"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(). Might be a good time to mention I have a branch enabling negative dentries in casefolded directories. It didn't have any major issues last time I posted, but it didn't get much interest. It should be enough to resolve the unhashed dentries after a lookup due to casefolding. I'd need to revisit and retest, but it is a way out of it. -- Gabriel Krisman Bertazi
