On Wed, 23 Aug 2006 01:06:02 -0700
Stephane Eranian <[email protected]> wrote:
> This patch contains the new generic file related functions.
>
> A perfmon2 context is identified by a file descriptor and
> we leverage certain kernel mechanisms related to files.
> In particular we use:
> - read
> - select, poll
> - fcntl
> - close
> - mmap
>
> Support for those operations is implemented in perfmon_file.c.
>
>
> pfm_read():
> - implements the callback for the read() operation. It is used to extract
> overflow notification messages. Only one message can be extracted per call.
> This can be a blocking call is the file is setup that way.
>
> pfm_poll():
> - support for poll() and select()
>
> pfm_fasync():
> - support for FASYNC for fcntl(). Is used to received asynchronous notifications via SIGIO
>
> pfm_mmap():
> - handle remapping read-only of the kernel sampling buffer to userland
>
>
> ...
>
> +
> +static struct page *pfm_buf_map_pagefault(struct vm_area_struct *vma,
> + unsigned long address, int *type)
> +{
> + void *kaddr;
> + struct pfm_context *ctx;
> + struct page *page;
> + size_t size;
> +
> + ctx = vma->vm_private_data;
> + if (ctx == NULL) {
> + PFM_DBG("no ctx");
> + return NOPAGE_SIGBUS;
> + }
> + size = ctx->smpl_size;
> +
> + if ( (address < (unsigned long) vma->vm_start) ||
> + (address > (unsigned long) (vma->vm_start + size)) )
>= ?
> +ssize_t __pfmk_read(struct pfm_context *ctx, union pfm_msg *msg_buf, int noblock)
> +{
> + union pfm_msg *msg;
> + ssize_t ret = 0;
> + unsigned long flags;
> +
> + /*
> + * we must masks interrupts to avoid a race condition
> + * with the PMU interrupt handler.
> + */
> + spin_lock_irqsave(&ctx->lock, flags);
> +
> + if(PFM_CTXQ_EMPTY(ctx) == 0)
> + goto fast_path;
> +
> + ret = -EAGAIN;
> + if (noblock)
> + goto empty;
> +
> + spin_unlock_irqrestore(&ctx->lock, flags);
> +
> + ret = wait_for_completion_interruptible(ctx->msgq_comp);
We do an interruptible wait, but no action is taken if the wait was
actually interrupted?
> + spin_lock_irqsave(&ctx->lock, flags);
> +
> + if(PFM_CTXQ_EMPTY(ctx))
> + goto empty;
> +
> +fast_path:
> +
> + /*
> + * extract message from queue
> + *
> + * it is possible that the message was stolen by another thread
> + * before we could protect the context after schedule()
> + */
> + msg = pfm_get_next_msg(ctx);
> + if (unlikely(msg == NULL))
> + goto empty;
> +
> + ret = sizeof(*msg);
> +
> + /*
> + * we must make a local copy before we unlock
> + * to ensure that the message queue cannot fill
> + * (overwriting our message) up before
> + * we do copy_to_user() which cannot be done
> + * with interrupts masked.
> + */
> + *msg_buf = *msg;
> +
> + PFM_DBG("type=%d ret=%zd", msg->type, ret);
> +
> +empty:
> + spin_unlock_irqrestore(&ctx->lock, flags);
> + return ret;
> +}
> +EXPORT_SYMBOL(__pfmk_read);
Can all the perfmon exports be EXPORT_SYMBOL_GPL()?
> +ssize_t __pfm_read(struct pfm_context *ctx, union pfm_msg *msg_buf, int non_block)
> +{
> + union pfm_msg *msg;
> + ssize_t ret = 0;
> + unsigned long flags;
> + DECLARE_WAITQUEUE(wait, current);
> +
> + /*
> + * we must masks interrupts to avoid a race condition
> + * with the PMU interrupt handler.
> + */
> + spin_lock_irqsave(&ctx->lock, flags);
> +
> + if(PFM_CTXQ_EMPTY(ctx) == 0)
> + goto fast_path;
> +retry:
> + /*
> + * check non-blocking read. we include it
> + * in the loop in case another thread modifies
> + * the propoerty of the file while the current thread
> + * is looping here
> + */
> +
> + ret = -EAGAIN;
whitepsace broke.
