From cfdde144ae455b8612a756fe7419d57c9b7833c1 Mon Sep 17 00:00:00 2001 From: Sam Edwards Date: Sun, 25 Jan 2026 18:30:55 -0800 Subject: [PATCH] ceph: assert loop invariants in ceph_writepages_start() If `locked_pages` is zero, the page array must not be allocated: ceph_process_folio_batch() uses `locked_pages` to decide when to allocate `pages`, and redundant allocations trigger ceph_allocate_page_array()'s BUG_ON(), resulting in a worker oops (and writeback stall) or even a kernel panic. Consequently, the main loop in ceph_writepages_start() assumes that the lifetime of `pages` is confined to a single iteration. This expectation is currently not clear enough, as evidenced by the recent patch which fixed an oops caused by `pages` persisting into the next loop iteration: - "ceph: do not propagate page array emplacement errors as batch errors" Use an explicit BUG_ON() at the top of the loop to assert the loop's preexisting expectation that `pages` is cleaned up by the previous iteration. Because this is closely tied to `locked_pages`, also make it the previous iteration's responsibility to guarantee its reset, and verify with a second new BUG_ON() instead of handling (and masking) failures to do so. This patch does not change invariants, behavior, or failure modes. The added BUG_ON() lines catch conditions that would already trigger oops, but do so earlier for easier debugging and programmer clarity. Signed-off-by: Sam Edwards Reviewed-by: Ilya Dryomov Signed-off-by: Ilya Dryomov --- fs/ceph/addr.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/fs/ceph/addr.c b/fs/ceph/addr.c index daca56993390..ce09ff3e020f 100644 --- a/fs/ceph/addr.c +++ b/fs/ceph/addr.c @@ -1663,7 +1663,9 @@ retry: tag_pages_for_writeback(mapping, ceph_wbc.index, ceph_wbc.end); while (!has_writeback_done(&ceph_wbc)) { - ceph_wbc.locked_pages = 0; + BUG_ON(ceph_wbc.locked_pages); + BUG_ON(ceph_wbc.pages); + ceph_wbc.max_pages = ceph_wbc.wsize >> PAGE_SHIFT; get_more_pages: -- 2.47.3