On Thu, Aug 28, 2025 at 9:25 AM Amir Goldstein <amir73il@xxxxxxxxx> wrote: > > On Thu, Aug 28, 2025 at 5:15 AM Gabriel Krisman Bertazi > <gabriel@xxxxxxxxxx> wrote: > > > > "NeilBrown" <neil@xxxxxxxxxx> writes: > > > > > On Thu, 28 Aug 2025, Amir Goldstein wrote: > > >> On Tue, Aug 26, 2025 at 9:01 PM André Almeida <andrealmeid@xxxxxxxxxx> wrote: > > >> > > > >> > > > >> > > > >> > Em 26/08/2025 04:31, Amir Goldstein escreveu: > > >> > > On Mon, Aug 25, 2025 at 3:31 PM André Almeida <andrealmeid@xxxxxxxxxx> wrote: > > >> > >> > > >> > >> Hi Amir, > > >> > >> > > >> > >> Em 22/08/2025 16:17, Amir Goldstein escreveu: > > >> > >> > > >> > >> [...] > > >> > >> > > >> > >> /* > > >> > >>>>>> - * Allow filesystems that are case-folding capable but deny composing > > >> > >>>>>> - * ovl stack from case-folded directories. > > >> > >>>>>> + * Exceptionally for layers with casefold, we accept that they have > > >> > >>>>>> + * their own hash and compare operations > > >> > >>>>>> */ > > >> > >>>>>> - if (sb_has_encoding(dentry->d_sb)) > > >> > >>>>>> - return IS_CASEFOLDED(d_inode(dentry)); > > >> > >>>>>> + if (ofs->casefold) > > >> > >>>>>> + return false; > > >> > >>>>> > > >> > >>>>> I think this is better as: > > >> > >>>>> if (sb_has_encoding(dentry->d_sb)) > > >> > >>>>> return false; > > >> > >>>>> > > >> > >>> > > >> > >>> And this still fails the test "Casefold enabled" for me. > > >> > >>> > > >> > >>> Maybe you are confused because this does not look like > > >> > >>> a test failure. It looks like this: > > >> > >>> > > >> > >>> generic/999 5s ... [19:10:21][ 150.667994] overlayfs: failed lookup > > >> > >>> in lower (ovl-lower/casefold, name='subdir', err=-116): parent wrong > > >> > >>> casefold > > >> > >>> [ 150.669741] overlayfs: failed lookup in lower (ovl-lower/casefold, > > >> > >>> name='subdir', err=-116): parent wrong casefold > > >> > >>> [ 150.760644] overlayfs: failed lookup in lower (/ovl-lower, > > >> > >>> name='casefold', err=-66): child wrong casefold > > >> > >>> [19:10:24] [not run] > > >> > >>> generic/999 -- overlayfs does not support casefold enabled layers > > >> > >>> Ran: generic/999 > > >> > >>> Not run: generic/999 > > >> > >>> Passed all 1 tests > > >> > >>> > > >> > >> > > >> > >> This is how the test output looks before my changes[1] to the test: > > >> > >> > > >> > >> $ ./run.sh > > >> > >> FSTYP -- ext4 > > >> > >> PLATFORM -- Linux/x86_64 archlinux 6.17.0-rc1+ #1174 SMP > > >> > >> PREEMPT_DYNAMIC Mon Aug 25 10:18:09 -03 2025 > > >> > >> MKFS_OPTIONS -- -F /dev/vdc > > >> > >> MOUNT_OPTIONS -- -o acl,user_xattr /dev/vdc /tmp/dir2 > > >> > >> > > >> > >> generic/999 1s ... [not run] overlayfs does not support casefold enabled > > >> > >> layers > > >> > >> Ran: generic/999 > > >> > >> Not run: generic/999 > > >> > >> Passed all 1 tests > > >> > >> > > >> > >> > > >> > >> And this is how it looks after my changes[1] to the test: > > >> > >> > > >> > >> $ ./run.sh > > >> > >> FSTYP -- ext4 > > >> > >> PLATFORM -- Linux/x86_64 archlinux 6.17.0-rc1+ #1174 SMP > > >> > >> PREEMPT_DYNAMIC Mon Aug 25 10:18:09 -03 2025 > > >> > >> MKFS_OPTIONS -- -F /dev/vdc > > >> > >> MOUNT_OPTIONS -- -o acl,user_xattr /dev/vdc /tmp/dir2 > > >> > >> > > >> > >> generic/999 1s > > >> > >> Ran: generic/999 > > >> > >> Passed all 1 tests > > >> > >> > > >> > >> So, as far as I can tell, the casefold enabled is not being skipped > > >> > >> after the fix to the test. > > >> > > > > >> > > Is this how it looks with your v6 or after fixing the bug: > > >> > > https://lore.kernel.org/linux-unionfs/68a8c4d7.050a0220.37038e.005c.GAE@xxxxxxxxxx/ > > >> > > > > >> > > Because for me this skipping started after fixing this bug > > >> > > Maybe we fixed the bug incorrectly, but I did not see what the problem > > >> > > was from a quick look. > > >> > > > > >> > > Can you test with my branch: > > >> > > https://github.com/amir73il/linux/commits/ovl_casefold/ > > >> > > > > >> > > > >> > Right, our branches have a different base, mine is older and based on > > >> > the tag vfs/vfs-6.18.mount. > > >> > > > >> > I have now tested with your branch, and indeed the test fails with > > >> > "overlayfs does not support