kernel/linux.git/lib/xarray.c, branch linux-6.9.y

XArray: set the marks correctly when splitting an entry

2024-05-06T00:28:08+00:00

If we created a new node to replace an entry which had search marks set, we were setting the search mark on every entry in that node. That works fine when we're splitting to order 0, but when splitting to a larger order, we must not set the search marks on the sibling entries. Link: https://lkml.kernel.org/r/20240501153120.4094530-1-willy@infradead.org Fixes: c010d47f107f ("mm: thp: split huge page to any lower order pages") Signed-off-by: Matthew Wilcox (Oracle) Reported-by: Luis Chamberlain Link: https://lore.kernel.org/r/ZjFGCOYk3FK_zVy3@bombadil.infradead.org Tested-by: Luis Chamberlain Cc: Zi Yan Signed-off-by: Andrew Morton

xarray: Document necessary flag in alloc functions

2023-09-05T23:01:38+00:00

Adds a new line to the docstrings of functions wrapping __xa_alloc() and __xa_alloc_cyclic(), informing about the necessity of flag XA_FLAGS_ALLOC being set previously. The documentation so far says that functions wrapping __xa_alloc() and __xa_alloc_cyclic() are supposed to return either -ENOMEM or -EBUSY in case of an error. If the xarray has been initialized without the flag XA_FLAGS_ALLOC, however, they fail with a different, undocumented error code. As hinted at in Documentation/core-api/xarray.rst, wrappers around these functions should only be invoked when the flag has been set. The functions' documentation should reflect that as well. Signed-off-by: Philipp Stanner Signed-off-by: Matthew Wilcox (Oracle)

XArray: Do not return sibling entries from xa_load()

2023-07-28T19:37:45+00:00

It is possible for xa_load() to observe a sibling entry pointing to another sibling entry. An example: Thread A: Thread B: xa_store_range(xa, entry, 188, 191, gfp); xa_load(xa, 191); entry = xa_entry(xa, node, 63); [entry is a sibling of 188] xa_store_range(xa, entry, 184, 191, gfp); if (xa_is_sibling(entry)) offset = xa_to_sibling(entry); entry = xa_entry(xas->xa, node, offset); [entry is now a sibling of 184] It is sufficient to go around this loop until we hit a non-sibling entry. Sibling entries always point earlier in the node, so we are guaranteed to terminate this search. Signed-off-by: Matthew Wilcox (Oracle) Fixes: 6b24ca4a1a8d ("mm: Use multi-index entries in the page cache") Cc: stable@vger.kernel.org

radix-tree: move declarations to header

2023-06-12T18:31:50+00:00

The xarray.c file contains the only call to radix_tree_node_rcu_free(), and it comes with its own extern declaration for it. This means the function definition causes a missing-prototype warning: lib/radix-tree.c:288:6: error: no previous prototype for 'radix_tree_node_rcu_free' [-Werror=missing-prototypes] Instead, move the declaration for this function to a new header that can be included by both, and do the same for the radix_tree_node_cachep variable that has the same underlying problem but does not cause a warning with gcc. [zhangpeng.00@bytedance.com: fix building radix tree test suite] Link: https://lkml.kernel.org/r/20230521095450.21332-1-zhangpeng.00@bytedance.com Link: https://lkml.kernel.org/r/20230516194212.548910-1-arnd@kernel.org Signed-off-by: Arnd Bergmann Signed-off-by: Peng Zhang Cc: Matthew Wilcox (Oracle) Signed-off-by: Andrew Morton

mm/huge_memory: Fix xarray node memory leak

2022-06-09T20:24:25+00:00

If xas_split_alloc() fails to allocate the necessary nodes to complete the xarray entry split, it sets the xa_state to -ENOMEM, which xas_nomem() then interprets as "Please allocate more memory", not as "Please free any unnecessary memory" (which was the intended outcome). It's confusing to use xas_nomem() to free memory in this context, so call xas_destroy() instead. Reported-by: syzbot+9e27a75a8c24f3fe75c1@syzkaller.appspotmail.com Fixes: 6b24ca4a1a8d ("mm: Use multi-index entries in the page cache") Cc: stable@vger.kernel.org Signed-off-by: Matthew Wilcox (Oracle)

