On Thu, Mar 22, 2018 at 04:52:55PM +0000, Al Viro wrote: > On Wed, Mar 21, 2018 at 08:40:10AM +0100, Christoph Hellwig wrote: > > Simple one-shot poll through the io_submit() interface. To poll for > > a file descriptor the application should submit an iocb of type > > IOCB_CMD_POLL. It will poll the fd for the events specified in the > > the first 32 bits of the aio_buf field of the iocb. > > > > Unlike poll or epoll without EPOLLONESHOT this interface always works > > in one shot mode, that is once the iocb is completed, it will have to be > > resubmitted. > > AFAICS, your wakeup can race with io_cancel(), leading to double fput(). > You are checking the "somebody had committed itself to cancelling that > thing" bit outside of ->ctx_lock on the wakeup side, and I don't see > anything to prevent both getting to __aio_poll_complete() on the same > iocb, with obvious results. True. Probably wants something like this to fix, although for this is entirely untested: diff --git a/fs/aio.c b/fs/aio.c index 38b408129697..66d5cc272617 100644 --- a/fs/aio.c +++ b/fs/aio.c @@ -187,8 +187,9 @@ struct aio_kiocb { * for cancellation */ unsigned int flags; /* protected by ctx->ctx_lock */ -#define AIO_IOCB_DELAYED_CANCEL (1 << 0) -#define AIO_IOCB_CANCELLED (1 << 1) +#define AIO_IOCB_CAN_CANCEL (1 << 0) +#define AIO_IOCB_DELAYED_CANCEL (1 << 1) +#define AIO_IOCB_CANCELLED (1 << 2) /* * If the aio_resfd field of the userspace iocb is not zero, @@ -568,7 +569,7 @@ static void __kiocb_set_cancel_fn(struct aio_kiocb *req, spin_lock_irqsave(&ctx->ctx_lock, flags); list_add_tail(&req->ki_list, &ctx->active_reqs); req->ki_cancel = cancel; - req->flags |= iocb_flags; + req->flags |= (AIO_IOCB_CAN_CANCEL | iocb_flags); spin_unlock_irqrestore(&ctx->ctx_lock, flags); } @@ -1086,22 +1087,30 @@ static struct kioctx *lookup_ioctx(unsigned long ctx_id) return ret; } +#define AIO_COMPLETE_CANCEL (1 << 0) + /* aio_complete * Called when the io request on the given iocb is complete. */ -static void aio_complete(struct aio_kiocb *iocb, long res, long res2) +static bool aio_complete(struct aio_kiocb *iocb, long res, long res2, + unsigned complete_flags) { struct kioctx *ctx = iocb->ki_ctx; struct aio_ring *ring; struct io_event *ev_page, *event; unsigned tail, pos, head; - unsigned long flags; - - if (!list_empty_careful(iocb->ki_list.next)) { - unsigned long flags; + unsigned long flags; + if (iocb->flags & AIO_IOCB_CAN_CANCEL) { spin_lock_irqsave(&ctx->ctx_lock, flags); - list_del(&iocb->ki_list); + if (!(complete_flags & AIO_COMPLETE_CANCEL) && + (iocb->flags & AIO_IOCB_CANCELLED)) { + spin_unlock_irqrestore(&ctx->ctx_lock, flags); + return false; + } + + if (!list_empty(&iocb->ki_list)) + list_del(&iocb->ki_list); spin_unlock_irqrestore(&ctx->ctx_lock, flags); } @@ -1177,6 +1186,7 @@ static void aio_complete(struct aio_kiocb *iocb, long res, long res2) wake_up(&ctx->wait); percpu_ref_put(&ctx->reqs); + return true; } /* aio_read_events_ring @@ -1425,6 +1435,7 @@ SYSCALL_DEFINE1(io_destroy, aio_context_t, ctx) static void aio_complete_rw(struct kiocb *kiocb, long res, long res2) { struct aio_kiocb *iocb = container_of(kiocb, struct aio_kiocb, rw); + struct file *file = kiocb->ki_filp; WARN_ON_ONCE(is_sync_kiocb(kiocb)); @@ -1440,8 +1451,8 @@ static void aio_complete_rw(struct kiocb *kiocb, long res, long res2) file_end_write(kiocb->ki_filp); } - fput(kiocb->ki_filp); - aio_complete(iocb, res, res2); + if (aio_complete(iocb, res, res2, 0)) + fput(file); } static int aio_prep_rw(struct kiocb *req, struct iocb *iocb) @@ -1584,11 +1595,13 @@ static ssize_t aio_write(struct kiocb *req, struct iocb *iocb, bool vectored, static void aio_fsync_work(struct work_struct *work) { struct fsync_iocb *req = container_of(work, struct fsync_iocb, work); + struct aio_kiocb *iocb = container_of(req, struct aio_kiocb, fsync); + struct file *file = req->file; int ret; ret = vfs_fsync(req->file, req->datasync); - fput(req->file); - aio_complete(container_of(req, struct aio_kiocb, fsync), ret, 0); + if (aio_complete(iocb, ret, 0, 0)) + fput(file); } static int aio_fsync(struct fsync_iocb *req, struct iocb *iocb, bool datasync) @@ -1617,27 +1630,23 @@ static int aio_fsync(struct fsync_iocb *req, struct iocb *iocb, bool datasync) return ret; } -static void __aio_complete_poll(struct poll_iocb *req, __poll_t mask) -{ - fput(req->file); - aio_complete(container_of(req, struct aio_kiocb, poll), - mangle_poll(mask), 0); -} - static void aio_complete_poll(struct poll_iocb *req, __poll_t mask) { struct aio_kiocb *iocb = container_of(req, struct aio_kiocb, poll); + struct file *file = req->file; - if (!(iocb->flags & AIO_IOCB_CANCELLED)) - __aio_complete_poll(req, mask); + if (aio_complete(iocb, mangle_poll(mask), 0, 0)) + fput(file); } static int aio_poll_cancel(struct kiocb *rw) { struct aio_kiocb *iocb = container_of(rw, struct aio_kiocb, rw); + struct file *file = iocb->poll.file; remove_wait_queue(iocb->poll.head, &iocb->poll.wait); - __aio_complete_poll(&iocb->poll, 0); /* no events to report */ + if (aio_complete(iocb, 0, 0, AIO_COMPLETE_CANCEL)) + fput(file); return 0; } -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html