* [PATCH] kernfs: fix locking around kernfs_ops->release() callback [not found] ` <20170211044855.GC3897@atomide.com> @ 2017-02-11 20:33 ` Tejun Heo 2017-02-13 17:57 ` Tony Lindgren 2017-02-21 20:50 ` Tejun Heo 0 siblings, 2 replies; 4+ messages in thread From: Tejun Heo @ 2017-02-11 20:33 UTC (permalink / raw) To: linux-kernel, Greg Kroah-Hartman; +Cc: Tony Lindgren The release callback may be called from two places - file release operation and kernfs open file draining. kernfs_open_file->mutex is used to synchronize the two callsites. This unfortunately leads to possible circular locking because of->mutex is used to protect the usual kernfs operations which may use locking constructs which are held while removing and thus draining kernfs files. @of->mutex is for synchronizing concurrent kernfs access operations and all we need here is synchronization between the releaes and drain paths. As the drain path has to grab kernfs_open_file_mutex anyway, let's use the mutex to synchronize the release operation instead. Signed-off-by: Tejun Heo <tj@kernel.org> Reported-by: Tony Lindgren <tony@atomide.com> Fixes: 0e67db2f9fe9 ("kernfs: add kernfs_ops->open/release() callbacks") --- Hello, Tony, can you please verify that this resolves the lockdep warnings that you've been seeing on linux-next? Greg, this is a fix for the kernfs patches which are being routed through the cgroup tree. Once Tony confirms, I'll apply this patch on top. Thanks! fs/kernfs/file.c | 19 ++++++++++++++----- 1 file changed, 14 insertions(+), 5 deletions(-) --- a/fs/kernfs/file.c +++ b/fs/kernfs/file.c @@ -747,10 +747,15 @@ err_out: static void kernfs_release_file(struct kernfs_node *kn, struct kernfs_open_file *of) { - if (!(kn->flags & KERNFS_HAS_RELEASE)) - return; + /* + * @of is guaranteed to have no other file operations in flight and + * we just want to synchronize release and drain paths. + * @kernfs_open_file_mutex is enough. @of->mutex can't be used + * here because drain path may be called from places which can + * cause circular dependency. + */ + lockdep_assert_held(&kernfs_open_file_mutex); - mutex_lock(&of->mutex); if (!of->released) { /* * A file is never detached without being released and we @@ -760,7 +765,6 @@ static void kernfs_release_file(struct k kn->attr.ops->release(of); of->released = true; } - mutex_unlock(&of->mutex); } static int kernfs_fop_release(struct inode *inode, struct file *filp) @@ -768,7 +772,12 @@ static int kernfs_fop_release(struct ino struct kernfs_node *kn = filp->f_path.dentry->d_fsdata; struct kernfs_open_file *of = kernfs_of(filp); - kernfs_release_file(kn, of); + if (kn->flags & KERNFS_HAS_RELEASE) { + mutex_lock(&kernfs_open_file_mutex); + kernfs_release_file(kn, of); + mutex_unlock(&kernfs_open_file_mutex); + } + kernfs_put_open_node(kn, of); seq_release(inode, filp); kfree(of->prealloc_buf); ^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] kernfs: fix locking around kernfs_ops->release() callback 2017-02-11 20:33 ` [PATCH] kernfs: fix locking around kernfs_ops->release() callback Tejun Heo @ 2017-02-13 17:57 ` Tony Lindgren 2017-02-13 18:22 ` Greg Kroah-Hartman 2017-02-21 20:50 ` Tejun Heo 1 sibling, 1 reply; 4+ messages in thread From: Tony Lindgren @ 2017-02-13 17:57 UTC (permalink / raw) To: Tejun Heo; +Cc: linux-kernel, Greg Kroah-Hartman * Tejun Heo <tj@kernel.org> [170211 12:34]: > The release callback may be called from two places - file release > operation and kernfs open file draining. kernfs_open_file->mutex is > used to synchronize the two callsites. This unfortunately leads to > possible circular locking because of->mutex is used to protect the > usual kernfs operations which may use locking constructs which are > held while removing and thus draining kernfs files. > > @of->mutex is for synchronizing concurrent kernfs access operations > and all we need here is synchronization between the releaes and drain > paths. As the drain path has to grab kernfs_open_file_mutex anyway, > let's use the mutex to synchronize the release operation instead. > > Signed-off-by: Tejun Heo <tj@kernel.org> > Reported-by: Tony Lindgren <tony@atomide.com> > Fixes: 0e67db2f9fe9 ("kernfs: add kernfs_ops->open/release() callbacks") > --- > Hello, > > Tony, can you please verify that this resolves the lockdep warnings > that you've been seeing on linux-next? Yes thanks this fixes the issue I was seeing: Tested-by: Tony Lindgren <tony@atomide.com> > Greg, this is a fix for the kernfs patches which are being routed > through the cgroup tree. Once Tony confirms, I'll apply this patch on > top. > > Thanks! > > fs/kernfs/file.c | 19 ++++++++++++++----- > 1 file changed, 14 insertions(+), 5 deletions(-) > > --- a/fs/kernfs/file.c > +++ b/fs/kernfs/file.c > @@ -747,10 +747,15 @@ err_out: > static void kernfs_release_file(struct kernfs_node *kn, > struct kernfs_open_file *of) > { > - if (!