[PATCH 6.8 537/715] cifs: Fix writeback data corruption

Sasha Levin
2024-03-24T22:43:51Z

From: David Howells <dhowells@redhat.com>

[ Upstream commit f3dc1bdb6b0b0693562c7c54a6c28bafa608ba3c ]

cifs writeback doesn't correctly handle the case where
cifs_extend_writeback() hits a point where it is considering an additional
folio, but this would overrun the wsize - at which point it drops out of
the xarray scanning loop and calls xas_pause(). The problem is that
xas_pause() advances the loop counter - thereby skipping that page.

What needs to happen is for xas_reset() to be called any time we decide we
don't want to process the page we're looking at, but rather send the
request we are building and start a new one.

Fix this by copying and adapting the netfslib writepages code as a
temporary measure, with cifs writeback intending to be offloaded to
netfslib in the near future.

This also fixes the issue with the use of filemap_get_folios_tag() causing
retry of a bunch of pages which the extender already dealt with.

This can be tested by creating, say, a 64K file somewhere not on cifs
(otherwise copy-offload may get underfoot), mounting a cifs share with a
wsize of 64000, copying the file to it and then comparing the original file
and the copy:

dd if=/dev/urandom of=/tmp/64K bs=64k count=1
mount //192.168.6.1/test /mnt -o user=...,pass=...,wsize=64000
cp /tmp/64K /mnt/64K
cmp /tmp/64K /mnt/64K

Without the fix, the cmp fails at position 64000 (or shortly thereafter).

Fixes: d08089f649a0 ("cifs: Change the I/O paths to use an iterator rather than a page list")
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Steve French <sfrench@samba.org>
cc: Paulo Alcantara <pc@manguebit.com>
cc: Ronnie Sahlberg <ronniesahlberg@gmail.com>
cc: Shyam Prasad N <sprasad@microsoft.com>
cc: Tom Talpey <tom@talpey.com>
cc: Jeff Layton <jlayton@kernel.org>
cc: linux-cifs@vger.kernel.org
cc: samba-technical@lists.samba.org
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/smb/client/file.c | 283 ++++++++++++++++++++++++-------------------
1 file changed, 157 insertions(+), 126 deletions(-)

diff --git a/fs/smb/client/file.c b/fs/smb/client/file.c
index f391c9b803d84..98514f2f2d7b1 100644
--- a/fs/smb/client/file.c
+++ b/fs/smb/client/file.c
@@ -2624,20 +2624,20 @@ static int cifs_partialpagewrite(struct page *page, unsigned from, unsigned to)
* dirty pages if possible, but don't sleep while doing so.
*/
static void cifs_extend_writeback(struct address_space *mapping,
+ struct xa_state *xas,
long *_count,
loff_t start,
int max_pages,
- size_t max_len,
- unsigned int *_len)
+ loff_t max_len,
+ size_t *_len)
{
struct folio_batch batch;
struct folio *folio;
- unsigned int psize, nr_pages;
- size_t len = *_len;
- pgoff_t index = (start + len) / PAGE_SIZE;
+ unsigned int nr_pages;
+ pgoff_t index = (start + *_len) / PAGE_SIZE;
+ size_t len;
bool stop = true;
unsigned int i;
- XA_STATE(xas, &mapping->i_pages, index);

folio_batch_init(&batch);

@@ -2648,54 +2648,64 @@ static void cifs_extend_writeback(struct address_space *mapping,
*/
rcu_read_lock();

- xas_for_each(&xas, folio, ULONG_MAX) {
+ xas_for_each(xas, folio, ULONG_MAX) {
stop = true;
- if (xas_retry(&xas, folio))
+ if (xas_retry(xas, folio))
continue;
if (xa_is_value(folio))
break;
- if (folio->index != index)
+ if (folio->index != index) {
+ xas_reset(xas);
break;
+ }
+
if (!folio_try_get_rcu(folio)) {
- xas_reset(&xas);
+ xas_reset(xas);
continue;
}
nr_pages = folio_nr_pages(folio);
- if (nr_pages > max_pages)
+ if (nr_pages > max_pages) {
+ xas_reset(xas);
break;
+ }

