Merge tag 'notifications-pipe-prep-20191115' of git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs

Pull pipe rework from David Howells:
 "This is my set of preparatory patches for building a general
  notification queue on top of pipes. It makes a number of significant
  changes:

   - It removes the nr_exclusive argument from __wake_up_sync_key() as
     this is always 1. This prepares for the next step:

   - Adds wake_up_interruptible_sync_poll_locked() so that poll can be
     woken up from a function that's holding the poll waitqueue
     spinlock.

   - Change the pipe buffer ring to be managed in terms of unbounded
     head and tail indices rather than bounded index and length. This
     means that reading the pipe only needs to modify one index, not
     two.

   - A selection of helper functions are provided to query the state of
     the pipe buffer, plus a couple to apply updates to the pipe
     indices.

   - The pipe ring is allowed to have kernel-reserved slots. This allows
     many notification messages to be spliced in by the kernel without
     allowing userspace to pin too many pages if it writes to the same
     pipe.

   - Advance the head and tail indices inside the pipe waitqueue lock
     and use wake_up_interruptible_sync_poll_locked() to poke poll
     without having to take the lock twice.

   - Rearrange pipe_write() to preallocate the buffer it is going to
     write into and then drop the spinlock. This allows kernel
     notifications to then be added the ring whilst it is filling the
     buffer it allocated. The read side is stalled because the pipe
     mutex is still held.

   - Don't wake up readers on a pipe if there was already data in it
     when we added more.

   - Don't wake up writers on a pipe if the ring wasn't full before we
     removed a buffer"

* tag 'notifications-pipe-prep-20191115' of git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs:
  pipe: Remove sync on wake_ups
  pipe: Increase the writer-wakeup threshold to reduce context-switch count
  pipe: Check for ring full inside of the spinlock in pipe_write()
  pipe: Remove redundant wakeup from pipe_write()
  pipe: Rearrange sequence in pipe_write() to preallocate slot
  pipe: Conditionalise wakeup in pipe_read()
  pipe: Advance tail pointer inside of wait spinlock in pipe_read()
  pipe: Allow pipes to have kernel-reserved slots
  pipe: Use head and tail pointers for the ring, not cursor and length
  Add wake_up_interruptible_sync_poll_locked()
  Remove the nr_exclusive argument from __wake_up_sync_key()
  pipe: Reduce #inclusion of pipe_fs_i.h

1 files changed, 151 insertions, 118 deletions

diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index 639d5e7014c1..be2fc5793ddd 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -325,28 +325,33 @@ done:
 static bool sanity(const struct iov_iter *i)
 {
 	struct pipe_inode_info *pipe = i->pipe;
-	int idx = i->idx;
-	int next = pipe->curbuf + pipe->nrbufs;
+	unsigned int p_head = pipe->head;
+	unsigned int p_tail = pipe->tail;
+	unsigned int p_mask = pipe->ring_size - 1;
+	unsigned int p_occupancy = pipe_occupancy(p_head, p_tail);
+	unsigned int i_head = i->head;
+	unsigned int idx;
+
 	if (i->iov_offset) {
 		struct pipe_buffer *p;
-		if (unlikely(!pipe->nrbufs))
+		if (unlikely(p_occupancy == 0))
 			goto Bad;	// pipe must be non-empty
-		if (unlikely(idx != ((next - 1) & (pipe->buffers - 1))))
+		if (unlikely(i_head != p_head - 1))
 			goto Bad;	// must be at the last buffer...
 
-		p = &pipe->bufs[idx];
+		p = &pipe->bufs[i_head & p_mask];
 		if (unlikely(p->offset + p->len != i->iov_offset))
 			goto Bad;	// ... at the end of segment
 	} else {
-		if (idx != (next & (pipe->buffers - 1)))
+		if (i_head != p_head)
 			goto Bad;	// must be right after the last buffer
 	}
 	return true;
 Bad:
-	printk(KERN_ERR "idx = %d, offset = %zd\n", i->idx, i->iov_offset);
-	printk(KERN_ERR "curbuf = %d, nrbufs = %d, buffers = %d\n",
-			pipe->curbuf, pipe->nrbufs, pipe->buffers);
-	for (idx = 0; idx < pipe->buffers; idx++)
+	printk(KERN_ERR "idx = %d, offset = %zd\n", i_head, i->iov_offset);
+	printk(KERN_ERR "head = %d, tail = %d, buffers = %d\n",
+			p_head, p_tail, pipe->ring_size);
+	for (idx = 0; idx < pipe->ring_size; idx++)
 		printk(KERN_ERR "[%p %p %d %d]\n",
 			pipe->bufs[idx].ops,
 			pipe->bufs[idx].page,
@@ -359,18 +364,15 @@ Bad:
 #define sanity(i) true
 #endif
 
