From: Gao Xiang hsiangkao@linux.alibaba.com
[ Upstream commit 967c28b23f6c89bb8eef6a046ea88afe0d7c1029 ]
After heavily stressing EROFS with several images which include a hand-crafted image of repeated patterns for more than 46 days, I found two chains could be linked with each other almost simultaneously and form a loop so that the entire loop won't be submitted. As a consequence, the corresponding file pages will remain locked forever.
It can be _only_ observed on data-deduplicated compressed images. For example, consider two chains with five pclusters in total: Chain 1: 2->3->4->5 -- The tail pcluster is 5; Chain 2: 5->1->2 -- The tail pcluster is 2.
Chain 2 could link to Chain 1 with pcluster 5; and Chain 1 could link to Chain 2 at the same time with pcluster 2.
Since hooked chains are all linked locklessly now, I have no idea how to simply avoid the race. Instead, let's avoid hooked chains completely until I could work out a proper way to fix this and end users finally tell us that it's needed to add it back.
Actually, this optimization can be found with multi-threaded workloads (especially even more often on deduplicated compressed images), yet I'm not sure about the overall system impacts of not having this compared with implementation complexity.
Fixes: 267f2492c8f7 ("erofs: introduce multi-reference pclusters (fully-referenced)") Signed-off-by: Gao Xiang hsiangkao@linux.alibaba.com Reviewed-by: Yue Hu huyue2@coolpad.com Link: https://lore.kernel.org/r/20230526201459.128169-4-hsiangkao@linux.alibaba.co... Signed-off-by: Sasha Levin sashal@kernel.org --- fs/erofs/zdata.c | 72 ++++++++---------------------------------------- 1 file changed, 11 insertions(+), 61 deletions(-)
diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c index aaddb6781465e..92b2e4ddb7ce9 100644 --- a/fs/erofs/zdata.c +++ b/fs/erofs/zdata.c @@ -94,11 +94,8 @@ struct z_erofs_pcluster {
/* let's avoid the valid 32-bit kernel addresses */
-/* the chained workgroup has't submitted io (still open) */ +/* the end of a chain of pclusters */ #define Z_EROFS_PCLUSTER_TAIL ((void *)0x5F0ECAFE) -/* the chained workgroup has already submitted io */ -#define Z_EROFS_PCLUSTER_TAIL_CLOSED ((void *)0x5F0EDEAD) - #define Z_EROFS_PCLUSTER_NIL (NULL)
struct z_erofs_decompressqueue { @@ -375,20 +372,6 @@ int __init z_erofs_init_zip_subsystem(void)
enum z_erofs_pclustermode { Z_EROFS_PCLUSTER_INFLIGHT, - /* - * The current pclusters was the tail of an exist chain, in addition - * that the previous processed chained pclusters are all decided to - * be hooked up to it. - * A new chain will be created for the remaining pclusters which are - * not processed yet, so different from Z_EROFS_PCLUSTER_FOLLOWED, - * the next pcluster cannot reuse the whole page safely for inplace I/O - * in the following scenario: - * ________________________________________________________________ - * | tail (partial) page | head (partial) page | - * | (belongs to the next pcl) | (belongs to the current pcl) | - * |_______PCLUSTER_FOLLOWED______|________PCLUSTER_HOOKED__________| - */ - Z_EROFS_PCLUSTER_HOOKED, /* * a weak form of Z_EROFS_PCLUSTER_FOLLOWED, the difference is that it * could be dispatched into bypass queue later due to uptodated managed @@ -406,8 +389,8 @@ enum z_erofs_pclustermode { * ________________________________________________________________ * | tail (partial) page | head (partial) page | * | (of the current cl) | (of the previous collection) | - * | PCLUSTER_FOLLOWED or | | - * |_____PCLUSTER_HOOKED__|___________PCLUSTER_FOLLOWED____________| + * | | | + * |__PCLUSTER_FOLLOWED___|___________PCLUSTER_FOLLOWED____________| * * [ (*) the above page can be used as inplace I/O. ] */ @@ -420,7 +403,7 @@ struct z_erofs_decompress_frontend { struct z_erofs_bvec_iter biter;
struct page *candidate_bvpage; - struct z_erofs_pcluster *pcl, *tailpcl; + struct z_erofs_pcluster *pcl; z_erofs_next_pcluster_t owned_head; enum z_erofs_pclustermode mode;
@@ -626,19 +609,7 @@ static void z_erofs_try_to_claim_pcluster(struct z_erofs_decompress_frontend *f) return; }
