From bdb2fd7fc56e197a63c0b0e7e07d25d5e20e7c72 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Sat, 27 Aug 2022 19:04:35 -1000 Subject: [PATCH] kernfs: Skip kernfs_drain_open_files() more aggressively Track the number of mmapped files and files that need to be released and skip kernfs_drain_open_file() if both are zero, which are the precise conditions which require draining open_files. The early exit test is factored into kernfs_should_drain_open_files() which is now tested by kernfs_drain_open_files()'s caller - kernfs_drain(). This isn't a meaningful optimization on its own but will enable future stand-alone kernfs_deactivate() implementation. v2: Chengming noticed that on->nr_to_release was leaking after ->open() failure. Fix it by telling kernfs_unlink_open_file() that it's called from the ->open() fail path and should dec the counter. Use kzalloc() to allocate kernfs_open_node so that the tracking fields are correctly initialized. Cc: Chengming Zhou Tested-by: Chengming Zhou Reviewed-by: Chengming Zhou Signed-off-by: Tejun Heo Link: https://lore.kernel.org/r/20220828050440.734579-5-tj@kernel.org Signed-off-by: Greg Kroah-Hartman --- fs/kernfs/dir.c | 3 ++- fs/kernfs/file.c | 65 +++++++++++++++++++++++++++++++-------------- fs/kernfs/kernfs-internal.h | 1 + 3 files changed, 48 insertions(+), 21 deletions(-) diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c index 1cc88ba..8ae44db 100644 --- a/fs/kernfs/dir.c +++ b/fs/kernfs/dir.c @@ -489,7 +489,8 @@ static void kernfs_drain(struct kernfs_node *kn) rwsem_release(&kn->dep_map, _RET_IP_); } - kernfs_drain_open_files(kn); + if (kernfs_should_drain_open_files(kn)) + kernfs_drain_open_files(kn); down_write(&root->kernfs_rwsem); } diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c index 7060a2a..9ab6c92 100644 --- a/fs/kernfs/file.c +++ b/fs/kernfs/file.c @@ -23,6 +23,8 @@ struct kernfs_open_node { atomic_t event; wait_queue_head_t poll; struct list_head files; /* goes through kernfs_open_file.list */ + unsigned int nr_mmapped; + unsigned int nr_to_release; }; /* @@ -527,6 +529,7 @@ static int kernfs_fop_mmap(struct file *file, struct vm_area_struct *vma) rc = 0; of->mmapped = true; + of_on(of)->nr_mmapped++; of->vm_ops = vma->vm_ops; vma->vm_ops = &kernfs_vm_ops; out_put: @@ -562,7 +565,7 @@ static int kernfs_get_open_node(struct kernfs_node *kn, if (!on) { /* not there, initialize a new one */ - on = kmalloc(sizeof(*on), GFP_KERNEL); + on = kzalloc(sizeof(*on), GFP_KERNEL); if (!on) { mutex_unlock(mutex); return -ENOMEM; @@ -574,6 +577,8 @@ static int kernfs_get_open_node(struct kernfs_node *kn, } list_add_tail(&of->list, &on->files); + if (kn->flags & KERNFS_HAS_RELEASE) + on->nr_to_release++; mutex_unlock(mutex); return 0; @@ -584,6 +589,7 @@ static int kernfs_get_open_node(struct kernfs_node *kn, * * @kn: target kernfs_node * @of: associated kernfs_open_file + * @open_failed: ->open() failed, cancel ->release() * * Unlink @of from list of @kn's associated open files. If list of * associated open files becomes empty, disassociate and free @@ -593,7 +599,8 @@ static int kernfs_get_open_node(struct kernfs_node *kn, * None. */ static void kernfs_unlink_open_file(struct kernfs_node *kn, - struct kernfs_open_file *of) + struct kernfs_open_file *of, + bool open_failed) { struct kernfs_open_node *on; struct mutex *mutex; @@ -606,8 +613,16 @@ static void kernfs_unlink_open_file(struct kernfs_node *kn, return; } - if (of) + if (of) { + if (kn->flags & KERNFS_HAS_RELEASE) { + WARN_ON_ONCE(of->released == open_failed); + if (open_failed) + on->nr_to_release--; + } + if (of->mmapped) + on->nr_mmapped--; list_del(&of->list); + } if (list_empty(&on->files)) { rcu_assign_pointer(kn->attr.open, NULL); @@ -734,7 +749,7 @@ static int kernfs_fop_open(struct inode *inode, struct file *file) return 0; err_put_node: - kernfs_unlink_open_file(kn, of); + kernfs_unlink_open_file(kn, of, true); err_seq_release: seq_release(inode, file); err_free: @@ -766,6 +781,7 @@ static void kernfs_release_file(struct kernfs_node *kn, */ kn->attr.ops->release(of); of->released = true; + of_on(of)->nr_to_release--; } } @@ -782,7 +798,7 @@ static int kernfs_fop_release(struct inode *inode, struct file *filp) mutex_unlock(mutex); } - kernfs_unlink_open_file(kn, of); + kernfs_unlink_open_file(kn, of, false); seq_release(inode, filp); kfree(of->prealloc_buf); kfree(of); @@ -790,25 +806,30 @@ static int kernfs_fop_release(struct inode *inode, struct file *filp) return 0; } -void kernfs_drain_open_files(struct kernfs_node *kn) +bool kernfs_should_drain_open_files(struct kernfs_node *kn) { struct kernfs_open_node *on; - struct kernfs_open_file *of; - struct mutex *mutex; - - if (!(kn->flags & (KERNFS_HAS_MMAP | KERNFS_HAS_RELEASE))) - return; + bool ret; /* - * lockless opportunistic check is safe below because no one is adding to - * ->attr.open at this point of time. This check allows early bail out - * if ->attr.open is already NULL. kernfs_unlink_open_file makes - * ->attr.open NULL only while holding kernfs_open_file_mutex so below - * check under kernfs_open_file_mutex_ptr(kn) will ensure bailing out if - * ->attr.open became NULL while waiting for the mutex. + * @kn being deactivated guarantees that @kn->attr.open can't change + * beneath us making the lockless test below safe. */ - if (!rcu_access_pointer(kn->attr.open)) - return; + WARN_ON_ONCE(atomic_read(&kn->active) != KN_DEACTIVATED_BIAS); + + rcu_read_lock(); + on = rcu_dereference(kn->attr.open); + ret = on && (on->nr_mmapped || on->nr_to_release); + rcu_read_unlock(); + + return ret; +} + +void kernfs_drain_open_files(struct kernfs_node *kn) +{ + struct kernfs_open_node *on; + struct kernfs_open_file *of; + struct mutex *mutex; mutex = kernfs_open_file_mutex_lock(kn); on = kernfs_deref_open_node_locked(kn); @@ -820,13 +841,17 @@ void kernfs_drain_open_files(struct kernfs_node *kn) list_for_each_entry(of, &on->files, list) { struct inode *inode = file_inode(of->file); - if (kn->flags & KERNFS_HAS_MMAP) + if (of->mmapped) { unmap_mapping_range(inode->i_mapping, 0, 0, 1); + of->mmapped = false; + on->nr_mmapped--; + } if (kn->flags & KERNFS_HAS_RELEASE) kernfs_release_file(kn, of); } + WARN_ON_ONCE(on->nr_mmapped || on->nr_to_release); mutex_unlock(mutex); } diff --git a/fs/kernfs/kernfs-internal.h b/fs/kernfs/kernfs-internal.h index 3ae214d..fc5821e 100644 --- a/fs/kernfs/kernfs-internal.h +++ b/fs/kernfs/kernfs-internal.h @@ -157,6 +157,7 @@ struct kernfs_node *kernfs_new_node(struct kernfs_node *parent, */ extern const struct file_operations kernfs_file_fops; +bool kernfs_should_drain_open_files(struct kernfs_node *kn); void kernfs_drain_open_files(struct kernfs_node *kn); /* -- 2.7.4