/* Has the page moved or been split? */
- if (unlikely(folio != xas_reload(&xas))) {
+ if (unlikely(folio != xas_reload(xas))) {
folio_put(folio);
+ xas_reset(xas);
break;
}

if (!folio_trylock(folio)) {
folio_put(folio);
+ xas_reset(xas);
break;
}
- if (!folio_test_dirty(folio) || folio_test_writeback(folio)) {
+ if (!folio_test_dirty(folio) ||
+ folio_test_writeback(folio)) {
folio_unlock(folio);
folio_put(folio);
+ xas_reset(xas);
break;
}

max_pages -= nr_pages;
- psize = folio_size(folio);
- len += psize;
+ len = folio_size(folio);
stop = false;
- if (max_pages <= 0 || len >= max_len || *_count <= 0)
- stop = true;

index += nr_pages;
+ *_count -= nr_pages;
+ *_len += len;
+ if (max_pages <= 0 || *_len >= max_len || *_count <= 0)
+ stop = true;
+
if (!folio_batch_add(&batch, folio))
break;
if (stop)
break;
}

- if (!stop)
- xas_pause(&xas);
+ xas_pause(xas);
rcu_read_unlock();

/* Now, if we obtained any pages, we can shift them to being
@@ -2712,16 +2722,12 @@ static void cifs_extend_writeback(struct address_space *mapping,
if (!folio_clear_dirty_for_io(folio))
WARN_ON(1);
folio_start_writeback(folio);
-
- *_count -= folio_nr_pages(folio);
folio_unlock(folio);
}

folio_batch_release(&batch);
cond_resched();
} while (!stop);
-
- *_len = len;
}

/*
@@ -2729,8 +2735,10 @@ static void cifs_extend_writeback(struct address_space *mapping,
*/
static ssize_t cifs_write_back_from_locked_folio(struct address_space *mapping,
struct writeback_control *wbc,
+ struct xa_state *xas,
struct folio *folio,
- loff_t start, loff_t end)
+ unsigned long long start,
+ unsigned long long end)
{
struct inode *inode = mapping->host;
struct TCP_Server_Info *server;
@@ -2739,17 +2747,18 @@ static ssize_t cifs_write_back_from_locked_folio(struct address_space *mapping,
struct cifs_credits credits_on_stack;
struct cifs_credits *credits = &credits_on_stack;
struct cifsFileInfo *cfile = NULL;
- unsigned int xid, wsize, len;
- loff_t i_size = i_size_read(inode);
- size_t max_len;
+ unsigned long long i_size = i_size_read(inode), max_len;
+ unsigned int xid, wsize;
+ size_t len = folio_size(folio);
long count = wbc->nr_to_write;
int rc;

/* The folio should be locked, dirty and not undergoing writeback. */
+ if (!folio_clear_dirty_for_io(folio))
+ WARN_ON_ONCE(1);
folio_start_writeback(folio);

count -= folio_nr_pages(folio);
- len = folio_size(folio);

xid = get_xid();
server = cifs_pick_channel(cifs_sb_master_tcon(cifs_sb)->ses);
@@ -2779,9 +2788,10 @@ static ssize_t cifs_write_back_from_locked_folio(struct address_space *mapping,
wdata->server = server;
cfile = NULL;

- /* Find all consecutive lockable dirty pages, stopping when we find a
- * page that is not immediately lockable, is not dirty or is missing,
- * or we reach the end of the range.
+ /* Find all consecutive lockable dirty pages that have contiguous
+ * written regions, stopping when we find a page that is not
+ * immediately lockable, is not dirty or is missing, or we reach the
+ * end of the range.
*/
if (start < i_size) {
/* Trim the write to the EOF; the extra data is ignored. Also
@@ -2801,19 +2811,18 @@ static ssize_t cifs_write_back_from_locked_folio(struct address_space *mapping,
max_pages -= folio_nr_pages(folio);

if (max_pages > 0)
- cifs_extend_writeback(mapping, &count, start,
+ cifs_extend_writeback(mapping, xas, &count, start,
max_pages, max_len, &len);
}
- len = min_t(loff_t, len, max_len);
}
-
- wdata->bytes = len;
+ len = min_t(unsigned long long, len, i_size - start);

