From 5f820f648c92a5ecc771a96b3c29aa6e90013bba Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Tue, 6 Jan 2009 14:40:59 -0800 Subject: poll: allow f_op->poll to sleep f_op->poll is the only vfs operation which is not allowed to sleep. It's because poll and select implementation used task state to synchronize against wake ups, which doesn't have to be the case anymore as wait/wake interface can now use custom wake up functions. The non-sleep restriction can be a bit tricky because ->poll is not called from an atomic context and the result of accidentally sleeping in ->poll only shows up as temporary busy looping when the timing is right or rather wrong. This patch converts poll/select to use custom wake up function and use separate triggered variable to synchronize against wake up events. The only added overhead is an extra function call during wake up and negligible. This patch removes the one non-sleep exception from vfs locking rules and is beneficial to userland filesystem implementations like FUSE, 9p or peculiar fs like spufs as it's very difficult for those to implement non-sleeping poll method. While at it, make the following cosmetic changes to make poll.h and select.c checkpatch friendly. * s/type * symbol/type *symbol/ : three places in poll.h * remove blank line before EXPORT_SYMBOL() : two places in select.c Oleg: spotted missing barrier in poll_schedule_timeout() Davide: spotted missing write barrier in pollwake() Signed-off-by: Tejun Heo Cc: Eric Van Hensbergen Cc: Ron Minnich Cc: Ingo Molnar Cc: Christoph Hellwig Signed-off-by: Miklos Szeredi Cc: Davide Libenzi Cc: Brad Boyer Cc: Al Viro Cc: Roland McGrath Cc: Mauro Carvalho Chehab Signed-off-by: Andrew Morton Cc: Davide Libenzi Cc: Oleg Nesterov Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- drivers/media/video/v4l1-compat.c | 4 +--- 1 file changed, 1 insertion(+), 3 deletions(-) (limited to 'drivers/media') diff --git a/drivers/media/video/v4l1-compat.c b/drivers/media/video/v4l1-compat.c index d450cab20be4..b617bf05e2d7 100644 --- a/drivers/media/video/v4l1-compat.c +++ b/drivers/media/video/v4l1-compat.c @@ -203,7 +203,6 @@ static int poll_one(struct file *file, struct poll_wqueues *pwq) table = &pwq->pt; for (;;) { int mask; - set_current_state(TASK_INTERRUPTIBLE); mask = file->f_op->poll(file, table); if (mask & POLLIN) break; @@ -212,9 +211,8 @@ static int poll_one(struct file *file, struct poll_wqueues *pwq) retval = -ERESTARTSYS; break; } - schedule(); + poll_schedule(pwq, TASK_INTERRUPTIBLE); } - set_current_state(TASK_RUNNING); poll_freewait(pwq); return retval; } -- cgit v1.2.2