-static inline int next_idx(int idx, struct pipe_inode_info *pipe)
-{
-	return (idx + 1) & (pipe->buffers - 1);
-}
-
 static size_t copy_page_to_iter_pipe(struct page *page, size_t offset, size_t bytes,
 			 struct iov_iter *i)
 {
 	struct pipe_inode_info *pipe = i->pipe;
 	struct pipe_buffer *buf;
+	unsigned int p_tail = pipe->tail;
+	unsigned int p_mask = pipe->ring_size - 1;
+	unsigned int i_head = i->head;
 	size_t off;
-	int idx;
 
 	if (unlikely(bytes > i->count))
 		bytes = i->count;
@@ -382,8 +384,7 @@ static size_t copy_page_to_iter_pipe(struct page *page, size_t offset, size_t by
 		return 0;
 
 	off = i->iov_offset;
-	idx = i->idx;
-	buf = &pipe->bufs[idx];
+	buf = &pipe->bufs[i_head & p_mask];
 	if (off) {
 		if (offset == off && buf->page == page) {
 			/* merge with the last one */
@@ -391,18 +392,21 @@ static size_t copy_page_to_iter_pipe(struct page *page, size_t offset, size_t by
 			i->iov_offset += bytes;
 			goto out;
 		}
-		idx = next_idx(idx, pipe);
-		buf = &pipe->bufs[idx];
+		i_head++;
+		buf = &pipe->bufs[i_head & p_mask];
 	}
-	if (idx == pipe->curbuf && pipe->nrbufs)
+	if (pipe_full(i_head, p_tail, pipe->max_usage))
 		return 0;
-	pipe->nrbufs++;
+
 	buf->ops = &page_cache_pipe_buf_ops;
-	get_page(buf->page = page);
+	get_page(page);
+	buf->page = page;
 	buf->offset = offset;
 	buf->len = bytes;
+
+	pipe->head = i_head + 1;
 	i->iov_offset = offset + bytes;
-	i->idx = idx;
+	i->head = i_head;
 out:
 	i->count -= bytes;
 	return bytes;
@@ -480,24 +484,30 @@ static inline bool allocated(struct pipe_buffer *buf)
 	return buf->ops == &default_pipe_buf_ops;
 }
 
-static inline void data_start(const struct iov_iter *i, int *idxp, size_t *offp)
+static inline void data_start(const struct iov_iter *i,
+			      unsigned int *iter_headp, size_t *offp)
 {
+	unsigned int p_mask = i->pipe->ring_size - 1;
+	unsigned int iter_head = i->head;
 	size_t off = i->iov_offset;
-	int idx = i->idx;
-	if (off && (!allocated(&i->pipe->bufs[idx]) || off == PAGE_SIZE)) {
-		idx = next_idx(idx, i->pipe);
+
+	if (off && (!allocated(&i->pipe->bufs[iter_head & p_mask]) ||
+		    off == PAGE_SIZE)) {
+		iter_head++;
 		off = 0;
 	}
-	*idxp = idx;
+	*iter_headp = iter_head;
 	*offp = off;
 }
 
 static size_t push_pipe(struct iov_iter *i, size_t size,
-			int *idxp, size_t *offp)
+			int *iter_headp, size_t *offp)
 {
 	struct pipe_inode_info *pipe = i->pipe;
+	unsigned int p_tail = pipe->tail;
+	unsigned int p_mask = pipe->ring_size - 1;
+	unsigned int iter_head;
 	size_t off;
-	int idx;
 	ssize_t left;
 
 	if (unlikely(size > i->count))
@@ -506,33 +516,34 @@ static size_t push_pipe(struct iov_iter *i, size_t size,
 		return 0;
 
