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ovl: do not open/llseek lower file with upper sb_writers held 

overlayfs file open (ovl_maybe_lookup_lowerdata) and overlay file llseek
take the ovl_inode_lock, without holding upper sb_writers.

In case of nested lower overlay that uses same upper fs as this overlay,
lockdep will warn about (possibly false positive) circular lock
dependency when doing open/llseek of lower ovl file during copy up with
our upper sb_writers held, because the locking ordering seems reverse to
the locking order in ovl_copy_up_start():

- lower ovl_inode_lock
- upper sb_writers

Let the copy up "transaction" keeps an elevated mnt write count on upper
mnt, but leaves taking upper sb_writers to lower level helpers only when
they actually need it.  This allows to avoid holding upper sb_writers
during lower file open/llseek and prevents the lockdep warning.

Minimizing the scope of upper sb_writers during copy up is also needed
for fixing another possible deadlocks by a following patch.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
This commit is contained in:
Amir Goldstein 2023-08-16 12:42:18 +03:00
parent 162d064440
commit c63e56a4a6
2 changed files with 61 additions and 23 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

76
fs/overlayfs/copy_up.c
View File

@ -252,7 +252,9 @@ static int ovl_copy_up_file(struct ovl_fs *ofs, struct dentry *dentry,
return PTR_ERR(old_file);
/* Try to use clone_file_range to clone up within the same fs */
ovl_start_write(dentry);
cloned = do_clone_file_range(old_file, 0, new_file, 0, len, 0);
ovl_end_write(dentry);
if (cloned == len)
goto out_fput;
/* Couldn't clone, so now we try to copy the data */
@ -287,8 +289,12 @@ static int ovl_copy_up_file(struct ovl_fs *ofs, struct dentry *dentry,
* it may not recognize all kind of holes and sometimes
* only skips partial of hole area. However, it will be
* enough for most of the use cases.
*
* We do not hold upper sb_writers throughout the loop to avert
* lockdep warning with llseek of lower file in nested overlay:
* - upper sb_writers
* -- lower ovl_inode_lock (ovl_llseek)
*/
if (skip_hole && data_pos < old_pos) {
data_pos = vfs_llseek(old_file, old_pos, SEEK_DATA);
if (data_pos > old_pos) {
@ -303,9 +309,11 @@ static int ovl_copy_up_file(struct ovl_fs *ofs, struct dentry *dentry,
}
}
ovl_start_write(dentry);
bytes = do_splice_direct(old_file, &old_pos,
new_file, &new_pos,
this_len, SPLICE_F_MOVE);
ovl_end_write(dentry);
if (bytes <= 0) {
error = bytes;
break;
@ -555,14 +563,16 @@ static int ovl_link_up(struct ovl_copy_up_ctx *c)
struct ovl_fs *ofs = OVL_FS(c->dentry->d_sb);
struct inode *udir = d_inode(upperdir);
ovl_start_write(c->dentry);
/* Mark parent "impure" because it may now contain non-pure upper */
err = ovl_set_impure(c->parent, upperdir);
if (err)
return err;
goto out;
err = ovl_set_nlink_lower(c->dentry);
if (err)
return err;
goto out;
inode_lock_nested(udir, I_MUTEX_PARENT);
upper = ovl_lookup_upper(ofs, c->dentry->d_name.name, upperdir,
@ -581,10 +591,12 @@ static int ovl_link_up(struct ovl_copy_up_ctx *c)
}
inode_unlock(udir);
if (err)
return err;
goto out;
err = ovl_set_nlink_upper(c->dentry);
out:
ovl_end_write(c->dentry);
return err;
}
@ -719,21 +731,19 @@ static int ovl_copy_up_workdir(struct ovl_copy_up_ctx *c)
.link = c->link
};
/* workdir and destdir could be the same when copying up to indexdir */
err = -EIO;
if (lock_rename(c->workdir, c->destdir) != NULL)
goto unlock;
err = ovl_prep_cu_creds(c->dentry, &cc);
if (err)
goto unlock;
return err;
ovl_start_write(c->dentry);
inode_lock(wdir);
temp = ovl_create_temp(ofs, c->workdir, &cattr);
inode_unlock(wdir);
ovl_end_write(c->dentry);
ovl_revert_cu_creds(&cc);
err = PTR_ERR(temp);
if (IS_ERR(temp))
goto unlock;
return PTR_ERR(temp);
/*
* Copy up data first and then xattrs. Writing data after
@ -741,8 +751,21 @@ static int ovl_copy_up_workdir(struct ovl_copy_up_ctx *c)
