From: Fred Isaman Subject: [PATCH 1/2] nfs: don't ignore return value from nfs_pageio_add_request Date: Wed, 19 Mar 2008 17:36:23 -0400 Message-ID: <1205962584-11369-1-git-send-email-iisaman@citi.umich.edu> Cc: linux-nfs@vger.kernel.org, Fred Isaman To: Trond Myklebust Return-path: Received: from citi.umich.edu ([141.211.133.111]:13890 "EHLO citi.umich.edu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S937815AbYCSVgZ (ORCPT ); Wed, 19 Mar 2008 17:36:25 -0400 Sender: linux-nfs-owner@vger.kernel.org List-ID: Ignoring the return value from nfs_pageio_add_request can cause deadlocks. In read path: call nfs_pageio_add_request from readpage_async_filler assume at this point that there are requests already in desc, that can't be merged with the current request. so nfs_pageio_doio is fired up to clear out desc. assume something goes wrong in setting up the io, so desc->pg_error is set. This causes nfs_pageio_add_request to return 0, *WITHOUT* adding the original request. BUT, since return code is ignored, readpage_async_filler assumes it has been added, and does nothing further, leaving page locked. do_generic_mapping_read will eventually call lock_page, resulting in deadlock In write path: page is marked dirty by generic_perform_write nfs_writepages is called call nfs_pageio_add_request from nfs_page_async_flush assume at this point that there are requests already in desc, that can't be merged with the current request. so nfs_pageio_doio is fired up to clear out desc. assume something goes wrong in setting up the io, so desc->pg_error is set. This causes nfs_page_async_flush to return 0, *WITHOUT* adding the original request, yet marking the request as locked (PG_BUSY) and in writeback, clearing dirty marks. The next time a write is done to the page, deadlock will result as nfs_write_end calls nfs_update_request Signed-off-by: Fred Isaman --- fs/nfs/read.c | 5 ++++- fs/nfs/write.c | 8 +++++++- 2 files changed, 11 insertions(+), 2 deletions(-) diff --git a/fs/nfs/read.c b/fs/nfs/read.c index 3d7d963..5a70be5 100644 --- a/fs/nfs/read.c +++ b/fs/nfs/read.c @@ -533,7 +533,10 @@ readpage_async_filler(void *data, struct page *page) if (len < PAGE_CACHE_SIZE) zero_user_segment(page, len, PAGE_CACHE_SIZE); - nfs_pageio_add_request(desc->pgio, new); + if (!nfs_pageio_add_request(desc->pgio, new)) { + error = desc->pgio->pg_error; + goto out_unlock; + } return 0; out_error: error = PTR_ERR(new); diff --git a/fs/nfs/write.c b/fs/nfs/write.c index 80c61fd..db6c17b 100644 --- a/fs/nfs/write.c +++ b/fs/nfs/write.c @@ -39,6 +39,7 @@ static struct nfs_page * nfs_update_request(struct nfs_open_context*, unsigned int, unsigned int); static void nfs_pageio_init_write(struct nfs_pageio_descriptor *desc, struct inode *inode, int ioflags); +static void nfs_redirty_request(struct nfs_page *req); static const struct rpc_call_ops nfs_write_partial_ops; static const struct rpc_call_ops nfs_write_full_ops; static const struct rpc_call_ops nfs_commit_ops; @@ -288,7 +289,12 @@ static int nfs_page_async_flush(struct nfs_pageio_descriptor *pgio, BUG(); } spin_unlock(&inode->i_lock); - nfs_pageio_add_request(pgio, req); + if (!nfs_pageio_add_request(pgio, req)) { + nfs_redirty_request(req); + nfs_end_page_writeback(req->wb_page); + nfs_clear_page_tag_locked(req); + return pgio->pg_error; + } return 0; } -- 1.5.3.3