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Subject[PATCH 2/2] fuse: wait for writeback in fuse_file_fallocate() -v2
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The patch fixes a race between mmap-ed write and fallocate(PUNCH_HOLE):

1) An user makes a page dirty via mmap-ed write.
2) The user performs fallocate(2) with mode == PUNCH_HOLE|KEEP_SIZE
and <offset, size> covering the page.
3) Before truncate_pagecache_range call from fuse_file_fallocate,
the page goes to write-back. The page is fully processed by fuse_writepage
(including end_page_writeback on the page), but fuse_flush_writepages did
nothing because fi->writectr < 0.
4) truncate_pagecache_range is called and fuse_file_fallocate is finishing
by calling fuse_release_nowrite. The latter triggers processing queued
write-back request which will write stale data to the hole soon.

Changed in v2 (thanks to Brian for suggestion):
- Do not truncate page cache until FUSE_FALLOCATE succeeded. Otherwise,
we can end up in returning -ENOTSUPP while user data is already punched
from page cache. Use filemap_write_and_wait_range() instead.

Signed-off-by: Maxim Patlasov <mpatlasov@parallels.com>
---
fs/fuse/file.c | 54 ++++++++++++++++++++++++++++++++++++++++++++++++------
1 files changed, 48 insertions(+), 6 deletions(-)

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index d1715b3..e88ba8b 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -344,6 +344,31 @@ static bool fuse_page_is_writeback(struct inode *inode, pgoff_t index)
return found;
}

+static bool fuse_range_is_writeback(struct inode *inode, pgoff_t idx_from,
+ pgoff_t idx_to)
+{
+ struct fuse_conn *fc = get_fuse_conn(inode);
+ struct fuse_inode *fi = get_fuse_inode(inode);
+ struct fuse_req *req;
+ bool found = false;
+
+ spin_lock(&fc->lock);
+ list_for_each_entry(req, &fi->writepages, writepages_entry) {
+ pgoff_t curr_index;
+
+ BUG_ON(req->inode != inode);
+ curr_index = req->misc.write.in.offset >> PAGE_CACHE_SHIFT;
+ if (!(idx_from >= curr_index + req->num_pages ||
+ idx_to < curr_index)) {
+ found = true;
+ break;
+ }
+ }
+ spin_unlock(&fc->lock);
+
+ return found;
+}
+
/*
* Wait for page writeback to be completed.
*
@@ -358,6 +383,19 @@ static int fuse_wait_on_page_writeback(struct inode *inode, pgoff_t index)
return 0;
}

+static void fuse_wait_on_writeback(struct inode *inode, pgoff_t start,
+ size_t bytes)
+{
+ struct fuse_inode *fi = get_fuse_inode(inode);
+ pgoff_t idx_from, idx_to;
+
+ idx_from = start >> PAGE_CACHE_SHIFT;
+ idx_to = (start + bytes - 1) >> PAGE_CACHE_SHIFT;
+
+ wait_event(fi->page_waitq,
+ !fuse_range_is_writeback(inode, idx_from, idx_to));
+}
+
static int fuse_flush(struct file *file, fl_owner_t id)
{
struct inode *inode = file_inode(file);
@@ -2478,8 +2516,15 @@ static long fuse_file_fallocate(struct file *file, int mode, loff_t offset,

if (lock_inode) {
mutex_lock(&inode->i_mutex);
- if (mode & FALLOC_FL_PUNCH_HOLE)
- fuse_set_nowrite(inode);
+ if (mode & FALLOC_FL_PUNCH_HOLE) {
+ loff_t endbyte = offset + length - 1;
+ err = filemap_write_and_wait_range(inode->i_mapping,
+ offset, endbyte);
+ if (err)
+ goto out;
+
+ fuse_wait_on_writeback(inode, offset, length);
+ }
}

req = fuse_get_req_nopages(fc);
@@ -2514,11 +2559,8 @@ static long fuse_file_fallocate(struct file *file, int mode, loff_t offset,
fuse_invalidate_attr(inode);

out:
- if (lock_inode) {
- if (mode & FALLOC_FL_PUNCH_HOLE)
- fuse_release_nowrite(inode);
+ if (lock_inode)
mutex_unlock(&inode->i_mutex);
- }

return err;
}


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