diff options
Diffstat (limited to 'fs/file.c')
| -rw-r--r-- | fs/file.c | 77 |
1 files changed, 70 insertions, 7 deletions
diff --git a/fs/file.c b/fs/file.c index 7251d215048d..efd9959b03c2 100644 --- a/fs/file.c +++ b/fs/file.c @@ -20,10 +20,73 @@ #include <linux/spinlock.h> #include <linux/rcupdate.h> #include <linux/close_range.h> +#include <linux/file_ref.h> #include <net/sock.h> #include "internal.h" +/** + * __file_ref_put - Slowpath of file_ref_put() + * @ref: Pointer to the reference count + * @cnt: Current reference count + * + * Invoked when the reference count is outside of the valid zone. + * + * Return: + * True if this was the last reference with no future references + * possible. This signals the caller that it can safely schedule the + * object, which is protected by the reference counter, for + * deconstruction. + * + * False if there are still active references or the put() raced + * with a concurrent get()/put() pair. Caller is not allowed to + * deconstruct the protected object. + */ +bool __file_ref_put(file_ref_t *ref, unsigned long cnt) +{ + /* Did this drop the last reference? */ + if (likely(cnt == FILE_REF_NOREF)) { + /* + * Carefully try to set the reference count to FILE_REF_DEAD. + * + * This can fail if a concurrent get() operation has + * elevated it again or the corresponding put() even marked + * it dead already. Both are valid situations and do not + * require a retry. If this fails the caller is not + * allowed to deconstruct the object. + */ + if (!atomic_long_try_cmpxchg_release(&ref->refcnt, &cnt, FILE_REF_DEAD)) + return false; + + /* + * The caller can safely schedule the object for + * deconstruction. Provide acquire ordering. + */ + smp_acquire__after_ctrl_dep(); + return true; + } + + /* + * If the reference count was already in the dead zone, then this + * put() operation is imbalanced. Warn, put the reference count back to + * DEAD and tell the caller to not deconstruct the object. + */ + if (WARN_ONCE(cnt >= FILE_REF_RELEASED, "imbalanced put on file reference count")) { + atomic_long_set(&ref->refcnt, FILE_REF_DEAD); + return false; + } + + /* + * This is a put() operation on a saturated refcount. Restore the + * mean saturation value and tell the caller to not deconstruct the + * object. + */ + if (cnt > FILE_REF_MAXREF) + atomic_long_set(&ref->refcnt, FILE_REF_SATURATED); + return false; +} +EXPORT_SYMBOL_GPL(__file_ref_put); + unsigned int sysctl_nr_open __read_mostly = 1024*1024; unsigned int sysctl_nr_open_min = BITS_PER_LONG; /* our min() is unusable in constant expressions ;-/ */ @@ -820,7 +883,7 @@ static struct file *__get_file_rcu(struct file __rcu **f) if (!file) return NULL; - if (unlikely(!atomic_long_inc_not_zero(&file->f_count))) + if (unlikely(!file_ref_get(&file->f_ref))) return ERR_PTR(-EAGAIN); file_reloaded = rcu_dereference_raw(*f); @@ -834,8 +897,8 @@ static struct file *__get_file_rcu(struct file __rcu **f) OPTIMIZER_HIDE_VAR(file_reloaded_cmp); /* - * atomic_long_inc_not_zero() above provided a full memory - * barrier when we acquired a reference. + * file_ref_get() above provided a full memory barrier when we + * acquired a reference. * * This is paired with the write barrier from assigning to the * __rcu protected file pointer so that if that pointer still @@ -933,11 +996,11 @@ static inline struct file *__fget_files_rcu(struct files_struct *files, * We need to confirm it by incrementing the refcount * and then check the lookup again. * - * atomic_long_inc_not_zero() gives us a full memory - * barrier. We only really need an 'acquire' one to - * protect the loads below, but we don't have that. + * file_ref_get() gives us a full memory barrier. We + * only really need an 'acquire' one to protect the + * loads below, but we don't have that. */ - if (unlikely(!atomic_long_inc_not_zero(&file->f_count))) + if (unlikely(!file_ref_get(&file->f_ref))) continue; /* |