casefold enabled". I did some debugging and > > >> > the missing commit from my branch that is making this difference here is > > >> > e8bd877fb76bb9f3 ("ovl: fix possible double unlink"). After reverting it > > >> > on top of your branch, the test works. I'm not sure yet why this > > >> > prevents the mount, but this is the call trace when the error happens: > > >> > > >> Wow, that is an interesting development race... > > >> > > >> > > > >> > TID/PID 860/860 (mount/mount): > > >> > > > >> > entry_SYSCALL_64_after_hwframe+0x77 > > >> > do_syscall_64+0xa2 > > >> > x64_sys_call+0x1bc3 > > >> > __x64_sys_fsconfig+0x46c > > >> > vfs_cmd_create+0x60 > > >> > vfs_get_tree+0x2e > > >> > ovl_get_tree+0x19 > > >> > get_tree_nodev+0x70 > > >> > ovl_fill_super+0x53b > > >> > ! 0us [-EINVAL] ovl_parent_lock > > >> > > > >> > And for the ovl_parent_lock() arguments, *parent="work", *child="#7". So > > >> > right now I'm trying to figure out why the dentry for #7 is not hashed. > > >> > > > >> > > >> The reason is this: > > >> > > >> static struct dentry *ext4_lookup(... > > >> { > > >> ... > > >> if (IS_ENABLED(CONFIG_UNICODE) && !inode && IS_CASEFOLDED(dir)) { > > >> /* Eventually we want to call d_add_ci(dentry, NULL) > > >> * for negative dentries in the encoding case as > > >> * well. For now, prevent the negative dentry > > >> * from being cached. > > >> */ > > >> return NULL; > > >> } > > >> > > >> return d_splice_alias(inode, dentry); > > >> } > > >> > > >> Neil, > > >> > > >> Apparently, the assumption that > > >> ovl_lookup_temp() => ovl_lookup_upper() => lookup_one() > > >> returns a hashed dentry is not always true. > > >> > > >> It may be always true for all the filesystems that are currently > > >> supported as an overlayfs > > >> upper layer fs (?), but it does not look like you can count on this > > >> for the wider vfs effort > > >> and we should try to come up with a solution for ovl_parent_lock() > > >> that will allow enabling > > >> casefolding on overlayfs layers. > > >> > > >> This patch seems to work. WDYT? > > >> > > >> Thanks, > > >> Amir. > > >> > > >> commit 5dfcd10378038637648f3f422e3d5097eb6faa5f > > >> Author: Amir Goldstein <amir73il@xxxxxxxxx> > > >> Date: Wed Aug 27 19:55:26 2025 +0200 > > >> > > >> ovl: adapt ovl_parent_lock() to casefolded directories > > >> > > >> e8bd877fb76bb9f3 ("ovl: fix possible double unlink") added a sanity > > >> check of !d_unhashed(child) to try to verify that child dentry was not > > >> unlinked while parent dir was unlocked. > > >> > > >> This "was not unlink" check has a false positive result in the case of > > >> casefolded parent dir, because in that case, ovl_create_temp() returns > > >> an unhashed dentry. > > >> > > >> Change the "was not unlinked" check to use cant_mount(child). > > >> cant_mount(child) means that child was unlinked while we have been > > >> holding a reference to child, so it could not have become negative. > > >> > > >> This fixes the error in ovl_parent_lock() in ovl_check_rename_whiteout() > > >> after ovl_create_temp() and allows mount of overlayfs with casefolding > > >> enabled layers. > > >> > > >> Reported-by: André Almeida <andrealmeid@xxxxxxxxxx> > > >> Link: https://lore.kernel.org/r/18704e8c-c734-43f3-bc7c-b8be345e1bf5@xxxxxxxxxx/ > > >> Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx> > > >> > > >> diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c > > >> index bec4a39d1b97c..bffbb59776720 100644 > > >> --- a/fs/overlayfs/util.c > > >> +++ b/fs/overlayfs/util.c > > >> @@ -1551,9 +1551,23 @@ void ovl_copyattr(struct inode *inode) > > >> > > >> int ovl_parent_lock(struct dentry *parent, struct dentry *child) > > >> { > > >> + bool is_unlinked; > > >> + > > >> inode_lock_nested(parent->d_inode, I_MUTEX_PARENT); > > >> - if (!child || > > >> - (!d_unhashed(child) && child->d_parent == parent)) > > >> + if (!child) > > >> + return 0; > > >> + > > >> + /* > > >> + * After re-acquiring parent dir lock, verify that child was not moved > > >> + * to another parent and that it was not unlinked. cant_mount() means > > >> + * that child was unlinked while parent was unlocked. Since we are > > >> + * holding a reference