6.10-stable review patch. If anyone has any objections, please let me know.
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From: Gao Xiang hsiangkao@linux.alibaba.com
[ Upstream commit 9e2f9d34dd12e6e5b244ec488bcebd0c2d566c50 ]
syzbot reported a task hang issue due to a deadlock case where it is waiting for the folio lock of a cached folio that will be used for cache I/Os.
After looking into the crafted fuzzed image, I found it's formed with several overlapped big pclusters as below:
Ext: logical offset | length : physical offset | length 0: 0.. 16384 | 16384 : 151552.. 167936 | 16384 1: 16384.. 32768 | 16384 : 155648.. 172032 | 16384 2: 32768.. 49152 | 16384 : 537223168.. 537239552 | 16384 ...
Here, extent 0/1 are physically overlapped although it's entirely _impossible_ for normal filesystem images generated by mkfs.
First, managed folios containing compressed data will be marked as up-to-date and then unlocked immediately (unlike in-place folios) when compressed I/Os are complete. If physical blocks are not submitted in the incremental order, there should be separate BIOs to avoid dependency issues. However, the current code mis-arranges z_erofs_fill_bio_vec() and BIO submission which causes unexpected BIO waits.
Second, managed folios will be connected to their own pclusters for efficient inter-queries. However, this is somewhat hard to implement easily if overlapped big pclusters exist. Again, these only appear in fuzzed images so let's simply fall back to temporary short-lived pages for correctness.
Additionally, it justifies that referenced managed folios cannot be truncated for now and reverts part of commit 2080ca1ed3e4 ("erofs: tidy up `struct z_erofs_bvec`") for simplicity although it shouldn't be any difference.
Reported-by: syzbot+4fc98ed414ae63d1ada2@syzkaller.appspotmail.com Reported-by: syzbot+de04e06b28cfecf2281c@syzkaller.appspotmail.com Reported-by: syzbot+c8c8238b394be4a1087d@syzkaller.appspotmail.com Tested-by: syzbot+4fc98ed414ae63d1ada2@syzkaller.appspotmail.com Closes: https://lore.kernel.org/r/0000000000002fda01061e334873@google.com Fixes: 8e6c8fa9f2e9 ("erofs: enable big pcluster feature") Signed-off-by: Gao Xiang hsiangkao@linux.alibaba.com Link: https://lore.kernel.org/r/20240910070847.3356592-1-hsiangkao@linux.alibaba.c... Signed-off-by: Sasha Levin sashal@kernel.org --- fs/erofs/zdata.c | 71 ++++++++++++++++++++++++++---------------------- 1 file changed, 38 insertions(+), 33 deletions(-)
diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c index d269b092c477f..2535479fb82db 100644 --- a/fs/erofs/zdata.c +++ b/fs/erofs/zdata.c @@ -1416,6 +1416,7 @@ static void z_erofs_fill_bio_vec(struct bio_vec *bvec, struct z_erofs_bvec zbv; struct address_space *mapping; struct folio *folio; + struct page *page; int bs = i_blocksize(f->inode);
/* Except for inplace folios, the entire folio can be used for I/Os */ @@ -1438,7 +1439,6 @@ static void z_erofs_fill_bio_vec(struct bio_vec *bvec, * file-backed folios will be used instead. */ if (folio->private == (void *)Z_EROFS_PREALLOCATED_PAGE) { - folio->private = 0; tocache = true; goto out_tocache; } @@ -1456,7 +1456,7 @@ static void z_erofs_fill_bio_vec(struct bio_vec *bvec, }