*/
path.dentry = temp;
err = ovl_copy_up_data(c, &path);
if (err)
/*
* We cannot hold lock_rename() throughout this helper, because or
* lock ordering with sb_writers, which shouldn't be held when calling
* ovl_copy_up_data(), so lock workdir and destdir and make sure that
* temp wasn't moved before copy up completion or cleanup.
* If temp was moved, abort without the cleanup.
*/
ovl_start_write(c->dentry);
if (lock_rename(c->workdir, c->destdir) != NULL ||
temp->d_parent != c->workdir) {
err = -EIO;
goto unlock;
} else if (err) {
goto cleanup;
}
err = ovl_copy_up_metadata(c, temp);
if (err)
@ -779,6 +802,7 @@ static int ovl_copy_up_workdir(struct ovl_copy_up_ctx *c)
ovl_set_flag(OVL_WHITEOUTS, inode);
unlock:
unlock_rename(c->workdir, c->destdir);
ovl_end_write(c->dentry);
return err;
@ -802,9 +826,10 @@ static int ovl_copy_up_tmpfile(struct ovl_copy_up_ctx *c)
if (err)
return err;
ovl_start_write(c->dentry);
tmpfile = ovl_do_tmpfile(ofs, c->workdir, c->stat.mode);
ovl_end_write(c->dentry);
ovl_revert_cu_creds(&cc);
if (IS_ERR(tmpfile))
return PTR_ERR(tmpfile);
@ -815,9 +840,11 @@ static int ovl_copy_up_tmpfile(struct ovl_copy_up_ctx *c)
goto out_fput;
}
ovl_start_write(c->dentry);
err = ovl_copy_up_metadata(c, temp);
if (err)
goto out_fput;
goto out;
inode_lock_nested(udir, I_MUTEX_PARENT);
@ -831,7 +858,7 @@ static int ovl_copy_up_tmpfile(struct ovl_copy_up_ctx *c)
inode_unlock(udir);
if (err)
goto out_fput;
goto out;
if (c->metacopy_digest)
ovl_set_flag(OVL_HAS_DIGEST, d_inode(c->dentry));
@ -843,6 +870,8 @@ static int ovl_copy_up_tmpfile(struct ovl_copy_up_ctx *c)
ovl_set_upperdata(d_inode(c->dentry));
ovl_inode_update(d_inode(c->dentry), dget(temp));
out:
ovl_end_write(c->dentry);
out_fput:
fput(tmpfile);
return err;
@ -893,7 +922,9 @@ static int ovl_do_copy_up(struct ovl_copy_up_ctx *c)
* Mark parent "impure" because it may now contain non-pure
* upper
*/
ovl_start_write(c->dentry);
err = ovl_set_impure(c->parent, c->destdir);
ovl_end_write(c->dentry);
if (err)
return err;
}
@ -909,6 +940,7 @@ static int ovl_do_copy_up(struct ovl_copy_up_ctx *c)
if (c->indexed)
ovl_set_flag(OVL_INDEX, d_inode(c->dentry));
ovl_start_write(c->dentry);
if (to_index) {
/* Initialize nlink for copy up of disconnected dentry */
err = ovl_set_nlink_upper(c->dentry);
@ -923,6 +955,7 @@ static int ovl_do_copy_up(struct ovl_copy_up_ctx *c)
ovl_dentry_set_upper_alias(c->dentry);
ovl_dentry_update_reval(c->dentry, ovl_dentry_upper(c->dentry));
}
ovl_end_write(c->dentry);
out:
if (to_index)
@ -1011,15 +1044,16 @@ static int ovl_copy_up_meta_inode_data(struct ovl_copy_up_ctx *c)
* Writing to upper file will clear security.capability xattr. We
* don't want that to happen for normal copy-up operation.
*/
ovl_start_write(c->dentry);
if (capability) {
err = ovl_do_setxattr(ofs, upperpath.dentry, XATTR_NAME_CAPS,
capability, cap_size, 0);
if (err)
goto out_free;
}
err = ovl_removexattr(ofs, upperpath.dentry, OVL_XATTR_METACOPY);
if (!err) {
err = ovl_removexattr(ofs, upperpath.dentry,
OVL_XATTR_METACOPY);
}
ovl_end_write(c->dentry);
if (err)
goto out_free;

8
fs/overlayfs/util.c
View File

@ -670,6 +670,10 @@ bool ovl_already_copied_up(struct dentry *dentry, int flags)
return false;
}
/*
* The copy up "transaction" keeps an elevated mnt write count on upper mnt,
* but leaves taking freeze protection on upper sb to lower level helpers.
*/
int ovl_copy_up_start(struct dentry *dentry, int flags)
{
struct inode *inode = d_inode(dentry);
@ -682,7 +686,7 @@ int ovl_copy_up_start(struct dentry *dentry, int flags)
if (ovl_already_copied_up_locked(dentry, flags))
err = 1; /* Already copied up */
else
err = ovl_want_write(dentry);
err = ovl_get_write_access(dentry);
if (err)
goto out_unlock;
@ -695,7 +699,7 @@ out_unlock:
void ovl_copy_up_end(struct dentry *dentry)
{
ovl_drop_write(dentry);
ovl_put_write_access(dentry);
ovl_inode_unlock(d_inode(dentry));
}