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SubjectRe: [BUG] problem with nfs_invalidate_page
On Wed, 29 Aug 2007 11:49:22 -0400, Trond Myklebust wrote:
>OK. I see your point... Basically, you are saying that the new
>->invalidatepage() semantics do not allow us to rely on the dirty status
>of the page in order to figure out if we need to clean up.

Exactly.

>Andrew, that was a fairly significant change in semantics...
>
>Anyhow, well done debugging it! Does the following patch fix the Oops?
>
>Trond

Yes, the patch did fix the Oops crash.
I've tested it in serveral ways, and it's working well enough so far.
Thanks!

Ryusuke Konishi


>On Tue, 2007-08-28 at 17:32 +0900, Ryusuke Konishi wrote:
>> On Mon, 27 Aug 2007 09:30:12 -0400, Trond Myklebust wrote:
>> >It looks as if ecryptfs is dropping the page lock between the calls to
>> >prepare_write() and commit_write(). That would be a bug.
>>
>> No, ecryptfs is holding the page lock between the calls to
>> nfs_prepare_write() and nfs_commit_write().
>> This is a regression since kernel 2.6.20; kernel 2.6.19 does not
>> yield the BUG.
>>
>> Please look at truncate_complete_page() and nfs_wb_page_priority()
>> which is called from nfs_invalidate_page().
>>
>> The recent truncate_complete_page() clears the dirty flag from a page
>> before calling a_ops->invalidatepage(),
>> ^^^^^^
>> static void
>> truncate_complete_page(struct address_space *mapping, struct page *page)
>> {
>> ...
>> cancel_dirty_page(page, PAGE_CACHE_SIZE); <--- Inserted here at kernel 2.6.20
>>
>> if (PagePrivate(page))
>> do_invalidatepage(page, 0); ---> will call a_ops->invalidatepage()
>> ...
>> }
>>
>> and this is disturbing nfs_wb_page_priority() from calling
>> nfs_writepage_locked() that is expected to handle the pending
>> request (=nfs_page) associated with the page.
>>
>> int nfs_wb_page_priority(struct inode *inode, struct page *page, int how)
>> {
>> ...
>> if (clear_page_dirty_for_io(page)) {
>> ret = nfs_writepage_locked(page, &wbc);
>> if (ret < 0)
>> goto out;
>> }
>> ...
>> }
>>
>> Since truncate_complete_page() will get rid of the page after
>> a_ops->invalidatepage() returns, the request (=nfs_page) associated
>> with the page becomes a garbage in nfs_inode->nfs_page_tree.
>>
>> This causes the collision of nfs_page and yields the BUG.
>>
>>
>> Cheers,
>> Ryusuke Konishi
>
>OK. I see your point... Basically, you are saying that the new
>->invalidatepage() semantics do not allow us to rely on the dirty status
>of the page in order to figure out if we need to clean up.
>
>Andrew, that was a fairly significant change in semantics...
>
>Anyhow, well done debugging it! Does the following patch fix the Oops?
>
>Trond
>
>______________________________________________________________________
>From: Trond Myklebust <Trond.Myklebust@netapp.com>
>Date: Tue, 28 Aug 2007 10:29:36 -0400
>NFS: Fix a write request leak in nfs_invalidate_page()
>Subject: No Subject
>Message-Id: <1188402562.6580.75.camel@heimdal.trondhjem.org>
>Mime-Version: 1.0
>Content-Transfer-Encoding: 7bit
>
>Ryusuke Konishi says:
>
>The recent truncate_complete_page() clears the dirty flag from a page
>before calling a_ops->invalidatepage(),
>^^^^^^
>static void
>truncate_complete_page(struct address_space *mapping, struct page *page)
>{
> ...
> cancel_dirty_page(page, PAGE_CACHE_SIZE); <--- Inserted here at
>kernel 2.6.20
>
> if (PagePrivate(page))
> do_invalidatepage(page, 0); ---> will call
>a_ops->invalidatepage()
> ...
>}
>
>and this is disturbing nfs_wb_page_priority() from calling
