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| author | Vladimir V. Saveliev <vs@namesys.com> | 2006-06-27 02:53:57 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@g5.osdl.org> | 2006-06-27 17:32:39 -0700 |
| commit | 6527c2bdf1f833cc18e8f42bd97973d583e4aa83 (patch) | |
| tree | 737055ae276cdfa75e7b3e55a3ebdd1f88105606 | |
| parent | 1c0f16e5cdff59f3b132a1b0c0d44a941f8813d2 (diff) | |
| download | linux-6527c2bdf1f833cc18e8f42bd97973d583e4aa83.tar.bz2 | |
[PATCH] generic_file_buffered_write(): deadlock on vectored write
generic_file_buffered_write() prefaults in user pages in order to avoid
deadlock on copying from the same page as write goes to.
However, it looks like there is a problem when write is vectored:
fault_in_pages_readable brings in current segment or its part (maxlen).
OTOH, filemap_copy_from_user_iovec is called to copy number of bytes
(bytes) which may exceed current segment, so filemap_copy_from_user_iovec
switches to the next segment which is not brought in yet. Pagefault is
generated. That causes the deadlock if pagefault is for the same page
write goes to: page being written is locked and not uptodate, pagefault
will deadlock trying to lock locked page.
[akpm@osdl.org: somewhat rewritten]
Cc: Neil Brown <neilb@suse.de>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
| -rw-r--r-- | mm/filemap.c | 18 |
1 files changed, 11 insertions, 7 deletions
diff --git a/mm/filemap.c b/mm/filemap.c index 9c7334bafda8..d504d6e98886 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -2095,14 +2095,21 @@ generic_file_buffered_write(struct kiocb *iocb, const struct iovec *iov, do { unsigned long index; unsigned long offset; - unsigned long maxlen; size_t copied; offset = (pos & (PAGE_CACHE_SIZE -1)); /* Within page */ index = pos >> PAGE_CACHE_SHIFT; bytes = PAGE_CACHE_SIZE - offset; - if (bytes > count) - bytes = count; + + /* Limit the size of the copy to the caller's write size */ + bytes = min(bytes, count); + + /* + * Limit the size of the copy to that of the current segment, + * because fault_in_pages_readable() doesn't know how to walk + * segments. + */ + bytes = min(bytes, cur_iov->iov_len - iov_base); /* * Bring in the user page that we will copy from _first_. @@ -2110,10 +2117,7 @@ generic_file_buffered_write(struct kiocb *iocb, const struct iovec *iov, * same page as we're writing to, without it being marked * up-to-date. */ - maxlen = cur_iov->iov_len - iov_base; - if (maxlen > bytes) - maxlen = bytes; - fault_in_pages_readable(buf, maxlen); + fault_in_pages_readable(buf, bytes); page = __grab_cache_page(mapping,index,&cached_page,&lru_pvec); if (!page) { |