splice: __generic_file_splice_read: fix read/truncate race
Original patch and description from Neil Brown <neilb@suse.de>, merged and adapted to splice branch by me. Neils text follows: __generic_file_splice_read() currently samples the i_size at the start and doesn't do so again unless it needs to call ->readpage to load a page. After ->readpage it has to re-sample i_size as a truncate may have caused that page to be filled with zeros, and the read() call should not see these. However there are other activities that might cause ->readpage to be called on a page between the time that __generic_file_splice_read() samples i_size and when it finds that it has an uptodate page. These include at least read-ahead and possibly another thread performing a read So we must sample i_size *after* it has an uptodate page. Thus the current sampling at the start and after a read can be replaced with a sampling before page addition into spd. Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
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parent
475ecade68
commit
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46
fs/splice.c
46
fs/splice.c
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@ -413,37 +413,37 @@ __generic_file_splice_read(struct file *in, loff_t *ppos,
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break;
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}
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}
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fill_it:
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/*
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* i_size must be checked after PageUptodate.
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*/
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isize = i_size_read(mapping->host);
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end_index = (isize - 1) >> PAGE_CACHE_SHIFT;
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if (unlikely(!isize || index > end_index))
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break;
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/*
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* if this is the last page, see if we need to shrink
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* the length and stop
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*/
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if (end_index == index) {
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unsigned int plen;
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/*
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* i_size must be checked after ->readpage().
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* max good bytes in this page
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*/
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isize = i_size_read(mapping->host);
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end_index = (isize - 1) >> PAGE_CACHE_SHIFT;
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if (unlikely(!isize || index > end_index))
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plen = ((isize - 1) & ~PAGE_CACHE_MASK) + 1;
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if (plen <= loff)
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break;
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/*
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* if this is the last page, see if we need to shrink
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* the length and stop
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* force quit after adding this page
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*/
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if (end_index == index) {
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unsigned int plen;
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/*
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* max good bytes in this page
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*/
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plen = ((isize - 1) & ~PAGE_CACHE_MASK) + 1;
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if (plen <= loff)
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break;
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/*
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* force quit after adding this page
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*/
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this_len = min(this_len, plen - loff);
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len = this_len;
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}
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this_len = min(this_len, plen - loff);
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len = this_len;
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}
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fill_it:
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partial[page_nr].offset = loff;
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partial[page_nr].len = this_len;
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len -= this_len;
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