> + if(non_block)
> + goto abort_locked;
> +
> + /*
> + * put ourself on the wait queue
> + */
> + add_wait_queue(&ctx->msgq_wait, &wait);
> +
> + for (;;) {
> + /*
> + * check wait queue
> + */
> + set_current_state(TASK_INTERRUPTIBLE);
> +
> + PFM_DBG("head=%d tail=%d",
> + ctx->msgq_head,
> + ctx->msgq_tail);
> +
> + spin_unlock_irqrestore(&ctx->lock, flags);
> +
> + /*
> + * wait for message
> + */
> + schedule();
> +
> + spin_lock_irqsave(&ctx->lock, flags);
> +
> + /*
> + * check pending signals
> + */
> + ret = -ERESTARTSYS;
> + if(signal_pending(current))
> + break;
> +
> + ret = 0;
> + if(PFM_CTXQ_EMPTY(ctx) == 0)
> + break;
> + }
> +
> + set_current_state(TASK_RUNNING);
> +
> + remove_wait_queue(&ctx->msgq_wait, &wait);
> +
> + PFM_DBG("back to running ret=%zd", ret);
> +
> + if (ret < 0)
> + goto abort_locked;
> +
> +fast_path:
The above code is all a bit unidiomatic. Normally we'd do something like:
spin_lock_irqsave(&ctx->lock, flags);
while (PFM_CTXQ_EMPTY(ctx) != 0) {
prepare_to_wait(...);
spin_unlock_irqrestore(&ctx->lock, flags);
schedule();
finish_wait(...);
spin_lock_irqsave(&ctx->lock, flags);
}
> + /*
> + * extract message from queue
> + *
> + * it is possible that the message was stolen by another thread
> + * before we could protect the context after schedule()
> + */
> + msg = pfm_get_next_msg(ctx);
> + if (unlikely(msg == NULL))
> + goto retry;
> +
> + /*
> + * we must make a local copy before we unlock
> + * to ensure that the message queue cannot fill
> + * (overwriting our message) up before
> + * we do copy_to_user() which cannot be done
> + * with interrupts masked.
> + */
> + *msg_buf = *msg;
> +
> + ret = sizeof(*msg);
> +
> + PFM_DBG("type=%d size=%zu", msg->type, ret);
> +
> +abort_locked:
> + spin_unlock_irqrestore(&ctx->lock, flags);
> +
> + /*
> + * ret = EAGAIN when non-blocking and nothing is
> + * in thequeue.
> + *
> + * ret = ERESTARTSYS when signal pending
> + *
> + * otherwise ret = size of message
> + */
> + return ret;
> +}
> +
> +static ssize_t pfm_read(struct file *filp, char __user *buf, size_t size,
> + loff_t *ppos)
> +{
> + struct pfm_context *ctx;
> + union pfm_msg msg_buf;
> + int non_block, ret;
> +
> + ctx = filp->private_data;
> + if (ctx == NULL) {
> + PFM_ERR("no ctx for pfm_read");
> + return -EINVAL;
> + }
> +
> + /*
> + * cannot extract partial messages.
> + * check even when there is no message
> + *
> + * cannot extract more than one message per call. Bytes
> + * above sizeof(msg) are ignored.
> + */
> + if (size < sizeof(msg_buf)) {
> + PFM_DBG("message is too small size=%zu must be >=%zu)",
> + size,
> + sizeof(msg_buf));
> + return -EINVAL;
> + }
> +
> + non_block = filp->f_flags & O_NONBLOCK;
> +
> + ret = __pfm_read(ctx, &msg_buf, non_block);
> + if (ret > 0) {
> + if(copy_to_user(buf, &msg_buf, sizeof(msg_buf)))
> + ret = -EFAULT;
> + }
> + return ret;
> +}
> +
> +static ssize_t pfm_write(struct file *file, const char __user *ubuf,
> + size_t size, loff_t *ppos)
> +{
> + PFM_DBG("pfm_write called");
> + return -EINVAL;
> +}
> +
> +static unsigned int pfm_poll(struct file *filp, poll_table * wait)
> +{
> + struct pfm_context *ctx;
> + unsigned long flags;
> + unsigned int mask = 0;
> +
> + if (!pfm_is_fd(filp)) {
This wasn't checked in the ->read() implementation. It should be impossible?
> + PFM_ERR("pfm_poll bad magic");
> + return 0;
> + }
> +
> + ctx = filp->private_data;
> + if (ctx == NULL) {
> + PFM_ERR("pfm_poll no ctx");
> + return 0;
> + }
> +
> +
> + PFM_DBG("before poll_wait");
> +
> + poll_wait(filp, &ctx->msgq_wait, wait);
> +
> + spin_lock_irqsave(&ctx->lock, flags);
> +
> + if (PFM_CTXQ_EMPTY(ctx) == 0)
> + mask = POLLIN | POLLRDNORM;
> +
> + spin_unlock_irqrestore(&ctx->lock, flags);
Was this locking actually needed?
> + PFM_DBG("after poll_wait mask=0x%x", mask);
> +
> + return mask;
> +}
> +
>
> ...
>
> +
> +/*
> + * pfmfs should _never_ be mounted by userland - too much of security hassle,
> + * no real gain from having the whole whorehouse mounted. So we don't need
> + * any operations on the root directory. However, we need a non-trivial
> + * d_name - pfm: will go nicely and kill the special-casing in procfs.
> + */
hm, interesting.
> +static struct vfsmount *pfmfs_mnt;
> +
> +int __init init_pfm_fs(void)
> +{
> + int err = register_filesystem(&pfm_fs_type);
> + if (!err) {
> + pfmfs_mnt = kern_mount(&pfm_fs_type);
> + err = PTR_ERR(pfmfs_mnt);
> + if (IS_ERR(pfmfs_mnt))
> + unregister_filesystem(&pfm_fs_type);
> + else
> + err = 0;
> + }
> + return err;
> +}
> +
> +static void __exit exit_pfm_fs(void)
> +{
> + unregister_filesystem(&pfm_fs_type);
> + mntput(pfmfs_mnt);
> +}
<wonders whether securityfs_exit is missing a mntput>
-
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