 	left = size;
-	data_start(i, &idx, &off);
-	*idxp = idx;
+	data_start(i, &iter_head, &off);
+	*iter_headp = iter_head;
 	*offp = off;
 	if (off) {
 		left -= PAGE_SIZE - off;
 		if (left <= 0) {
-			pipe->bufs[idx].len += size;
+			pipe->bufs[iter_head & p_mask].len += size;
 			return size;
 		}
-		pipe->bufs[idx].len = PAGE_SIZE;
-		idx = next_idx(idx, pipe);
+		pipe->bufs[iter_head & p_mask].len = PAGE_SIZE;
+		iter_head++;
 	}
-	while (idx != pipe->curbuf || !pipe->nrbufs) {
+	while (!pipe_full(iter_head, p_tail, pipe->max_usage)) {
+		struct pipe_buffer *buf = &pipe->bufs[iter_head & p_mask];
 		struct page *page = alloc_page(GFP_USER);
 		if (!page)
 			break;
-		pipe->nrbufs++;
-		pipe->bufs[idx].ops = &default_pipe_buf_ops;
-		pipe->bufs[idx].page = page;
-		pipe->bufs[idx].offset = 0;
-		if (left <= PAGE_SIZE) {
-			pipe->bufs[idx].len = left;
+
+		buf->ops = &default_pipe_buf_ops;
+		buf->page = page;
+		buf->offset = 0;
+		buf->len = min_t(ssize_t, left, PAGE_SIZE);
+		left -= buf->len;
+		iter_head++;
+		pipe->head = iter_head;
+
+		if (left == 0)
 			return size;
-		}
-		pipe->bufs[idx].len = PAGE_SIZE;
-		left -= PAGE_SIZE;
-		idx = next_idx(idx, pipe);
 	}
 	return size - left;
 }
@@ -541,23 +552,26 @@ static size_t copy_pipe_to_iter(const void *addr, size_t bytes,
 				struct iov_iter *i)
 {
 	struct pipe_inode_info *pipe = i->pipe;
+	unsigned int p_mask = pipe->ring_size - 1;
+	unsigned int i_head;
 	size_t n, off;
-	int idx;
 
 	if (!sanity(i))
 		return 0;
 
-	bytes = n = push_pipe(i, bytes, &idx, &off);
+	bytes = n = push_pipe(i, bytes, &i_head, &off);
 	if (unlikely(!n))
 		return 0;
-	for ( ; n; idx = next_idx(idx, pipe), off = 0) {
+	do {
 		size_t chunk = min_t(size_t, n, PAGE_SIZE - off);
-		memcpy_to_page(pipe->bufs[idx].page, off, addr, chunk);
-		i->idx = idx;
+		memcpy_to_page(pipe->bufs[i_head & p_mask].page, off, addr, chunk);
+		i->head = i_head;
 		i->iov_offset = off + chunk;
 		n -= chunk;
 		addr += chunk;
-	}
+		off = 0;
+		i_head++;
+	} while (n);
 	i->count -= bytes;
 	return bytes;
 }
@@ -573,28 +587,31 @@ static size_t csum_and_copy_to_pipe_iter(const void *addr, size_t bytes,
 				__wsum *csum, struct iov_iter *i)
 {
 	struct pipe_inode_info *pipe = i->pipe;
+	unsigned int p_mask = pipe->ring_size - 1;
+	unsigned int i_head;
 	size_t n, r;
 	size_t off = 0;
 	__wsum sum = *csum;
-	int idx;
 
 	if (!sanity(i))
 		return 0;
 