>nfs_writepage_locked() that is expected to handle the pending
>request (=nfs_page) associated with the page.
>
>int nfs_wb_page_priority(struct inode *inode, struct page *page, int how)
>{
> ...
> if (clear_page_dirty_for_io(page)) {
> ret = nfs_writepage_locked(page, &wbc);
> if (ret < 0)
> goto out;
> }
> ...
>}
>
>Since truncate_complete_page() will get rid of the page after
>a_ops->invalidatepage() returns, the request (=nfs_page) associated
>with the page becomes a garbage in nfs_inode->nfs_page_tree.
>------------------------
>
>Fix this by ensuring that nfs_wb_page_priority() recognises that it may
>also need to clear out non-dirty pages that have an nfs_page associated
>with them.
>
>Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
>---
>
> fs/nfs/file.c | 2 +-
> fs/nfs/write.c | 44 ++++++++++++++++++++++++++++++++++++++++++++
> include/linux/nfs_fs.h | 1 +
> 3 files changed, 46 insertions(+), 1 deletions(-)
>
>diff --git a/fs/nfs/file.c b/fs/nfs/file.c
>index c87dc71..579cf8a 100644
>--- a/fs/nfs/file.c
>+++ b/fs/nfs/file.c
>@@ -316,7 +316,7 @@ static void nfs_invalidate_page(struct page *page, unsigned long offset)
> if (offset != 0)
> return;
> /* Cancel any unstarted writes on this page */
>- nfs_wb_page_priority(page->mapping->host, page, FLUSH_INVALIDATE);
>+ nfs_wb_page_cancel(page->mapping->host, page);
> }
>
> static int nfs_release_page(struct page *page, gfp_t gfp)
>diff --git a/fs/nfs/write.c b/fs/nfs/write.c
>index ef97e0c..0d7a77c 100644
>--- a/fs/nfs/write.c
>+++ b/fs/nfs/write.c
>@@ -1396,6 +1396,50 @@ out:
> return ret;
> }
>
>+int nfs_wb_page_cancel(struct inode *inode, struct page *page)
>+{
>+ struct nfs_page *req;
>+ loff_t range_start = page_offset(page);
>+ loff_t range_end = range_start + (loff_t)(PAGE_CACHE_SIZE - 1);
>+ struct writeback_control wbc = {
>+ .bdi = page->mapping->backing_dev_info,
>+ .sync_mode = WB_SYNC_ALL,
>+ .nr_to_write = LONG_MAX,
>+ .range_start = range_start,
>+ .range_end = range_end,
>+ };
>+ int ret = 0;
>+
>+ BUG_ON(!PageLocked(page));
>+ for (;;) {
>+ req = nfs_page_find_request(page);
>+ if (req == NULL)
>+ goto out;
>+ if (test_bit(PG_NEED_COMMIT, &req->wb_flags)) {
>+ nfs_release_request(req);
>+ break;
>+ }
>+ if (nfs_lock_request_dontget(req)) {
>+ nfs_inode_remove_request(req);
>+ /*
>+ * In case nfs_inode_remove_request has marked the
>+ * page as being dirty
>+ */
>+ cancel_dirty_page(page, PAGE_CACHE_SIZE);
>+ nfs_unlock_request(req);
>+ break;
>+ }
>+ ret = nfs_wait_on_request(req);
>+ if (ret < 0)
>+ goto out;
>+ }
>+ if (!PagePrivate(page))
>+ return 0;
>+ ret = nfs_sync_mapping_wait(page->mapping, &wbc, FLUSH_INVALIDATE);
>+out:
>+ return ret;
>+}
>+
> int nfs_wb_page_priority(struct inode *inode, struct page *page, int how)
> {
> loff_t range_start = page_offset(page);
>diff --git a/include/linux/nfs_fs.h b/include/linux/nfs_fs.h
>index 157dcb0..7250eea 100644
>--- a/include/linux/nfs_fs.h
>+++ b/include/linux/nfs_fs.h
>@@ -431,6 +431,7 @@ extern int nfs_sync_mapping_range(struct address_space *, loff_t, loff_t, int);
> extern int nfs_wb_all(struct inode *inode);
> extern int nfs_wb_page(struct inode *inode, struct page* page);
> extern int nfs_wb_page_priority(struct inode *inode, struct page* page, int how);
>+extern int nfs_wb_page_cancel(struct inode *inode, struct page* page);
> #if defined(CONFIG_NFS_V3) || defined(CONFIG_NFS_V4)
> extern int nfs_commit_inode(struct inode *, int);
> extern struct nfs_write_data *nfs_commit_alloc(void);
-
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