| Message ID | 20241001225207.2215639-4-andrii@kernel.org (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | uprobes,mm: speculative lockless VMA-to-uprobe lookup | expand |
On Tue, Oct 01, 2024 at 03:52:05PM GMT, Andrii Nakryiko wrote: > 6cf41fcfe099 ("backing file: free directly") switched FMODE_BACKING > files to direct freeing as back then there were no use cases requiring > RCU protected access to such files. > > Now, with speculative lockless VMA-to-uprobe lookup logic, we do need to > have a guarantee that struct file memory is not going to be freed from > under us during speculative check. So add back RCU-delayed freeing > logic. > > We use headless kfree_rcu_mightsleep() variant, as file_free() is only > called for FMODE_BACKING files in might_sleep() context. > > Suggested-by: Suren Baghdasaryan <surenb@google.com> > Cc: Christian Brauner <brauner@kernel.org> > Cc: Amir Goldstein <amir73il@gmail.com> > Signed-off-by: Andrii Nakryiko <andrii@kernel.org> > --- Reviewed-by: Christian Brauner <brauner@kernel.org>
On Thu, Oct 03, 2024 at 11:13:54AM GMT, Christian Brauner wrote: > On Tue, Oct 01, 2024 at 03:52:05PM GMT, Andrii Nakryiko wrote: > > 6cf41fcfe099 ("backing file: free directly") switched FMODE_BACKING > > files to direct freeing as back then there were no use cases requiring > > RCU protected access to such files. > > > > Now, with speculative lockless VMA-to-uprobe lookup logic, we do need to > > have a guarantee that struct file memory is not going to be freed from > > under us during speculative check. So add back RCU-delayed freeing > > logic. > > > > We use headless kfree_rcu_mightsleep() variant, as file_free() is only > > called for FMODE_BACKING files in might_sleep() context. > > > > Suggested-by: Suren Baghdasaryan <surenb@google.com> > > Cc: Christian Brauner <brauner@kernel.org> > > Cc: Amir Goldstein <amir73il@gmail.com> > > Signed-off-by: Andrii Nakryiko <andrii@kernel.org> > > --- > > Reviewed-by: Christian Brauner <brauner@kernel.org> Fwiw, I have another patch series for files that I'm testing that will require me to switch FMODE_BACKING to a SLAB_TYPSAFE_BY_RCU cache. That shouldn't matter for your use-case though.
On Fri, Oct 4, 2024 at 1:01 AM Christian Brauner <brauner@kernel.org> wrote: > > On Thu, Oct 03, 2024 at 11:13:54AM GMT, Christian Brauner wrote: > > On Tue, Oct 01, 2024 at 03:52:05PM GMT, Andrii Nakryiko wrote: > > > 6cf41fcfe099 ("backing file: free directly") switched FMODE_BACKING > > > files to direct freeing as back then there were no use cases requiring > > > RCU protected access to such files. > > > > > > Now, with speculative lockless VMA-to-uprobe lookup logic, we do need to > > > have a guarantee that struct file memory is not going to be freed from > > > under us during speculative check. So add back RCU-delayed freeing > > > logic. > > > > > > We use headless kfree_rcu_mightsleep() variant, as file_free() is only > > > called for FMODE_BACKING files in might_sleep() context. > > > > > > Suggested-by: Suren Baghdasaryan <surenb@google.com> > > > Cc: Christian Brauner <brauner@kernel.org> > > > Cc: Amir Goldstein <amir73il@gmail.com> > > > Signed-off-by: Andrii Nakryiko <andrii@kernel.org> > > > --- > > > > Reviewed-by: Christian Brauner <brauner@kernel.org> > > Fwiw, I have another patch series for files that I'm testing that will > require me to switch FMODE_BACKING to a SLAB_TYPSAFE_BY_RCU cache. That > shouldn't matter for your use-case though. Correct, we assume SLAB_TYPESAFE_BY_RCU semantics for the common case anyways. But hopefully my change won't cause major merge conflicts with your patch set.