to child, it could not have become negative. > > >> + * d_unhashed(child) is not a strong enough indication for unlinked, > > >> + * because with casefolded parent dir, ovl_create_temp() returns an > > >> + * unhashed dentry. > > >> + */ > > >> + is_unlinked = cant_mount(child) || WARN_ON_ONCE(d_is_negative(child)); > > >> + if (!is_unlinked && child->d_parent == parent) > > >> return 0; > > >> > > >> inode_unlock(parent->d_inode); > > >> > > > > > > I don't feel comfortable with that. Letting ovl_parent_lock() succeed > > > on an unhashed dentry doesn't work for my longer term plans for locking. > > > I would really rather we got that dentry hashed. > > > > > > What is happening is : > > > - lookup on non-existent name -> unhashed dentry > > > - vfs_create on that dentry - still unhashed > > > - rename of that unhashed dentry -> confusion in ovl_parent_lock() > > > > > > If this were being done from user-space there would be another lookup > > > after the create and before the rename, and that would result in a > > > hashed dentry. > > > > > > Could ovl_create_real() do a lookup for the name if the dentry isn't > > > hashed? That should result in a dentry that can safely be passed to > > > ovl_parent_lock(). > > See patch below. Seems to get the job done. Thanks, Amir. > > FYI, if your future work for vfs assumes that fs will alway have the > dentry hashed after create, you may want to look at: > > static int ovl_instantiate(struct dentry *dentry, struct inode *inode, > ... > /* Force lookup of new upper hardlink to find its lower */ > if (hardlink) > d_drop(dentry); > > return 0; > } > > If your assumption is not true for overlayfs, it may not be true for other fs > as well. How could you verify that it is correct? > > I really hope that you have some opt-in strategy in mind, so those new > dirops assumptions would not have to include all possible filesystems. > commit 32786370148617766043f6d054ff40758ce79f21 (HEAD -> ovl_casefold) Author: Amir Goldstein <amir73il@xxxxxxxxx> Date: Wed Aug 27 19:55:26 2025 +0200 ovl: make sure that ovl_create_real() returns a hashed dentry e8bd877fb76bb9f3 ("ovl: fix possible double unlink") added a sanity check of !d_unhashed(child) to try to verify that child dentry was not unlinked while parent dir was unlocked. This "was not unlink" check has a false positive result in the case of casefolded parent dir, because in that case, ovl_create_temp() returns an unhashed dentry after ovl_create_real() gets an unhashed dentry from ovl_lookup_upper() and makes it positive. To avoid returning unhashed dentry from ovl_create_temp(), let ovl_create_real() lookup again after making the newdentry positive, so it always returns a hashed positive dentry (or an error). This fixes the error in ovl_parent_lock() in ovl_check_rename_whiteout() after ovl_create_temp() and allows mount of overlayfs with casefolding enabled layers. Reported-by: André Almeida <andrealmeid@xxxxxxxxxx> Closes: https://lore.kernel.org/r/18704e8c-c734-43f3-bc7c-b8be345e1bf5@xxxxxxxxxx/ Suggested-by: Neil Brown <neil@xxxxxxxxxx> Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx> diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c index 538a1b2dbb387..a5e9ddf3023b3 100644 --- a/fs/overlayfs/dir.c +++ b/fs/overlayfs/dir.c @@ -212,12 +212,32 @@ struct dentry *ovl_create_real(struct ovl_fs *ofs, struct dentry *parent, err = -EPERM; } } - if (!err && WARN_ON(!newdentry->d_inode)) { + if (err) + goto out; + + if (WARN_ON(!newdentry->d_inode)) { /* * Not quite sure if non-instantiated dentry is legal or not. * VFS doesn't seem to care so check and warn here. */ err = -EIO; + } else if (d_unhashed(newdentry)) { + struct dentry *d; + /* + * Some filesystems (i.e. casefolded) may return an unhashed + * negative dentry from the ovl_lookup_upper() call before + * ovl_create_real(). + * In that case, lookup again after making the newdentry + * positive, so ovl_create_upper() always returns a hashed + * positive dentry. + */ + d = ovl_lookup_upper(ofs, newdentry->d_name.name, parent, + newdentry->d_name.len); + dput(newdentry); + if (IS_ERR_OR_NULL(d)) + err = d ? PTR_ERR(d) : -ENOENT; + else + return d; } out: if (err) {
