Gitweb: http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=6814d7a91289ceb143285975e244a8f00fd3a830 Commit: 6814d7a91289ceb143285975e244a8f00fd3a830 Parent: 4b49643fbb3fa8bf4910f82be02d45e94e8972a4 Author: Andrew Morton <[EMAIL PROTECTED]> AuthorDate: Tue Oct 16 01:24:54 2007 -0700 Committer: Linus Torvalds <[EMAIL PROTECTED]> CommitDate: Tue Oct 16 09:42:54 2007 -0700
Revert "[PATCH] generic_file_buffered_write(): deadlock on vectored write" This reverts commit 6527c2bdf1f833cc18e8f42bd97973d583e4aa83, which fixed the following bug: When prefaulting in the pages in generic_file_buffered_write(), we only faulted in the pages for the firts segment of the iovec. If the second of successive segment described a mmapping of the page into which we're write()ing, and that page is not up-to-date, the fault handler tries to lock the already-locked page (to bring it up to date) and deadlocks. An exploit for this bug is in writev-deadlock-demo.c, in http://www.zip.com.au/~akpm/linux/patches/stuff/ext3-tools.tar.gz. (These demos assume blocksize < PAGE_CACHE_SIZE). The problem with this fix is that it takes the kernel back to doing a single prepare_write()/commit_write() per iovec segment. So in the worst case we'll run prepare_write+commit_write 1024 times where we previously would have run it once. The other problem with the fix is that it fix all the locking problems. <insert numbers obtained via ext3-tools's writev-speed.c here> And apparently this change killed NFS overwrite performance, because, I suppose, it talks to the server for each prepare_write+commit_write. So just back that patch out - we'll be fixing the deadlock by other means. Nick says: also it only ever actually papered over the bug, because after faulting in the pages, they might be unmapped or reclaimed. Signed-off-by: Nick Piggin <[EMAIL PROTECTED]> Signed-off-by: Andrew Morton <[EMAIL PROTECTED]> Signed-off-by: Linus Torvalds <[EMAIL PROTECTED]> --- mm/filemap.c | 18 +++++++----------- 1 files changed, 7 insertions(+), 11 deletions(-) diff --git a/mm/filemap.c b/mm/filemap.c index caaaa7a..4bf7d1a 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -1865,21 +1865,14 @@ 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; - - /* 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); + if (bytes > count) + bytes = count; /* * Bring in the user page that we will copy from _first_. @@ -1887,7 +1880,10 @@ 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. */ - fault_in_pages_readable(buf, bytes); + maxlen = cur_iov->iov_len - iov_base; + if (maxlen > bytes) + maxlen = bytes; + fault_in_pages_readable(buf, maxlen); page = __grab_cache_page(mapping,index,&cached_page,&lru_pvec); if (!page) { - To unsubscribe from this list: send the line "unsubscribe git-commits-head" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html