On 2022/5/23 7:53, HORIGUCHI NAOYA(堀口 直也) wrote: > On Fri, May 20, 2022 at 04:17:45PM +0800, Miaohe Lin wrote: >> On 2022/5/20 14:34, HORIGUCHI NAOYA(堀口 直也) wrote: >>> On Thu, May 19, 2022 at 08:50:29PM +0800, Miaohe Lin wrote: >>>> When swap in shmem error at swapoff time, there would be a infinite loop >>>> in the while loop in shmem_unuse_inode(). It's because swapin error is >>>> deliberately ignored now and thus info->swapped will never reach 0. So >>>> we can't escape the loop in shmem_unuse(). >>>> >>>> In order to fix the issue, swapin_error entry is stored in the mapping >>>> when swapin error occurs. So the swapcache page can be freed and the >>>> user won't end up with a permanently mounted swap because a sector is >>>> bad. If the page is accessed later, the user process will be killed >>>> so that corrupted data is never consumed. On the other hand, if the >>>> page is never accessed, the user won't even notice it. >>>> >>>> Reported-by: Naoya Horiguchi <naoya.horiguchi@xxxxxxx> >>>> Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx> >>> >>> Hi Miaohe, >>> >>> Thank you for the update. I might miss something, but I still see the same >>> problem (I checked it on mm-everything-2022-05-19-00-03 + this patchset). >> >> I was testing this patch on my 5.10 kernel. I reproduced the problem in my env and >> fixed it. It seems there might be some critical difference though I checked that by >> reviewing the code... Sorry. :( >> >>> >>> This patch has the effect to change the return value of shmem_swapin_folio(), >>> -EIO (without this patch) to -EEXIST (with this patch). >> >> In fact, I didn't change the return value from -EIO to -EEXIST: >> >> @@ -1762,6 +1799,8 @@ static int shmem_swapin_folio(struct inode *inode, pgoff_t index, >> failed: >> if (!shmem_confirm_swap(mapping, index, swap)) >> error = -EEXIST; >> + if (error == -EIO) >> + shmem_set_folio_swapin_error(inode, index, folio, swap) >> >>> But shmem_unuse_swap_entries() checks neither, so no change from caller's view point. >>> Maybe breaking in errors (rather than ENOMEM) in for loop in shmem_unuse_swap_entries() >>> solves the issue? I briefly checked with the below change, then swapoff can return >>> with failure. >>> >>> @@ -1222,7 +1222,7 @@ static int shmem_unuse_swap_entries(struct inode *inode, >>> folio_put(folio); >>> ret++; >>> } >>> - if (error == -ENOMEM) >>> + if (error < 0) >>> break; >>> error = 0; >>> } >> >> Yes, this is the simplest and straightforward way to fix the issue. But it has the side effect >> that user will end up with a permanently mounted swap just because a sector is bad. That might >> be somewhat unacceptable? > > Ah, you're right, swapoff should return with success instead of with > failure. I tried the fix in your another email, and that makes swapoff > return with success, so your fix looks better than mine. I reproduced the deadloop issues when swapin error occurs at swapoff time in my linux-next-next-20220520 env, and I found this patch could solve the issue now with the fix in my another email. BTW: When I use dm-dust to inject the swapin IO error, I don't see non-uptodate folio when shmem_swapin_folio and swapoff succeeds. There might be some issues around that module (so I resort to the another way to inject the swapin error), but the patch itself works anyway. ;) > > Thanks, Thanks a lot! > Naoya Horiguchi >