- /* - * type 2, link to the end of an existing open chain, be careful - * that its submission is controlled by the original attached chain. - */ - if (*owned_head != &pcl->next && pcl != f->tailpcl && - cmpxchg(&pcl->next, Z_EROFS_PCLUSTER_TAIL, - *owned_head) == Z_EROFS_PCLUSTER_TAIL) { - *owned_head = Z_EROFS_PCLUSTER_TAIL; - f->mode = Z_EROFS_PCLUSTER_HOOKED; - f->tailpcl = NULL; - return; - } - /* type 3, it belongs to a chain, but it isn't the end of the chain */ + /* type 2, it belongs to an ongoing chain */ f->mode = Z_EROFS_PCLUSTER_INFLIGHT; }
@@ -699,9 +670,6 @@ static int z_erofs_register_pcluster(struct z_erofs_decompress_frontend *fe) goto err_out; } } - /* used to check tail merging loop due to corrupted images */ - if (fe->owned_head == Z_EROFS_PCLUSTER_TAIL) - fe->tailpcl = pcl; fe->owned_head = &pcl->next; fe->pcl = pcl; return 0; @@ -722,7 +690,6 @@ static int z_erofs_collector_begin(struct z_erofs_decompress_frontend *fe)
/* must be Z_EROFS_PCLUSTER_TAIL or pointed to previous pcluster */ DBG_BUGON(fe->owned_head == Z_EROFS_PCLUSTER_NIL); - DBG_BUGON(fe->owned_head == Z_EROFS_PCLUSTER_TAIL_CLOSED);
if (!(map->m_flags & EROFS_MAP_META)) { grp = erofs_find_workgroup(fe->inode->i_sb, @@ -741,10 +708,6 @@ static int z_erofs_collector_begin(struct z_erofs_decompress_frontend *fe)
if (ret == -EEXIST) { mutex_lock(&fe->pcl->lock); - /* used to check tail merging loop due to corrupted images */ - if (fe->owned_head == Z_EROFS_PCLUSTER_TAIL) - fe->tailpcl = fe->pcl; - z_erofs_try_to_claim_pcluster(fe); } else if (ret) { return ret; @@ -901,8 +864,7 @@ static int z_erofs_do_read_page(struct z_erofs_decompress_frontend *fe, * those chains are handled asynchronously thus the page cannot be used * for inplace I/O or bvpage (should be processed in a strict order.) */ - tight &= (fe->mode >= Z_EROFS_PCLUSTER_HOOKED && - fe->mode != Z_EROFS_PCLUSTER_FOLLOWED_NOINPLACE); + tight &= (fe->mode > Z_EROFS_PCLUSTER_FOLLOWED_NOINPLACE);
cur = end - min_t(unsigned int, offset + end - map->m_la, end); if (!(map->m_flags & EROFS_MAP_MAPPED)) { @@ -1283,10 +1245,7 @@ static void z_erofs_decompress_queue(const struct z_erofs_decompressqueue *io, }; z_erofs_next_pcluster_t owned = io->head;
- while (owned != Z_EROFS_PCLUSTER_TAIL_CLOSED) { - /* impossible that 'owned' equals Z_EROFS_WORK_TPTR_TAIL */ - DBG_BUGON(owned == Z_EROFS_PCLUSTER_TAIL); - /* impossible that 'owned' equals Z_EROFS_PCLUSTER_NIL */ + while (owned != Z_EROFS_PCLUSTER_TAIL) { DBG_BUGON(owned == Z_EROFS_PCLUSTER_NIL);
be.pcl = container_of(owned, struct z_erofs_pcluster, next); @@ -1303,7 +1262,7 @@ static void z_erofs_decompressqueue_work(struct work_struct *work) container_of(work, struct z_erofs_decompressqueue, u.work); struct page *pagepool = NULL;
- DBG_BUGON(bgq->head == Z_EROFS_PCLUSTER_TAIL_CLOSED); + DBG_BUGON(bgq->head == Z_EROFS_PCLUSTER_TAIL); z_erofs_decompress_queue(bgq, &pagepool);
erofs_release_pages(&pagepool); @@ -1465,7 +1424,7 @@ static struct z_erofs_decompressqueue *jobqueue_init(struct super_block *sb, q->sync = true; } q->sb = sb; - q->head = Z_EROFS_PCLUSTER_TAIL_CLOSED; + q->head = Z_EROFS_PCLUSTER_TAIL; return q; }
@@ -1483,11 +1442,7 @@ static void move_to_bypass_jobqueue(struct z_erofs_pcluster *pcl, z_erofs_next_pcluster_t *const submit_qtail = qtail[JQ_SUBMIT]; z_erofs_next_pcluster_t *const bypass_qtail = qtail[JQ_BYPASS];
- DBG_BUGON(owned_head == Z_EROFS_PCLUSTER_TAIL_CLOSED); - if (owned_head == Z_EROFS_PCLUSTER_TAIL) - owned_head = Z_EROFS_PCLUSTER_TAIL_CLOSED; - - WRITE_ONCE(pcl->next, Z_EROFS_PCLUSTER_TAIL_CLOSED); + WRITE_ONCE(pcl->next, Z_EROFS_PCLUSTER_TAIL);
WRITE_ONCE(*submit_qtail, owned_head); WRITE_ONCE(*bypass_qtail, &pcl->next); @@ -1558,15 +1513,10 @@ static void z_erofs_submit_queue(struct z_erofs_decompress_frontend *f, unsigned int i = 0; bool bypass = true;
- /* no possible 'owned_head' equals the following */ - DBG_BUGON(owned_head == Z_EROFS_PCLUSTER_TAIL_CLOSED); DBG_BUGON(owned_head == Z_EROFS_PCLUSTER_NIL); - pcl = container_of(owned_head, struct z_erofs_pcluster, next); + owned_head = READ_ONCE(pcl->next);
- /* close the main owned chain at first */ - owned_head = cmpxchg(&pcl->next, Z_EROFS_PCLUSTER_TAIL, - Z_EROFS_PCLUSTER_TAIL_CLOSED); if (z_erofs_is_inline_pcluster(pcl)) { move_to_bypass_jobqueue(pcl, qtail, owned_head); continue;