folio_lock(folio); - if (folio->mapping == mc) { + if (likely(folio->mapping == mc)) { /* * The cached folio is still in managed cache but without * a valid `->private` pcluster hint. Let's reconnect them. @@ -1466,41 +1466,44 @@ static void z_erofs_fill_bio_vec(struct bio_vec *bvec, /* compressed_bvecs[] already takes a ref before */ folio_put(folio); } - - /* no need to submit if it is already up-to-date */ - if (folio_test_uptodate(folio)) { - folio_unlock(folio); - bvec->bv_page = NULL; + if (likely(folio->private == pcl)) { + /* don't submit cache I/Os again if already uptodate */ + if (folio_test_uptodate(folio)) { + folio_unlock(folio); + bvec->bv_page = NULL; + } + return; } - return; + /* + * Already linked with another pcluster, which only appears in + * crafted images by fuzzers for now. But handle this anyway. + */ + tocache = false; /* use temporary short-lived pages */ + } else { + DBG_BUGON(1); /* referenced managed folios can't be truncated */ + tocache = true; } - - /* - * It has been truncated, so it's unsafe to reuse this one. Let's - * allocate a new page for compressed data. - */ - DBG_BUGON(folio->mapping); - tocache = true; folio_unlock(folio); folio_put(folio); out_allocfolio: - zbv.page = erofs_allocpage(&f->pagepool, gfp | __GFP_NOFAIL); + page = erofs_allocpage(&f->pagepool, gfp | __GFP_NOFAIL); spin_lock(&pcl->obj.lockref.lock); - if (pcl->compressed_bvecs[nr].page) { - erofs_pagepool_add(&f->pagepool, zbv.page); + if (unlikely(pcl->compressed_bvecs[nr].page != zbv.page)) { + erofs_pagepool_add(&f->pagepool, page); spin_unlock(&pcl->obj.lockref.lock); cond_resched(); goto repeat; } - bvec->bv_page = pcl->compressed_bvecs[nr].page = zbv.page; - folio = page_folio(zbv.page); - /* first mark it as a temporary shortlived folio (now 1 ref) */ - folio->private = (void *)Z_EROFS_SHORTLIVED_PAGE; + bvec->bv_page = pcl->compressed_bvecs[nr].page = page; + folio = page_folio(page); spin_unlock(&pcl->obj.lockref.lock); out_tocache: if (!tocache || bs != PAGE_SIZE || - filemap_add_folio(mc, folio, pcl->obj.index + nr, gfp)) + filemap_add_folio(mc, folio, pcl->obj.index + nr, gfp)) { + /* turn into a temporary shortlived folio (1 ref) */ + folio->private = (void *)Z_EROFS_SHORTLIVED_PAGE; return; + } folio_attach_private(folio, pcl); /* drop a refcount added by allocpage (then 2 refs in total here) */ folio_put(folio); @@ -1635,13 +1638,10 @@ static void z_erofs_submit_queue(struct z_erofs_decompress_frontend *f, cur = mdev.m_pa; end = cur + pcl->pclustersize; do { - z_erofs_fill_bio_vec(&bvec, f, pcl, i++, mc); - if (!bvec.bv_page) - continue; - + bvec.bv_page = NULL; if (bio && (cur != last_pa || bio->bi_bdev != mdev.m_bdev)) { -io_retry: +drain_io: if (!erofs_is_fscache_mode(sb)) submit_bio(bio); else @@ -1654,6 +1654,15 @@ static void z_erofs_submit_queue(struct z_erofs_decompress_frontend *f, bio = NULL; }
+ if (!bvec.bv_page) { + z_erofs_fill_bio_vec(&bvec, f, pcl, i++, mc); + if (!bvec.bv_page) + continue; + if (cur + bvec.bv_len > end) + bvec.bv_len = end - cur; + DBG_BUGON(bvec.bv_len < sb->s_blocksize); + } + if (unlikely(PageWorkingset(bvec.bv_page)) && !memstall) { psi_memstall_enter(&pflags); @@ -1673,13 +1682,9 @@ static void z_erofs_submit_queue(struct z_erofs_decompress_frontend *f, ++nr_bios; }
- if (cur + bvec.bv_len > end) - bvec.bv_len = end - cur; - DBG_BUGON(bvec.bv_len < sb->s_blocksize); if (!bio_add_page(bio, bvec.bv_page, bvec.bv_len, bvec.bv_offset)) - goto io_retry; - + goto drain_io; last_pa = cur + bvec.bv_len; bypass = false; } while ((cur += bvec.bv_len) < end);