There are pclusters in runtime marked with Z_EROFS_PCLUSTER_TAIL
before actual I/O submission. Thus, the submission chain can be
extended if the following pcluster chain hook 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 by ro_fsstress a LZMA image for long time.
I'm going to 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@xxxxxxxxxxxxxxx> # 4.19+
Signed-off-by: Gao Xiang <xiang@xxxxxxxxxx>
---
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);
--
2.20.1