On Fri, Oct 04, 2024 at 12:58:00PM GMT, Andrii Nakryiko wrote: > On Fri, Oct 4, 2024 at 1:01 AM Christian Brauner <brauner@kernel.org> wrote: > > > > On Thu, Oct 03, 2024 at 11:13:54AM GMT, Christian Brauner wrote: > > > On Tue, Oct 01, 2024 at 03:52:05PM GMT, Andrii Nakryiko wrote: > > > > 6cf41fcfe099 ("backing file: free directly") switched FMODE_BACKING > > > > files to direct freeing as back then there were no use cases requiring > > > > RCU protected access to such files. > > > > > > > > Now, with speculative lockless VMA-to-uprobe lookup logic, we do need to > > > > have a guarantee that struct file memory is not going to be freed from > > > > under us during speculative check. So add back RCU-delayed freeing > > > > logic. > > > > > > > > We use headless kfree_rcu_mightsleep() variant, as file_free() is only > > > > called for FMODE_BACKING files in might_sleep() context. > > > > > > > > Suggested-by: Suren Baghdasaryan <surenb@google.com> > > > > Cc: Christian Brauner <brauner@kernel.org> > > > > Cc: Amir Goldstein <amir73il@gmail.com> > > > > Signed-off-by: Andrii Nakryiko <andrii@kernel.org> > > > > --- > > > > > > Reviewed-by: Christian Brauner <brauner@kernel.org> > > > > Fwiw, I have another patch series for files that I'm testing that will > > require me to switch FMODE_BACKING to a SLAB_TYPSAFE_BY_RCU cache. That > > shouldn't matter for your use-case though. > > Correct, we assume SLAB_TYPESAFE_BY_RCU semantics for the common case > anyways. But hopefully my change won't cause major merge conflicts > with your patch set. Please drop this patch and pull the following tag which adds SLAB_TYPE_SAFE_BY_RCU protection for FMODE_BACKING files aligning them with regular files lifetime (even though not needed). The branch the tag is based on is stable and won't change anymore: git pull -S git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git tags/vfs-6.13.for-bpf.file
On Wed, Oct 9, 2024 at 3:36 AM Christian Brauner <brauner@kernel.org> wrote: > > On Fri, Oct 04, 2024 at 12:58:00PM GMT, Andrii Nakryiko wrote: > > On Fri, Oct 4, 2024 at 1:01 AM Christian Brauner <brauner@kernel.org> wrote: > > > > > > On Thu, Oct 03, 2024 at 11:13:54AM GMT, Christian Brauner wrote: > > > > On Tue, Oct 01, 2024 at 03:52:05PM GMT, Andrii Nakryiko wrote: > > > > > 6cf41fcfe099 ("backing file: free directly") switched FMODE_BACKING > > > > > files to direct freeing as back then there were no use cases requiring > > > > > RCU protected access to such files. > > > > > > > > > > Now, with speculative lockless VMA-to-uprobe lookup logic, we do need to > > > > > have a guarantee that struct file memory is not going to be freed from > > > > > under us during speculative check. So add back RCU-delayed freeing > > > > > logic. > > > > > > > > > > We use headless kfree_rcu_mightsleep() variant, as file_free() is only > > > > > called for FMODE_BACKING files in might_sleep() context. > > > > > > > > > > Suggested-by: Suren Baghdasaryan <surenb@google.com> > > > > > Cc: Christian Brauner <brauner@kernel.org> > > > > > Cc: Amir Goldstein <amir73il@gmail.com> > > > > > Signed-off-by: Andrii Nakryiko <andrii@kernel.org> > > > > > --- > > > > > > > > Reviewed-by: Christian Brauner <brauner@kernel.org> > > > > > > Fwiw, I have another patch series for files that I'm testing that will > > > require me to switch FMODE_BACKING to a SLAB_TYPSAFE_BY_RCU cache. That > > > shouldn't matter for your use-case though. > > > > Correct, we assume SLAB_TYPESAFE_BY_RCU semantics for the common case > > anyways. But hopefully my change won't cause major merge conflicts > > with your patch set. > > Please drop this patch and pull the following tag which adds > SLAB_TYPE_SAFE_BY_RCU protection for FMODE_BACKING files aligning them > with regular files lifetime (even though not needed). The branch the tag > is based on is stable and won't change anymore: > > git pull -S git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git tags/vfs-6.13.for-bpf.file Ok, will drop. It will on Peter to pull this tag into tip/perf/core, but I'll mention all this in the cover letter (and will pull locally for testing, of course). Thanks.
diff --git a/fs/file_table.c b/fs/file_table.c index ca7843dde56d..257691d358ee 100644 --- a/fs/file_table.c +++ b/fs/file_table.c @@ -68,7 +68,7 @@ static inline void file_free(struct file *f) put_cred(f->f_cred); if (unlikely(f->f_mode & FMODE_BACKING)) { path_put(backing_file_user_path(f)); - kfree(backing_file(f)); + kfree_rcu_mightsleep(backing_file(f)); } else { kmem_cache_free(filp_cachep, f); }
6cf41fcfe099 ("backing file: free directly") switched FMODE_BACKING files to direct freeing as back then there were no use cases requiring RCU protected access to such files. Now, with speculative lockless VMA-to-uprobe lookup logic, we do need to have a guarantee that struct file memory is not going to be freed from under us during speculative check. So add back RCU-delayed freeing logic. We use headless kfree_rcu_mightsleep() variant, as file_free() is only called for FMODE_BACKING files in might_sleep() context. Suggested-by: Suren Baghdasaryan <surenb@google.com> Cc: Christian Brauner <brauner@kernel.org> Cc: Amir Goldstein <amir73il@gmail.com> Signed-off-by: Andrii Nakryiko <andrii@kernel.org> --- fs/file_table.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)