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. Thanks, Naoya Horiguchi