-	bytes = n = push_pipe(i, bytes, &idx, &r);
+	bytes = n = push_pipe(i, bytes, &i_head, &r);
 	if (unlikely(!n))
 		return 0;
-	for ( ; n; idx = next_idx(idx, pipe), r = 0) {
+	do {
 		size_t chunk = min_t(size_t, n, PAGE_SIZE - r);
-		char *p = kmap_atomic(pipe->bufs[idx].page);
+		char *p = kmap_atomic(pipe->bufs[i_head & p_mask].page);
 		sum = csum_and_memcpy(p + r, addr, chunk, sum, off);
 		kunmap_atomic(p);
-		i->idx = idx;
+		i->head = i_head;
 		i->iov_offset = r + chunk;
 		n -= chunk;
 		off += chunk;
 		addr += chunk;
-	}
+		r = 0;
+		i_head++;
+	} while (n);
 	i->count -= bytes;
 	*csum = sum;
 	return bytes;
@@ -645,29 +662,32 @@ static size_t copy_pipe_to_iter_mcsafe(const void *addr, size_t bytes,
 				struct iov_iter *i)
 {
 	struct pipe_inode_info *pipe = i->pipe;
+	unsigned int p_mask = pipe->ring_size - 1;
+	unsigned int i_head;
 	size_t n, off, xfer = 0;
-	int idx;
 
 	if (!sanity(i))
 		return 0;
 
-	bytes = n = push_pipe(i, bytes, &idx, &off);
+	bytes = n = push_pipe(i, bytes, &i_head, &off);
 	if (unlikely(!n))
 		return 0;
-	for ( ; n; idx = next_idx(idx, pipe), off = 0) {
+	do {
 		size_t chunk = min_t(size_t, n, PAGE_SIZE - off);
 		unsigned long rem;
 
-		rem = memcpy_mcsafe_to_page(pipe->bufs[idx].page, off, addr,
-				chunk);
-		i->idx = idx;
+		rem = memcpy_mcsafe_to_page(pipe->bufs[i_head & p_mask].page,
+					    off, addr, chunk);
+		i->head = i_head;
 		i->iov_offset = off + chunk - rem;
 		xfer += chunk - rem;
 		if (rem)
 			break;
 		n -= chunk;
 		addr += chunk;
-	}
+		off = 0;
+		i_head++;
+	} while (n);
 	i->count -= xfer;
 	return xfer;
 }
@@ -925,23 +945,26 @@ EXPORT_SYMBOL(copy_page_from_iter);
 static size_t pipe_zero(size_t bytes, struct iov_iter *i)
 {
 	struct pipe_inode_info *pipe = i->pipe;
+	unsigned int p_mask = pipe->ring_size - 1;
+	unsigned int i_head;
 	size_t n, off;
-	int idx;
 
 	if (!sanity(i))
 		return 0;
 
-	bytes = n = push_pipe(i, bytes, &idx, &off);
+	bytes = n = push_pipe(i, bytes, &i_head, &off);
 	if (unlikely(!n))
 		return 0;
 
-	for ( ; n; idx = next_idx(idx, pipe), off = 0) {
+	do {
 		size_t chunk = min_t(size_t, n, PAGE_SIZE - off);
-		memzero_page(pipe->bufs[idx].page, off, chunk);
-		i->idx = idx;
+		memzero_page(pipe->bufs[i_head & p_mask].page, off, chunk);
+		i->head = i_head;
 		i->iov_offset = off + chunk;
 		n -= chunk;
-	}
+		off = 0;
+		i_head++;
+	} while (n);
 	i->count -= bytes;
 	return bytes;
 }
@@ -987,20 +1010,26 @@ EXPORT_SYMBOL(iov_iter_copy_from_user_atomic);
 static inline void pipe_truncate(struct iov_iter *i)
 {
 	struct pipe_inode_info *pipe = i->pipe;
-	if (pipe->nrbufs) {
+	unsigned int p_tail = pipe->tail;
+	unsigned int p_head = pipe->head;
+	unsigned int p_mask = pipe->ring_size - 1;
+
+	if (!pipe_empty(p_head, p_tail)) {
+		struct pipe_buffer *buf;
+		unsigned int i_head = i->head;
 		size_t off = i->iov_offset;
-		int idx = i->idx;
-		int nrbufs = (idx - pipe->curbuf) & (pipe->buffers - 1);
+
 		if (off) {
-			pipe->bufs[idx].len = off - pipe->bufs[idx].offset;
-			idx = next_idx(idx, pipe);
-			nrbufs++;
+			buf = &pipe->bufs[i_head & p_mask];
+			buf->len = off - buf->offset;
+			i_head++;
 		}
-		while (pipe->nrbufs > nrbufs) {
-			pipe_buf_release(pipe, &pipe->bufs[idx]);
-			idx = next_idx(idx, pipe);
-			pipe->nrbufs--;
+		while (p_head != i_head) {
+			p_head--;
+			pipe_buf_release(pipe, &pipe->bufs[p_head & p_mask]);
 		}
+
+		pipe->head = p_head;
 	}
 }
 
