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fuse: fix race in fuse_writepages()
The patch fixes a race between ftruncate(2), mmap-ed write and write(2): 1) An user makes a page dirty via mmap-ed write. 2) The user performs shrinking truncate(2) intended to purge the page. 3) Before fuse_do_setattr calls truncate_pagecache, the page goes to writeback. fuse_writepages_fill attaches a new page to FUSE_WRITE request, then releases the original page by end_page_writeback and unlock it. 4) fuse_do_setattr completes and successfully returns. Since now, i_mutex is free. 5) Ordinary write(2) extends i_size back to cover the page. Note that fuse_send_write_pages do wait for fuse writeback, but for another page->index. 6) fuse_writepages_fill attaches more pages to the request (if any), then fuse_writepages_send is eventually called. It is supposed to crop inarg->size of the request, but it doesn't because i_size has already been extended back. Moving end_page_writeback behind fuse_writepages_send guarantees that __fuse_release_nowrite (called from fuse_do_setattr) will crop inarg->size of the request before write(2) gets the chance to extend i_size. Signed-off-by: Maxim Patlasov <mpatlasov@parallels.com> Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
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parent
26d614df1d
commit
2d033eaa00
1 changed files with 16 additions and 1 deletions
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@ -1590,6 +1590,7 @@ struct fuse_fill_wb_data {
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struct fuse_req *req;
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struct fuse_file *ff;
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struct inode *inode;
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struct page **orig_pages;
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};
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static void fuse_writepages_send(struct fuse_fill_wb_data *data)
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@ -1598,12 +1599,17 @@ static void fuse_writepages_send(struct fuse_fill_wb_data *data)
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struct inode *inode = data->inode;
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struct fuse_conn *fc = get_fuse_conn(inode);
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struct fuse_inode *fi = get_fuse_inode(inode);
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int num_pages = req->num_pages;
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int i;
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req->ff = fuse_file_get(data->ff);
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spin_lock(&fc->lock);
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list_add_tail(&req->list, &fi->queued_writes);
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fuse_flush_writepages(inode);
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spin_unlock(&fc->lock);
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for (i = 0; i < num_pages; i++)
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end_page_writeback(data->orig_pages[i]);
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}
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static int fuse_writepages_fill(struct page *page,
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@ -1684,7 +1690,7 @@ static int fuse_writepages_fill(struct page *page,
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inc_bdi_stat(page->mapping->backing_dev_info, BDI_WRITEBACK);
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inc_zone_page_state(tmp_page, NR_WRITEBACK_TEMP);
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end_page_writeback(page);
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data->orig_pages[req->num_pages] = page;
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/*
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* Protected by fc->lock against concurrent access by
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@ -1716,6 +1722,13 @@ static int fuse_writepages(struct address_space *mapping,
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data.req = NULL;
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data.ff = NULL;
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err = -ENOMEM;
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data.orig_pages = kzalloc(sizeof(struct page *) *
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FUSE_MAX_PAGES_PER_REQ,
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GFP_NOFS);
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if (!data.orig_pages)
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goto out;
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err = write_cache_pages(mapping, wbc, fuse_writepages_fill, &data);
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if (data.req) {
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/* Ignore errors if we can write at least one page */
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@ -1725,6 +1738,8 @@ static int fuse_writepages(struct address_space *mapping,
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}
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if (data.ff)
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fuse_file_put(data.ff, false);
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kfree(data.orig_pages);
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out:
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return err;
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}
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