file: Replace fcheck_files with files_lookup_fd_rcu

This change renames fcheck_files to files_lookup_fd_rcu.  All of the
remaining callers take the rcu_read_lock before calling this function
so the _rcu suffix is appropriate.  This change also tightens up the
debug check to verify that all callers hold the rcu_read_lock.

All callers that used to call files_check with the files->file_lock
held have now been changed to call files_lookup_fd_locked.

This change of name has helped remind me of which locks and which
guarantees are in place helping me to catch bugs later in the
patchset.

The need for better names became apparent in the last round of
discussion of this set of changes[1].

[1] https://lkml.kernel.org/r/CAHk-=wj8BQbgJFLa+J0e=iT-1qpmCRTbPAJ8gd6MJQ=kbRPqyQ@mail.gmail.com
Link: https://lkml.kernel.org/r/20201120231441.29911-9-ebiederm@xmission.com
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>

diff --git a/Documentation/filesystems/files.rst b/Documentation/filesystems/files.rst
index cbf8e57376bf681ee697c2499726fb946d2dd8ca..ea75acdb632c045fc6d9012e2264a699fed9e7f2 100644 (file)
--- a/Documentation/filesystems/files.rst
+++ b/Documentation/filesystems/files.rst
@@ -62,7 +62,7 @@ the fdtable structure -
    be held.
 
 4. To look up the file structure given an fd, a reader
-   must use either fcheck() or fcheck_files() APIs. These
+   must use either fcheck() or files_lookup_fd_rcu() APIs. These
    take care of barrier requirements due to lock-free lookup.
 
    An example::
@@ -84,7 +84,7 @@ the fdtable structure -
    on ->f_count::
 
        rcu_read_lock();
-       file = fcheck_files(files, fd);
+       file = files_lookup_fd_rcu(files, fd);
        if (file) {
                if (atomic_long_inc_not_zero(&file->f_count))
                        *fput_needed = 1;
@@ -104,7 +104,7 @@ the fdtable structure -
    lock-free, they must be installed using rcu_assign_pointer()
    API. If they are looked up lock-free, rcu_dereference()
    must be used. However it is advisable to use files_fdtable()
-   and fcheck()/fcheck_files() which take care of these issues.
+   and fcheck()/files_lookup_fd_rcu() which take care of these issues.
 
 7. While updating, the fdtable pointer must be looked up while
    holding files->file_lock. If ->file_lock is dropped, then

diff --git a/fs/file.c b/fs/file.c
index 9d0e91168be185ecd2a05b3fcc581edd674e604f..5861c4f894195ce8fb3334fd15b38475dd688aef 100644 (file)
--- a/fs/file.c
+++ b/fs/file.c
@@ -814,7 +814,7 @@ static struct file *__fget_files(struct files_struct *files, unsigned int fd,
 
        rcu_read_lock();
 loop:
-       file = fcheck_files(files, fd);
+       file = files_lookup_fd_rcu(files, fd);
        if (file) {
                /* File object ref couldn't be taken.
                 * dup2() atomicity guarantee is the reason
@@ -1127,7 +1127,7 @@ SYSCALL_DEFINE2(dup2, unsigned int, oldfd, unsigned int, newfd)
                int retval = oldfd;
 
                rcu_read_lock();
-               if (!fcheck_files(files, oldfd))
+               if (!files_lookup_fd_rcu(files, oldfd))
                        retval = -EBADF;
                rcu_read_unlock();
                return retval;

diff --git a/fs/proc/fd.c b/fs/proc/fd.c
index 2cca9bca3b3a3ff110e856368bbaa764fc0b2587..3dec44d7c5c5c499a90dc3423e328889ecb900e5 100644 (file)
--- a/fs/proc/fd.c
+++ b/fs/proc/fd.c
@@ -90,7 +90,7 @@ static bool tid_fd_mode(struct task_struct *task, unsigned fd, fmode_t *mode)
                return false;
 
        rcu_read_lock();
-       file = fcheck_files(files, fd);
+       file = files_lookup_fd_rcu(files, fd);
        if (file)
                *mode = file->f_mode;
        rcu_read_unlock();
@@ -243,7 +243,7 @@ static int proc_readfd_common(struct file *file, struct dir_context *ctx,
                char name[10 + 1];
                unsigned int len;
 
-               f = fcheck_files(files, fd);
+               f = files_lookup_fd_rcu(files, fd);
                if (!f)
                        continue;
                data.mode = f->f_mode;

diff --git a/include/linux/fdtable.h b/include/linux/fdtable.h
index fda4b81dd735ba8dbc6b97f6231d7af3047820ec..fa8c402a77901d639647c455ee0dbb1b6c40cb3d 100644 (file)
--- a/include/linux/fdtable.h
+++ b/include/linux/fdtable.h
@@ -98,10 +98,9 @@ static inline struct file *files_lookup_fd_locked(struct files_struct *files, un
        return files_lookup_fd_raw(files, fd);
 }
 
-static inline struct file *fcheck_files(struct files_struct *files, unsigned int fd)
+static inline struct file *files_lookup_fd_rcu(struct files_struct *files, unsigned int fd)
 {
-       RCU_LOCKDEP_WARN(!rcu_read_lock_held() &&
-                          !lockdep_is_held(&files->file_lock),
+       RCU_LOCKDEP_WARN(!rcu_read_lock_held(),
                           "suspicious rcu_dereference_check() usage");
        return files_lookup_fd_raw(files, fd);
 }
@@ -109,7 +108,7 @@ static inline struct file *fcheck_files(struct files_struct *files, unsigned int
 /*
  * Check whether the specified fd has an open file.
  */
-#define fcheck(fd)     fcheck_files(current->files, fd)
+#define fcheck(fd)     files_lookup_fd_rcu(current->files, fd)
 
 struct task_struct;
 

diff --git a/kernel/bpf/task_iter.c b/kernel/bpf/task_iter.c
index 5b6af30bfbcd887a09c3ebc8762589f138c12e8f..5ab2ccfb96cbec139b75ecac37ccc6ceed317f2e 100644 (file)
--- a/kernel/bpf/task_iter.c
+++ b/kernel/bpf/task_iter.c
@@ -183,7 +183,7 @@ again:
        for (; curr_fd < max_fds; curr_fd++) {
                struct file *f;
 
-               f = fcheck_files(curr_files, curr_fd);
+               f = files_lookup_fd_rcu(curr_files, curr_fd);
                if (!f)
                        continue;
                if (!get_file_rcu(f))

diff --git a/kernel/kcmp.c b/kernel/kcmp.c
index 87c48c0104adef088693183ec65db55050815189..990717c1aed331c575815df3fd4e8ba28e79b3d5 100644 (file)
--- a/kernel/kcmp.c
+++ b/kernel/kcmp.c
@@ -67,7 +67,7 @@ get_file_raw_ptr(struct task_struct *task, unsigned int idx)
        rcu_read_lock();
 
        if (task->files)
-               file = fcheck_files(task->files, idx);
+               file = files_lookup_fd_rcu(task->files, idx);
 
        rcu_read_unlock();
        task_unlock(task);