@@ -1011,18 +1040,20 @@ static void pipe_advance(struct iov_iter *i, size_t size)
 		size = i->count;
 	if (size) {
 		struct pipe_buffer *buf;
+		unsigned int p_mask = pipe->ring_size - 1;
+		unsigned int i_head = i->head;
 		size_t off = i->iov_offset, left = size;
-		int idx = i->idx;
+
 		if (off) /* make it relative to the beginning of buffer */
-			left += off - pipe->bufs[idx].offset;
+			left += off - pipe->bufs[i_head & p_mask].offset;
 		while (1) {
-			buf = &pipe->bufs[idx];
+			buf = &pipe->bufs[i_head & p_mask];
 			if (left <= buf->len)
 				break;
 			left -= buf->len;
-			idx = next_idx(idx, pipe);
+			i_head++;
 		}
-		i->idx = idx;
+		i->head = i_head;
 		i->iov_offset = buf->offset + left;
 	}
 	i->count -= size;
@@ -1053,25 +1084,27 @@ void iov_iter_revert(struct iov_iter *i, size_t unroll)
 	i->count += unroll;
 	if (unlikely(iov_iter_is_pipe(i))) {
 		struct pipe_inode_info *pipe = i->pipe;
-		int idx = i->idx;
+		unsigned int p_mask = pipe->ring_size - 1;
+		unsigned int i_head = i->head;
 		size_t off = i->iov_offset;
 		while (1) {
-			size_t n = off - pipe->bufs[idx].offset;
+			struct pipe_buffer *b = &pipe->bufs[i_head & p_mask];
+			size_t n = off - b->offset;
 			if (unroll < n) {
 				off -= unroll;
 				break;
 			}
 			unroll -= n;
-			if (!unroll && idx == i->start_idx) {
+			if (!unroll && i_head == i->start_head) {
 				off = 0;
 				break;
 			}
-			if (!idx--)
-				idx = pipe->buffers - 1;
-			off = pipe->bufs[idx].offset + pipe->bufs[idx].len;
+			i_head--;
+			b = &pipe->bufs[i_head & p_mask];
+			off = b->offset + b->len;
 		}
 		i->iov_offset = off;
-		i->idx = idx;
+		i->head = i_head;
 		pipe_truncate(i);
 		return;
 	}
@@ -1159,13 +1192,13 @@ void iov_iter_pipe(struct iov_iter *i, unsigned int direction,
 			size_t count)
 {
 	BUG_ON(direction != READ);
-	WARN_ON(pipe->nrbufs == pipe->buffers);
+	WARN_ON(pipe_full(pipe->head, pipe->tail, pipe->ring_size));
 	i->type = ITER_PIPE | READ;
 	i->pipe = pipe;
-	i->idx = (pipe->curbuf + pipe->nrbufs) & (pipe->buffers - 1);
+	i->head = pipe->head;
 	i->iov_offset = 0;
 	i->count = count;
-	i->start_idx = i->idx;
+	i->start_head = i->head;
 }
 EXPORT_SYMBOL(iov_iter_pipe);
 
@@ -1189,11 +1222,12 @@ EXPORT_SYMBOL(iov_iter_discard);
 
 unsigned long iov_iter_alignment(const struct iov_iter *i)
 {
+	unsigned int p_mask = i->pipe->ring_size - 1;
 	unsigned long res = 0;
 	size_t size = i->count;
 
 	if (unlikely(iov_iter_is_pipe(i))) {
-		if (size && i->iov_offset && allocated(&i->pipe->bufs[i->idx]))
+		if (size && i->iov_offset && allocated(&i->pipe->bufs[i->head & p_mask]))
 			return size | i->iov_offset;
 		return size;
 	}
@@ -1231,19 +1265,20 @@ EXPORT_SYMBOL(iov_iter_gap_alignment);
 static inline ssize_t __pipe_get_pages(struct iov_iter *i,
 				size_t maxsize,
 				struct page **pages,
-				int idx,
+				int iter_head,
 				size_t *start)
 {
 	struct pipe_inode_info *pipe = i->pipe;
-	ssize_t n = push_pipe(i, maxsize, &idx, start);
+	unsigned int p_mask = pipe->ring_size - 1;
+	ssize_t n = push_pipe(i, maxsize, &iter_head, start);
 	if (!n)
 		return -EFAULT;
 
