diff options
authorTejun Heo <>2013-12-10 14:29:17 (GMT)
committerPawel Osmialowski <>2015-03-27 17:13:19 (GMT)
commit2fa66b1f180631e1908ea005328925d004b53c3c (patch)
parent08de0458716bb67d6db5d3046116694265427e35 (diff)
sysfs: bail early from kernfs_file_mmap() to avoid spurious lockdep warning
This is v3.14 fix for the same issue that a8b14744429f ("sysfs: give different locking key to regular and bin files") addresses for v3.13. Due to the extensive kernfs reorganization in v3.14 branch, the same fix couldn't be ported as-is. The v3.13 fix was ignored while merging it into v3.14 branch. 027a485d12e0 ("sysfs: use a separate locking class for open files depending on mmap") assigned different lockdep key to sysfs_open_file->mutex depending on whether the file implements mmap or not in an attempt to avoid spurious lockdep warning caused by merging of regular and bin file paths. While this restored some of the original behavior of using different locks (at least lockdep is concerned) for the different clases of files. The restoration wasn't full because now the lockdep key assignment depends on whether the file has mmap or not instead of whether it's a regular file or not. This means that bin files which don't implement mmap will get assigned the same lockdep class as regular files. This is problematic because file_operations for bin files still implements the mmap file operation and checking whether the sysfs file actually implements mmap happens in the file operation after grabbing @sysfs_open_file->mutex. We still end up adding locking dependency from mmap locking to sysfs_open_file->mutex to the regular file mutex which triggers spurious circular locking warning. For v3.13, a8b14744429f ("sysfs: give different locking key to regular and bin files") fixed it by giving sysfs_open_file->mutex different lockdep keys depending on whether the file is regular or bin instead of whether mmap exists or not; however, due to the way sysfs is now layered behind kernfs, this approach is no longer viable. kernfs can tell whether a sysfs node has mmap implemented or not but can't tell whether a bin file from a regular one. This patch updates kernfs such that kernfs_file_mmap() checks SYSFS_FLAG_HAS_MMAP and bail before grabbing sysfs_open_file->mutex so that it doesn't add spurious locking dependency from mmap to sysfs_open_file->mutex and changes sysfs so that it specifies kernfs_ops->mmap iff the sysfs file implements mmap. Combined, this ensures that sysfs_open_file->mutex is grabbed under mmap path iff the sysfs file actually implements mmap. As sysfs_open_file->mutex is already given a different lockdep key if mmap is implemented, this removes the spurious locking dependency. Signed-off-by: Tejun Heo <> Reported-by: Dave Jones <> Link: Signed-off-by: Greg Kroah-Hartman <>
2 files changed, 22 insertions, 8 deletions
diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c
index 990c97f..1e3cae6 100644
--- a/fs/kernfs/file.c
+++ b/fs/kernfs/file.c
@@ -422,6 +422,16 @@ static int kernfs_file_mmap(struct file *file, struct vm_area_struct *vma)
const struct kernfs_ops *ops;
int rc;
+ /*
+ * mmap path and of->mutex are prone to triggering spurious lockdep
+ * warnings and we don't want to add spurious locking dependency
+ * between the two. Check whether mmap is actually implemented
+ * without grabbing @of->mutex by testing HAS_MMAP flag. See the
+ * comment in kernfs_file_open() for more details.
+ */
+ if (!(of->sd->s_flags & SYSFS_FLAG_HAS_MMAP))
+ return -ENODEV;
rc = -ENODEV;
@@ -429,10 +439,7 @@ static int kernfs_file_mmap(struct file *file, struct vm_area_struct *vma)
goto out_unlock;
ops = kernfs_ops(of->sd);
- if (ops->mmap)
- rc = ops->mmap(of, vma);
- if (rc)
- goto out_put;
+ rc = ops->mmap(of, vma);
* PowerPC's pci_mmap of legacy_mem uses shmem_zero_setup()
@@ -597,6 +604,9 @@ static int kernfs_file_open(struct inode *inode, struct file *file)
* happen on the same file. At this point, we can't easily give
* each file a separate locking class. Let's differentiate on
* whether the file has mmap or not for now.
+ *
+ * Both paths of the branch look the same. They're supposed to
+ * look that way and give @of->mutex different static lockdep keys.
if (has_mmap)
diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
index ac77d2b..a67d1c6 100644
--- a/fs/sysfs/file.c
+++ b/fs/sysfs/file.c
@@ -142,9 +142,6 @@ static int sysfs_kf_bin_mmap(struct sysfs_open_file *of,
struct bin_attribute *battr = of->sd->priv;
struct kobject *kobj = of->sd->s_parent->priv;
- if (!battr->mmap)
- return -ENODEV;
return battr->mmap(of->file, kobj, battr, vma);
@@ -197,6 +194,11 @@ static const struct kernfs_ops sysfs_bin_kfops_wo = {
static const struct kernfs_ops sysfs_bin_kfops_rw = {
.read = sysfs_kf_bin_read,
.write = sysfs_kf_bin_write,
+static const struct kernfs_ops sysfs_bin_kfops_mmap = {
+ .read = sysfs_kf_bin_read,
+ .write = sysfs_kf_bin_write,
.mmap = sysfs_kf_bin_mmap,
@@ -232,7 +234,9 @@ int sysfs_add_file_mode_ns(struct sysfs_dirent *dir_sd,
} else {
struct bin_attribute *battr = (void *)attr;
- if ((battr->read && battr->write) || battr->mmap)
+ if (battr->mmap)
+ ops = &sysfs_bin_kfops_mmap;
+ else if (battr->read && battr->write)
ops = &sysfs_bin_kfops_rw;
else if (battr->read)
ops = &sysfs_bin_kfops_ro;