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get rid of the magic around f_count in aio

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__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 <[email protected]>
This commit is contained in:
Al Viro 2010-05-26 15:13:55 -04:00
commit d7065da038
4 changed files with 14 additions and 15 deletions
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6
fs/aio.c
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@ -527,7 +527,7 @@ static void aio_fput_routine(struct work_struct *data)
/* 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 @@ static int __aio_put_req(struct kioctx *ctx, struct kiocb *req)
/*
* 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);