/* We now have a contiguous set of dirty pages, each with writeback
* set; the first page is still locked at this point, but all the rest
* have been unlocked.
*/
folio_unlock(folio);
+ wdata->bytes = len;

if (start < i_size) {
iov_iter_xarray(&wdata->iter, ITER_SOURCE, &mapping->i_pages,
@@ -2864,102 +2873,118 @@ static ssize_t cifs_write_back_from_locked_folio(struct address_space *mapping,
/*
* write a region of pages back to the server
*/
-static int cifs_writepages_region(struct address_space *mapping,
- struct writeback_control *wbc,
- loff_t start, loff_t end, loff_t *_next)
+static ssize_t cifs_writepages_begin(struct address_space *mapping,
+ struct writeback_control *wbc,
+ struct xa_state *xas,
+ unsigned long long *_start,
+ unsigned long long end)
{
- struct folio_batch fbatch;
+ struct folio *folio;
+ unsigned long long start = *_start;
+ ssize_t ret;
int skips = 0;

- folio_batch_init(&fbatch);
- do {
- int nr;
- pgoff_t index = start / PAGE_SIZE;
+search_again:
+ /* Find the first dirty page. */
+ rcu_read_lock();

- nr = filemap_get_folios_tag(mapping, &index, end / PAGE_SIZE,
- PAGECACHE_TAG_DIRTY, &fbatch);
- if (!nr)
+ for (;;) {
+ folio = xas_find_marked(xas, end / PAGE_SIZE, PAGECACHE_TAG_DIRTY);
+ if (xas_retry(xas, folio) || xa_is_value(folio))
+ continue;
+ if (!folio)
break;

- for (int i = 0; i < nr; i++) {
- ssize_t ret;
- struct folio *folio = fbatch.folios[i];
+ if (!folio_try_get_rcu(folio)) {
+ xas_reset(xas);
+ continue;
+ }

-redo_folio:
- start = folio_pos(folio); /* May regress with THPs */
+ if (unlikely(folio != xas_reload(xas))) {
+ folio_put(folio);
+ xas_reset(xas);
+ continue;
+ }

- /* At this point we hold neither the i_pages lock nor the
- * page lock: the page may be truncated or invalidated
- * (changing page->mapping to NULL), or even swizzled
- * back from swapper_space to tmpfs file mapping
- */
- if (wbc->sync_mode != WB_SYNC_NONE) {
- ret = folio_lock_killable(folio);
- if (ret < 0)
- goto write_error;
- } else {
- if (!folio_trylock(folio))
- goto skip_write;
- }
+ xas_pause(xas);
+ break;
+ }
+ rcu_read_unlock();
+ if (!folio)
+ return 0;

- if (folio->mapping != mapping ||
- !folio_test_dirty(folio)) {
- start += folio_size(folio);
- folio_unlock(folio);
- continue;
- }
+ start = folio_pos(folio); /* May regress with THPs */

- if (folio_test_writeback(folio) ||
- folio_test_fscache(folio)) {
- folio_unlock(folio);
- if (wbc->sync_mode == WB_SYNC_NONE)
- goto skip_write;
+ /* At this point we hold neither the i_pages lock nor the page lock:
+ * the page may be truncated or invalidated (changing page->mapping to
+ * NULL), or even swizzled back from swapper_space to tmpfs file
+ * mapping
+ */
+lock_again:
+ if (wbc->sync_mode != WB_SYNC_NONE) {
+ ret = folio_lock_killable(folio);
+ if (ret < 0)
+ return ret;
+ } else {
+ if (!folio_trylock(folio))
+ goto search_again;
+ }

- folio_wait_writeback(folio);
+ if (folio->mapping != mapping ||
+ !folio_test_dirty(folio)) {
+ start += folio_size(folio);
+ folio_unlock(folio);
+ goto search_again;
+ }
+
+ if (folio_test_writeback(folio) ||
+ folio_test_fscache(folio)) {
+ folio_unlock(folio);
+ if (wbc->sync_mode != WB_SYNC_NONE) {
+ folio_wait_writeback(folio);
#ifdef CONFIG_CIFS_FSCACHE
- folio_wait_fscache(folio);
+ folio_wait_fscache(folio);
#endif
- goto redo_folio;
- }
-
- if (!folio_clear_dirty_for_io(folio))
- /* We hold the page lock - it should've been dirty. */
- WARN_ON(1);
-
- ret = cifs_write_back_from_locked_folio(mapping, wbc, folio, start, end);
- if (ret < 0)
- goto write_error;
-
- start += ret;
- continue;
-
-write_error:
- folio_batch_release(&fbatch);
- *_next = start;
- return ret;
+ goto lock_again;
+ }

