On Wed, Dec 04, 2013 at 09:06:39AM -0500, Tejun Heo wrote: > 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. > > This can be fixed by either giving sysfs_open_file->mutex different > lockdep keys depending on whether the file is regular or bin instead > of whether mmap exists or not, or avoiding grabbing > sysfs_open_file->mutex from sysfs_bin_mmap() if mmap is not actually > implemented. While the former is simpler for driver-core-linus, > driver-core-next already has SYSFS_FLAG_HAS_MMAP in place to implement > the latter and doesn't have inherent distinction between regular and > bin files. This patch implements the latter so that the fix is more > conducive to driver-core-next. > > Because anything beyond sysfs_open_file->sd can't be dereferenced > without locking the open file, cache whether mmap is implemented or > not in sysfs_open_file->sd->s_flags and update sysfs_bin_mmap() test > the flag and bail without grabbing the mutex if not implemented. > > Signed-off-by: Tejun Heo <t...@kernel.org> > Reported-by: Dave Jones <da...@redhat.com> > Tested-by: Dave Jones <da...@redhat.com> > Link: http://lkml.kernel.org/g/20131203184324.ga11...@redhat.com
Please forget about this. This is actually a lot harder to translate to kernfs. I'll prepare another patch. Sorry about the noise. Thanks. -- tejun -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/