > > We are having this problem in linux-v5.10, since the log is lost and swap > > is not enabled in this machines, maybe memory corrupted in the pt. > > Thanks for the info, that's very strange. Since you didn't even enable > SWAP, it must be something else corrupted the page table I think > > > > > > >> printing can fill up the prioritized log space, leading to the purging of > > >> originally valid logs and hindering problem troubleshooting. To make this > > >> more robust, kill this task. > > >> > > >> Signed-off-by: Ma Wupeng <mawupeng1@xxxxxxxxxx> > > >> --- > > >> include/linux/swap.h | 1 + > > >> mm/memory.c | 9 ++++++++- > > >> mm/swapfile.c | 2 +- > > >> 3 files changed, 10 insertions(+), 2 deletions(-) > > >> > > >> diff --git a/include/linux/swap.h b/include/linux/swap.h > > >> index b13b72645db3..0fa39cf66bc4 100644 > > >> --- a/include/linux/swap.h > > >> +++ b/include/linux/swap.h > > >> @@ -508,6 +508,7 @@ struct backing_dev_info; > > >> extern int init_swap_address_space(unsigned int type, unsigned long nr_pages); > > >> extern void exit_swap_address_space(unsigned int type); > > >> extern struct swap_info_struct *get_swap_device(swp_entry_t entry); > > >> +struct swap_info_struct *_swap_info_get(swp_entry_t entry); > > >> sector_t swap_folio_sector(struct folio *folio); > > >> > > >> static inline void put_swap_device(struct swap_info_struct *si) > > >> diff --git a/mm/memory.c b/mm/memory.c > > >> index b4d3d4893267..2d36e5a644d1 100644 > > >> --- a/mm/memory.c > > >> +++ b/mm/memory.c > > >> @@ -4365,8 +4365,15 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) > > >> > > >> /* Prevent swapoff from happening to us. */ > > >> si = get_swap_device(entry); > > >> - if (unlikely(!si)) > > >> + if (unlikely(!si)) { > > >> + if (unlikely(!_swap_info_get(entry))) > > >> + /* > > >> + * return VM_FAULT_SIGBUS for invalid swap entry to > > >> + * avoid infinite #PF. > > >> + */ > > >> + ret = VM_FAULT_SIGBUS; > > > > > > This could lead to VM_FAULT_SIGBUS on swapoff. After swapoff > > > get_swap_device will return NULL. > > > > If swap is off, All swap pages should be swap in as expected, so > > such entry can not trigger do_swap_page? > > do_swap_page may get blocked due to some random reason, and then a > concurrent swapoff could swap in the entry and disable the device. > Very unlikely to trigger but in theory possible. The "goto out" in do_swap_page() should have handled this case. If swapoff occurred before the actual swap-in began, we should have aborted the swap-in, and userspace would retry. /* Prevent swapoff from happening to us. */ si = get_swap_device(entry); if (unlikely(!si)) goto out; Thanks Barry