-skip_write:
- /*
- * Too many skipped writes, or need to reschedule?
- * Treat it as a write error without an error code.
- */
+ start += folio_size(folio);
+ if (wbc->sync_mode == WB_SYNC_NONE) {
if (skips >= 5 || need_resched()) {
ret = 0;
- goto write_error;
+ goto out;
}
-
- /* Otherwise, just skip that folio and go on to the next */
skips++;
- start += folio_size(folio);
- continue;
}
+ goto search_again;
+ }

- folio_batch_release(&fbatch);
- cond_resched();
- } while (wbc->nr_to_write > 0);
+ ret = cifs_write_back_from_locked_folio(mapping, wbc, xas, folio, start, end);
+out:
+ if (ret > 0)
+ *_start = start + ret;
+ return ret;
+}

- *_next = start;
- return 0;
+/*
+ * Write a region of pages back to the server
+ */
+static int cifs_writepages_region(struct address_space *mapping,
+ struct writeback_control *wbc,
+ unsigned long long *_start,
+ unsigned long long end)
+{
+ ssize_t ret;
+
+ XA_STATE(xas, &mapping->i_pages, *_start / PAGE_SIZE);
+
+ do {
+ ret = cifs_writepages_begin(mapping, wbc, &xas, _start, end);
+ if (ret > 0 && wbc->nr_to_write > 0)
+ cond_resched();
+ } while (ret > 0 && wbc->nr_to_write > 0);
+
+ return ret > 0 ? 0 : ret;
}

/*
@@ -2968,7 +2993,7 @@ static int cifs_writepages_region(struct address_space *mapping,
static int cifs_writepages(struct address_space *mapping,
struct writeback_control *wbc)
{
- loff_t start, next;
+ loff_t start, end;
int ret;

/* We have to be careful as we can end up racing with setattr()
@@ -2976,28 +3001,34 @@ static int cifs_writepages(struct address_space *mapping,
* to prevent it.
*/

- if (wbc->range_cyclic) {
+ if (wbc->range_cyclic && mapping->writeback_index) {
start = mapping->writeback_index * PAGE_SIZE;
- ret = cifs_writepages_region(mapping, wbc, start, LLONG_MAX, &next);
- if (ret == 0) {
- mapping->writeback_index = next / PAGE_SIZE;
- if (start > 0 && wbc->nr_to_write > 0) {
- ret = cifs_writepages_region(mapping, wbc, 0,
- start, &next);
- if (ret == 0)
- mapping->writeback_index =
- next / PAGE_SIZE;
- }
+ ret = cifs_writepages_region(mapping, wbc, &start, LLONG_MAX);
+ if (ret < 0)
+ goto out;
+
+ if (wbc->nr_to_write <= 0) {
+ mapping->writeback_index = start / PAGE_SIZE;
+ goto out;
}
+
+ start = 0;
+ end = mapping->writeback_index * PAGE_SIZE;
+ mapping->writeback_index = 0;
+ ret = cifs_writepages_region(mapping, wbc, &start, end);
+ if (ret == 0)
+ mapping->writeback_index = start / PAGE_SIZE;
} else if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX) {
- ret = cifs_writepages_region(mapping, wbc, 0, LLONG_MAX, &next);
+ start = 0;
+ ret = cifs_writepages_region(mapping, wbc, &start, LLONG_MAX);
if (wbc->nr_to_write > 0 && ret == 0)
- mapping->writeback_index = next / PAGE_SIZE;
+ mapping->writeback_index = start / PAGE_SIZE;
} else {
- ret = cifs_writepages_region(mapping, wbc,
- wbc->range_start, wbc->range_end, &next);
+ start = wbc->range_start;
+ ret = cifs_writepages_region(mapping, wbc, &start, wbc->range_end);
}

+out:
return ret;
}

--
2.43.0