There are pclusters in runtime marked with Z_EROFS_PCLUSTER_TAIL before actual I/O submission. Thus, the decompression chain can be extended if the following pcluster chain hooks such tail pcluster.

As the related comment mentioned, if some page is made of a hooked pcluster and another followed pcluster, it can be reused for in-place I/O (since I/O should be submitted anyway): _______________________________________________________________ | tail (partial) page | head (partial) page | |_____PRIMARY_HOOKED___|____________PRIMARY_FOLLOWED____________|

However, it's by no means safe to reuse as pagevec since if such PRIMARY_HOOKED pclusters finally move into bypass chain without I/O submission. It's somewhat hard to reproduce with LZ4 and I just found it (general protection fault) by ro_fsstressing a LZMA image for long time.

I'm going to actively clean up related code together with multi-page folio adaption in the next few months. Let's address it directly for easier backporting for now.

Call trace for reference: z_erofs_decompress_pcluster+0x10a/0x8a0 [erofs] z_erofs_decompress_queue.isra.36+0x3c/0x60 [erofs] z_erofs_runqueue+0x5f3/0x840 [erofs] z_erofs_readahead+0x1e8/0x320 [erofs] read_pages+0x91/0x270 page_cache_ra_unbounded+0x18b/0x240 filemap_get_pages+0x10a/0x5f0 filemap_read+0xa9/0x330 new_sync_read+0x11b/0x1a0 vfs_read+0xf1/0x190

Fixes: 3883a79abd02 ("staging: erofs: introduce VLE decompression support") Cc: stable@vger.kernel.org # 4.19+ Signed-off-by: Gao Xiang xiang@kernel.org --- changes since v1: - fix typos in commit message.

fs/erofs/zdata.c | 13 +++++++------ fs/erofs/zpvec.h | 13 ++++++++++--- 2 files changed, 17 insertions(+), 9 deletions(-)

diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c index 11c7a1aaebad..eb51df4a9f77 100644 --- a/fs/erofs/zdata.c +++ b/fs/erofs/zdata.c @@ -373,8 +373,8 @@ static bool z_erofs_try_inplace_io(struct z_erofs_collector *clt,

/* callers must be with collection lock held */ static int z_erofs_attach_page(struct z_erofs_collector *clt, - struct page *page, - enum z_erofs_page_type type) + struct page *page, enum z_erofs_page_type type, + bool pvec_safereuse) { int ret;

@@ -384,9 +384,9 @@ static int z_erofs_attach_page(struct z_erofs_collector *clt, z_erofs_try_inplace_io(clt, page)) return 0;

- ret = z_erofs_pagevec_enqueue(&clt->vector, page, type); + ret = z_erofs_pagevec_enqueue(&clt->vector, page, type, + pvec_safereuse); clt->cl->vcnt += (unsigned int)ret; - return ret ? 0 : -EAGAIN; }

@@ -729,7 +729,8 @@ static int z_erofs_do_read_page(struct z_erofs_decompress_frontend *fe, tight &= (clt->mode >= COLLECT_PRIMARY_FOLLOWED);

retry: - err = z_erofs_attach_page(clt, page, page_type); + err = z_erofs_attach_page(clt, page, page_type, + clt->mode >= COLLECT_PRIMARY_FOLLOWED); /* should allocate an additional short-lived page for pagevec */ if (err == -EAGAIN) { struct page *const newpage = @@ -737,7 +738,7 @@ static int z_erofs_do_read_page(struct z_erofs_decompress_frontend *fe,

set_page_private(newpage, Z_EROFS_SHORTLIVED_PAGE); err = z_erofs_attach_page(clt, newpage, - Z_EROFS_PAGE_TYPE_EXCLUSIVE); + Z_EROFS_PAGE_TYPE_EXCLUSIVE, true); if (!err) goto retry; } diff --git a/fs/erofs/zpvec.h b/fs/erofs/zpvec.h index dfd7fe0503bb..b05464f4a808 100644 --- a/fs/erofs/zpvec.h +++ b/fs/erofs/zpvec.h @@ -106,11 +106,18 @@ static inline void z_erofs_pagevec_ctor_init(struct z_erofs_pagevec_ctor *ctor,

static inline bool z_erofs_pagevec_enqueue(struct z_erofs_pagevec_ctor *ctor, struct page *page, - enum z_erofs_page_type type) + enum z_erofs_page_type type, + bool pvec_safereuse) { - if (!ctor->next && type) - if (ctor->index + 1 == ctor->nr) + if (!ctor->next) { + /* some pages cannot be reused as pvec safely without I/O */ + if (type == Z_EROFS_PAGE_TYPE_EXCLUSIVE && !pvec_safereuse) + type = Z_EROFS_VLE_PAGE_TYPE_TAIL_SHARED; + + if (type != Z_EROFS_PAGE_TYPE_EXCLUSIVE && + ctor->index + 1 == ctor->nr) return false; + }

if (ctor->index >= ctor->nr) z_erofs_pagevec_ctor_pagedown(ctor, false);