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 7320272ef0074..c156460eb5587 100644 --- a/fs/smb/client/file.c +++ b/fs/smb/client/file.c @@ -2622,20 +2622,20 @@ 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);
@@ -2646,54 +2646,64 @@ 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 @@ -2710,16 +2720,12 @@ 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; }
/* @@ -2727,8 +2733,10 @@ 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; @@ -2737,17 +2745,18 @@ 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); @@ -2777,9 +2786,10 @@ 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 @@ -2799,19 +2809,18 @@ 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, @@ -2862,102 +2871,118 @@ 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; }
/* @@ -2966,7 +2991,7 @@ 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() @@ -2974,28 +2999,34 @@ 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; }