(kn->flags & KERNFS_HAS_RELEASE)) > - return; > + /* > + * @of is guaranteed to have no other file operations in flight and > + * we just want to synchronize release and drain paths. > + * @kernfs_open_file_mutex is enough. @of->mutex can't be used > + * here because drain path may be called from places which can > + * cause circular dependency. > + */ > + lockdep_assert_held(&kernfs_open_file_mutex); > > - mutex_lock(&of->mutex); > if (!of->released) { > /* > * A file is never detached without being released and we > @@ -760,7 +765,6 @@ static void kernfs_release_file(struct k > kn->attr.ops->release(of); > of->released = true; > } > - mutex_unlock(&of->mutex); > } > > static int kernfs_fop_release(struct inode *inode, struct file *filp) > @@ -768,7 +772,12 @@ static int kernfs_fop_release(struct ino > struct kernfs_node *kn = filp->f_path.dentry->d_fsdata; > struct kernfs_open_file *of = kernfs_of(filp); > > - kernfs_release_file(kn, of); > + if (kn->flags & KERNFS_HAS_RELEASE) { > + mutex_lock(&kernfs_open_file_mutex); > + kernfs_release_file(kn, of); > + mutex_unlock(&kernfs_open_file_mutex); > + } > + > kernfs_put_open_node(kn, of); > seq_release(inode, filp); > kfree(of->prealloc_buf); ^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] kernfs: fix locking around kernfs_ops->release() callback 2017-02-13 17:57 ` Tony Lindgren @ 2017-02-13 18:22 ` Greg Kroah-Hartman 0 siblings, 0 replies; 4+ messages in thread From: Greg Kroah-Hartman @ 2017-02-13 18:22 UTC (permalink / raw) To: Tony Lindgren; +Cc: Tejun Heo, linux-kernel On Mon, Feb 13, 2017 at 09:57:25AM -0800, Tony Lindgren wrote: > * Tejun Heo <tj@kernel.org> [170211 12:34]: > > The release callback may be called from two places - file release > > operation and kernfs open file draining. kernfs_open_file->mutex is > > used to synchronize the two callsites. This unfortunately leads to > > possible circular locking because of->mutex is used to protect the > > usual kernfs operations which may use locking constructs which are > > held while removing and thus draining kernfs files. > > > > @of->mutex is for synchronizing concurrent kernfs access operations > > and all we need here is synchronization between the releaes and drain > > paths. As the drain path has to grab kernfs_open_file_mutex anyway, > > let's use the mutex to synchronize the release operation instead. > > > > Signed-off-by: Tejun Heo <tj@kernel.org> > > Reported-by: Tony Lindgren <tony@atomide.com> > > Fixes: 0e67db2f9fe9 ("kernfs: add kernfs_ops->open/release() callbacks") > > --- > > Hello, > > > > Tony, can you please verify that this resolves the lockdep warnings > > that you've been seeing on linux-next? > > Yes thanks this fixes the issue I was seeing: > > Tested-by: Tony Lindgren <tony@atomide.com> > > > Greg, this is a fix for the kernfs patches which are being routed > > through the cgroup tree. Once Tony confirms, I'll apply this patch on > > top. Great, no objection from me: Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> ^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] kernfs: fix locking around kernfs_ops->release() callback 2017-02-11 20:33 ` [PATCH] kernfs: fix locking around kernfs_ops->release() callback Tejun Heo 2017-02-13 17:57 ` Tony Lindgren @ 2017-02-21 20:50 ` Tejun Heo 1 sibling, 0 replies; 4+ messages in thread From: Tejun Heo @ 2017-02-21 20:50 UTC (permalink / raw) To: linux-kernel, Greg Kroah-Hartman; +Cc: Tony Lindgren On Sun, Feb 12, 2017 at 05:33:02AM +0900, Tejun Heo wrote: > The release callback may be called from two places - file release > operation and kernfs open file draining. kernfs_open_file->mutex is > used to synchronize the two callsites. This unfortunately leads to > possible circular locking because of->mutex is used to protect the > usual kernfs operations which may use locking constructs which are > held while removing and thus draining kernfs files. > > @of->mutex is for synchronizing concurrent kernfs access operations > and all we need here is synchronization between the releaes and drain > paths. As the drain path has to grab kernfs_open_file_mutex anyway, > let's use the mutex to synchronize the release operation instead. > > Signed-off-by: Tejun Heo <tj@kernel.org> > Reported-by: Tony Lindgren <tony@atomide.com> > Fixes: 0e67db2f9fe9 ("kernfs: add kernfs_ops->open/release() callbacks") Applied to cgroup/for-4.11. Thanks. -- tejun ^ permalink raw reply [flat|nested] 4+ messages in thread
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2017-02-11 20:33 ` [PATCH] kernfs: fix locking around kernfs_ops->release() callback Tejun Heo
2017-02-13 17:57 ` Tony Lindgren
2017-02-13 18:22 ` Greg Kroah-Hartman
2017-02-21 20:50 ` Tejun Heo
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