@@ -261,6 +261,25 @@ void flush_delayed_fput(void)
flush_delayed_work(&delayed_fput_work);
}
+/**
+ * fput - put a struct file reference
+ * @file: file of which to put the reference
+ *
+ * This function decrements the reference count for the struct file reference,
+ * and queues it up for destruction if the count goes to zero. In the case of
+ * most tasks we queue it to the task_work infrastructure, which will be run
+ * just before the task returns back to userspace. kthreads however never
+ * return to userspace, so for those we add them to a global list and schedule
+ * a delayed workqueue job to do the final cleanup work.
+ *
+ * Why not just do it synchronously? __fput can involve taking locks of all
+ * sorts, and doing it synchronously means that the callers must take extra care
+ * not to deadlock. That can be very difficult to ensure, so by deferring it
+ * until just before return to userland or to the workqueue, we sidestep that
+ * nastiness. Also, __fput can be quite stack intensive, so doing a final fput
+ * has the possibility of blowing up if we don't take steps to ensure that we
+ * have enough stack space to make it work.
+ */
void fput(struct file *file)
{
if (atomic_long_dec_and_test(&file->f_count)) {
@@ -281,6 +300,7 @@ void fput(struct file *file)
schedule_delayed_work(&delayed_fput_work, 1);
}
}
+EXPORT_SYMBOL(fput);
/*
* synchronous analog of fput(); for kernel threads that might be needed
@@ -299,7 +319,6 @@ void __fput_sync(struct file *file)
}
}
-EXPORT_SYMBOL(fput);
void put_filp(struct file *file)
{
...and move its EXPORT_SYMBOL just below the function. Cc: Al Viro <viro@ZenIV.linux.org.uk> Signed-off-by: Jeff Layton <jeff.layton@primarydata.com> --- fs/file_table.c | 21 ++++++++++++++++++++- 1 file changed, 20 insertions(+), 1 deletion(-)