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author | Jens Axboe <jens.axboe@oracle.com> | 2007-06-07 07:39:42 (GMT) |
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committer | Jens Axboe <jens.axboe@oracle.com> | 2007-06-08 06:34:11 (GMT) |
commit | 620a324b744a7d66c3c45a83042f8e7fc9fc5a04 (patch) | |
tree | 07bf593206a2f38a28ba97811572d036c32b7927 | |
parent | 475ecade683566b19ebb84972de864039ac5fce3 (diff) | |
download | linux-620a324b744a7d66c3c45a83042f8e7fc9fc5a04.tar.xz |
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>
-rw-r--r-- | fs/splice.c | 46 |
1 files changed, 23 insertions, 23 deletions
diff --git a/fs/splice.c b/fs/splice.c index 123fcdb..cb21136 100644 --- a/fs/splice.c +++ b/fs/splice.c @@ -413,37 +413,37 @@ __generic_file_splice_read(struct file *in, loff_t *ppos, break; } + } +fill_it: + /* + * i_size must be checked after PageUptodate. + */ + isize = i_size_read(mapping->host); + end_index = (isize - 1) >> PAGE_CACHE_SHIFT; + if (unlikely(!isize || index > end_index)) + break; + + /* + * if this is the last page, see if we need to shrink + * the length and stop + */ + if (end_index == index) { + unsigned int plen; /* - * i_size must be checked after ->readpage(). + * max good bytes in this page */ - isize = i_size_read(mapping->host); - end_index = (isize - 1) >> PAGE_CACHE_SHIFT; - if (unlikely(!isize || index > end_index)) + plen = ((isize - 1) & ~PAGE_CACHE_MASK) + 1; + if (plen <= loff) break; /* - * if this is the last page, see if we need to shrink - * the length and stop + * force quit after adding this page */ - if (end_index == index) { - unsigned int plen; - - /* - * max good bytes in this page - */ - plen = ((isize - 1) & ~PAGE_CACHE_MASK) + 1; - if (plen <= loff) - break; - - /* - * force quit after adding this page - */ - this_len = min(this_len, plen - loff); - len = this_len; - } + this_len = min(this_len, plen - loff); + len = this_len; } -fill_it: + partial[page_nr].offset = loff; partial[page_nr].len = this_len; len -= this_len; |