From 33f775eea185e8df7701c4afc2c8fcee85c83282 Mon Sep 17 00:00:00 2001 From: Paolo 'Blaisorblade' Giarrusso Date: Mon, 30 Oct 2006 22:07:08 -0800 Subject: [PATCH] [PATCH] uml ubd driver: ubd_io_lock usage fixup Add some comments about requirements for ubd_io_lock and expand its use. When an irq signals that the "controller" (i.e. another thread on the host, which does the actual requests and is the only one blocked on I/O on the host) has done some work, we call again the request function ourselves (do_ubd_request). We now do that with ubd_io_lock held - that's useful to protect against concurrent calls to elv_next_request and so on. XXX: Maybe we shouldn't call at all the request function. Input needed on this. Are we supposed to plug and unplug the queue? That code "indirectly" does that by setting a flag, called do_ubd, which makes the request function return (it's a residual of 2.4 block layer interface). Meanwhile, however, merge this patch, which improves things. Cc: Jens Axboe Signed-off-by: Paolo 'Blaisorblade' Giarrusso Cc: Jeff Dike Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- arch/um/drivers/ubd_kern.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/arch/um/drivers/ubd_kern.c b/arch/um/drivers/ubd_kern.c index a3061ae39b3b..6cd8988e8fd0 100644 --- a/arch/um/drivers/ubd_kern.c +++ b/arch/um/drivers/ubd_kern.c @@ -106,6 +106,8 @@ static inline void ubd_set_bit(__u64 bit, unsigned char *data) #define DRIVER_NAME "uml-blkdev" +/* Can be taken in interrupt context, and is passed to the block layer to lock + * the request queue. Kernel side code knows that. */ static DEFINE_SPINLOCK(ubd_io_lock); static DEFINE_MUTEX(ubd_lock); @@ -497,6 +499,8 @@ static void __ubd_finish(struct request *req, int error) end_request(req, 1); } +/* Callable only from interrupt context - otherwise you need to do + * spin_lock_irq()/spin_lock_irqsave() */ static inline void ubd_finish(struct request *req, int error) { spin_lock(&ubd_io_lock); @@ -504,7 +508,7 @@ static inline void ubd_finish(struct request *req, int error) spin_unlock(&ubd_io_lock); } -/* Called without ubd_io_lock held */ +/* Called without ubd_io_lock held, and only in interrupt context. */ static void ubd_handler(void) { struct io_thread_req req; @@ -525,7 +529,9 @@ static void ubd_handler(void) ubd_finish(rq, req.error); reactivate_fd(thread_fd, UBD_IRQ); + spin_lock(&ubd_io_lock); do_ubd_request(ubd_queue); + spin_unlock(&ubd_io_lock); } static irqreturn_t ubd_intr(int irq, void *dev)