 	maxsize = n;
 	n += *start;
 	while (n > 0) {
-		get_page(*pages++ = pipe->bufs[idx].page);
-		idx = next_idx(idx, pipe);
+		get_page(*pages++ = pipe->bufs[iter_head & p_mask].page);
+		iter_head++;
 		n -= PAGE_SIZE;
 	}
 
@@ -1254,9 +1289,8 @@ static ssize_t pipe_get_pages(struct iov_iter *i,
 		   struct page **pages, size_t maxsize, unsigned maxpages,
 		   size_t *start)
 {
-	unsigned npages;
+	unsigned int iter_head, npages;
 	size_t capacity;
-	int idx;
 
 	if (!maxsize)
 		return 0;
@@ -1264,12 +1298,12 @@ static ssize_t pipe_get_pages(struct iov_iter *i,
 	if (!sanity(i))
 		return -EFAULT;
 
-	data_start(i, &idx, start);
-	/* some of this one + all after this one */
-	npages = ((i->pipe->curbuf - idx - 1) & (i->pipe->buffers - 1)) + 1;
-	capacity = min(npages,maxpages) * PAGE_SIZE - *start;
+	data_start(i, &iter_head, start);
+	/* Amount of free space: some of this one + all after this one */
+	npages = pipe_space_for_user(iter_head, i->pipe->tail, i->pipe);
+	capacity = min(npages, maxpages) * PAGE_SIZE - *start;
 
-	return __pipe_get_pages(i, min(maxsize, capacity), pages, idx, start);
+	return __pipe_get_pages(i, min(maxsize, capacity), pages, iter_head, start);
 }
 
 ssize_t iov_iter_get_pages(struct iov_iter *i,
@@ -1323,9 +1357,8 @@ static ssize_t pipe_get_pages_alloc(struct iov_iter *i,
 		   size_t *start)
 {
 	struct page **p;
+	unsigned int iter_head, npages;
 	ssize_t n;
-	int idx;
-	int npages;
 
 	if (!maxsize)
 		return 0;
@@ -1333,9 +1366,9 @@ static ssize_t pipe_get_pages_alloc(struct iov_iter *i,
 	if (!sanity(i))
 		return -EFAULT;
 
-	data_start(i, &idx, start);
-	/* some of this one + all after this one */
-	npages = ((i->pipe->curbuf - idx - 1) & (i->pipe->buffers - 1)) + 1;
+	data_start(i, &iter_head, start);
+	/* Amount of free space: some of this one + all after this one */
+	npages = pipe_space_for_user(iter_head, i->pipe->tail, i->pipe);
 	n = npages * PAGE_SIZE - *start;
 	if (maxsize > n)
 		maxsize = n;
@@ -1344,7 +1377,7 @@ static ssize_t pipe_get_pages_alloc(struct iov_iter *i,
 	p = get_pages_array(npages);
 	if (!p)
 		return -ENOMEM;
-	n = __pipe_get_pages(i, maxsize, p, idx, start);
+	n = __pipe_get_pages(i, maxsize, p, iter_head, start);
 	if (n > 0)
 		*pages = p;
 	else
@@ -1560,15 +1593,15 @@ int iov_iter_npages(const struct iov_iter *i, int maxpages)
 
 	if (unlikely(iov_iter_is_pipe(i))) {
 		struct pipe_inode_info *pipe = i->pipe;
+		unsigned int iter_head;
 		size_t off;
-		int idx;
 
 		if (!sanity(i))
 			return 0;
 
-		data_start(i, &idx, &off);
+		data_start(i, &iter_head, &off);
 		/* some of this one + all after this one */
-		npages = ((pipe->curbuf - idx - 1) & (pipe->buffers - 1)) + 1;
+		npages = pipe_space_for_user(iter_head, pipe->tail, pipe);
 		if (npages >= maxpages)
 			return maxpages;
 	} else iterate_all_kinds(i, size, v, ({