On Sun, Apr 25, 2021 at 9:14 AM Amir Goldstein <amir73il@xxxxxxxxx> wrote: > > Eryu, > > This extends the generic t_dir_offset2 helper program to verify > some cases of missing/stale entries and adds a new generic test which > passes on overlayfs (and other fs) on upstream kernel. > > The overlayfs specific test fails on upstream kernel and the fix commit > is currently in linux-next. As usual, you may want to wait with merging > until the fix commit hits upstream. > > Based on feedback from Miklos, I changed the test to check for the > missing/stale entries on a new fd, while old fd is kept open, because > POSIX allows for stale/missing entries in the old fd. > > I was looking into another speculated bug in overlayfs which involves > multiple calls to getdents. Although it turned out that overlayfs does > not have the speculated bug, I left both generic and overlay test with > multiple calls to getdents in order to excersize the relevant code. > > The attached patch was used to verify that the overlayfs test excercises > the call to ovl_cache_update_ino() with stale entries. > Overlayfs populates the merge dir readdir cache with a list of files in > the first getdents call, but updates d_ino of files on the list in > subsequent getdents calls. By that time, the last entry is stale and the > following warning is printed (on linux-next with patch below applied): > [ ] overlayfs: failed to look up (m100) for ino (0) > [ ] overlayfs: failed to look up (f100) for ino (0) > > Miklos, > > Do you think it is worth the trouble to set p->is_whiteout and skip > dir_emit() in this case? and do we need to worry about lookup_one_len() > returning -ENOENT in this case? So lookup_one_len() first does a cached lookup, and if found returns that. If not then it calls the filesystem's ->lookup() callback, which in this case is ovl_lookup(). AFAICS ovl_lookup() will never return ENOENT, even if the underlying filesystem does. Which means it's not necessary to worry about that case. The other case you found it that in case of a stale direntry the i_ino update will be skipped and so it will return an inconsistent result, right? Fixing that looks worthwhile, yes. Thanks, Miklos
