get rid of the magic around f_count in aio
__aio_put_req() plays sick games with file refcount. What
it wants is fput() from atomic context; it's almost always
done with f_count > 1, so they only have to deal with delayed
work in rare cases when their reference happens to be the
last one. Current code decrements f_count and if it hasn't
hit 0, everything is fine. Otherwise it keeps a pointer
to struct file (with zero f_count!) around and has delayed
work do __fput() on it.
Better way to do it: use atomic_long_add_unless( , -1, 1)
instead of !atomic_long_dec_and_test(). IOW, decrement it
only if it's not the last reference, leave refcount alone
if it was. And use normal fput() in delayed work.
I've made that atomic_long_add_unless call a new helper -
fput_atomic(). Drops a reference to file if it's safe to
do in atomic (i.e. if that's not the last one), tells if
it had been able to do that. aio.c converted to it, __fput()
use is gone. req->ki_file *always* contributes to refcount
now. And __fput() became static.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/aio.c b/fs/aio.c
index 48fdeeb..1ccf25c 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -527,7 +527,7 @@
/* Complete the fput(s) */
if (req->ki_filp != NULL)
- __fput(req->ki_filp);
+ fput(req->ki_filp);
/* Link the iocb into the context's free list */
spin_lock_irq(&ctx->ctx_lock);
@@ -560,11 +560,11 @@
/*
* Try to optimize the aio and eventfd file* puts, by avoiding to
- * schedule work in case it is not __fput() time. In normal cases,
+ * schedule work in case it is not final fput() time. In normal cases,
* we would not be holding the last reference to the file*, so
* this function will be executed w/out any aio kthread wakeup.
*/
- if (unlikely(atomic_long_dec_and_test(&req->ki_filp->f_count))) {
+ if (unlikely(!fput_atomic(req->ki_filp))) {
get_ioctx(ctx);
spin_lock(&fput_lock);
list_add(&req->ki_list, &fput_head);