On 04/17, Chao Yu wrote: > On 2018/4/17 14:44, Chao Yu wrote: > > On 2018/4/17 4:16, Jaegeuk Kim wrote: > >> On 04/13, Chao Yu wrote: > >>> On 2018/4/13 12:05, Jaegeuk Kim wrote: > >>>> On 04/13, Chao Yu wrote: > >>>>> On 2018/4/13 9:04, Jaegeuk Kim wrote: > >>>>>> On 04/10, Chao Yu wrote: > >>>>>>> Hi Jaegeuk, > >>>>>>> > >>>>>>> On 2018/4/8 16:13, Chao Yu wrote: > >>>>>>>> f2fs doesn't allow abuse on atomic write class interface, so except > >>>>>>>> limiting in-mem pages' total memory usage capacity, we need to limit > >>>>>>>> start-commit time as well, otherwise we may run into infinite loop > >>>>>>>> during foreground GC because target blocks in victim segment are > >>>>>>>> belong to atomic opened file for long time. > >>>>>>>> > >>>>>>>> Now, we will check the condition with f2fs_balance_fs_bg in > >>>>>>>> background threads, once if user doesn't commit data exceeding 30 > >>>>>>>> seconds, we will drop all cached data, so I expect it can keep our > >>>>>>>> system running safely to prevent Dos attack. > >>>>>>> > >>>>>>> Is it worth to add this patch to avoid abuse on atomic write > >>>>>>> interface by user? > >>>>>> > >>>>>> Hmm, hope to see a real problem first in this case. > >>>>> > >>>>> I think this can be a more critical security leak instead of a > >>>>> potential issue > >>>>> which we can wait for someone reporting that can be too late. > >>>>> > >>>>> For example, user can simply write a huge file whose data spread in all > >>>>> f2fs > >>>>> segments, once user open that file as atomic, foreground GC will suffer > >>>>> deadloop, causing denying any further service of f2fs. > >>>> > >>>> How can you guarantee it won't happen within 30sec? If you want to avoid > >>>> that, > >>> > >>> Now the value is smaller than generic hang task threshold in order to > >>> avoid > >>> foreground GC helding gc_mutex too long, we can tune that parameter? > >>> > >>>> you have to take a look at foreground gc. > >>> > >>> What do you mean? let GC moves blocks of atomic write opened file? > >> > >> I thought that we first need to detect when foreground GC is stuck by such > >> the > >> huge number of atomic writes. Then, we need to do something like dropping > >> all > >> the atomic writes. > > > > Yup, that will be reasonable. :) > > If we drop all atomic writes, for those atomic write who act very normal, it > will case them losing all cached data without any hint like error return > value. > So should we just: > > - drop expired inmem pages. > - or set FI_DROP_ATOMIC flag, return -EIO during atomic_commit, and reset the > flag.
Like FI_ATOMIC_REVOKE_REQUEST in atomic_commit? > > Thanks, > > > > > Thanks, > > > >> > >>> > >>> Thanks, > >>> > >>>> > >>>>> > >>>>> Thanks, > >>>>> > >>>>>> > >>>>>>> Thanks, > >>>>>> > >>>>>> . > >>>>>> > >>>> > >>>> . > >>>> > >> > >> . > >> > > > > > > . > >