XArray: Disallow sibling entries of nodes

2022-04-22T19:35:40+00:00

There is a race between xas_split() and xas_load() which can result in the wrong page being returned, and thus data corruption. Fortunately, it's hard to hit (syzbot took three months to find it) and often guarded with VM_BUG_ON(). The anatomy of this race is: thread A thread B order-9 page is stored at index 0x200 lookup of page at index 0x274 page split starts load of sibling entry at offset 9 stores nodes at offsets 8-15 load of entry at offset 8 The entry at offset 8 turns out to be a node, and so we descend into it, and load the page at index 0x234 instead of 0x274. This is hard to fix on the split side; we could replace the entire node that contains the order-9 page instead of replacing the eight entries. Fixing it on the lookup side is easier; just disallow sibling entries that point to nodes. This cannot ever be a useful thing as the descent would not know the correct offset to use within the new node. The test suite continues to pass, but I have not added a new test for this bug. Reported-by: syzbot+cf4cf13056f85dec2c40@syzkaller.appspotmail.com Tested-by: syzbot+cf4cf13056f85dec2c40@syzkaller.appspotmail.com Fixes: 6b24ca4a1a8d ("mm: Use multi-index entries in the page cache") Signed-off-by: Matthew Wilcox (Oracle)

Merge tag 'xarray-5.18' of git://git.infradead.org/users/willy/xarray

2022-04-01T20:40:44+00:00

Pull XArray updates from Matthew Wilcox: - Documentation update - Fix test-suite build after move of bitmap.h - Fix xas_create_range() when a large entry is already present - Fix xas_split() of a shadow entry * tag 'xarray-5.18' of git://git.infradead.org/users/willy/xarray: XArray: Update the LRU list in xas_split() XArray: Fix xas_create_range() when multi-order entry present XArray: Include bitmap.h from xarray.h XArray: Document the locking requirement for the xa_state

XArray: Update the LRU list in xas_split()

2022-03-31T12:52:57+00:00

When splitting a value entry, we may need to add the new nodes to the LRU list and remove the parent node from the LRU list. The WARN_ON checks in shadow_lru_isolate() catch this oversight. This bug was latent until we stopped splitting folios in shrink_page_list() with commit 820c4e2e6f51 ("mm/vmscan: Free non-shmem folios without splitting them"). That allows the creation of large shadow entries, and subsequently when trying to page in a small page, we will split the large shadow entry in __filemap_add_folio(). Fixes: 8fc75643c5e1 ("XArray: add xas_split") Reported-by: Hugh Dickins Signed-off-by: Matthew Wilcox (Oracle)

XArray: Fix xas_create_range() when multi-order entry present

2022-03-28T23:25:11+00:00

If there is already an entry present that is of order >= XA_CHUNK_SHIFT when we call xas_create_range(), xas_create_range() will misinterpret that entry as a node and dereference xa_node->parent, generally leading to a crash that looks something like this: general protection fault, probably for non-canonical address 0xdffffc0000000001: 0000 [#1] PREEMPT SMP KASAN KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f] CPU: 0 PID: 32 Comm: khugepaged Not tainted 5.17.0-rc8-syzkaller-00003-g56e337f2cf13 #0 RIP: 0010:xa_parent_locked include/linux/xarray.h:1207 [inline] RIP: 0010:xas_create_range+0x2d9/0x6e0 lib/xarray.c:725 It's deterministically reproducable once you know what the problem is, but producing it in a live kernel requires khugepaged to hit a race. While the problem has been present since xas_create_range() was introduced, I'm not aware of a way to hit it before the page cache was converted to use multi-index entries. Fixes: 6b24ca4a1a8d ("mm: Use multi-index entries in the page cache") Reported-by: syzbot+0d2b0bf32ca5cfd09f2e@syzkaller.appspotmail.com Signed-off-by: Matthew Wilcox (Oracle)

xarray: use kmem_cache_alloc_lru to allocate xa_node

2022-03-22T22:57:03+00:00

The workingset will add the xa_node to the shadow_nodes list. So the allocation of xa_node should be done by kmem_cache_alloc_lru(). Using xas_set_lru() to pass the list_lru which we want to insert xa_node into to set up the xa_node reclaim context correctly. Link: https://lkml.kernel.org/r/20220228122126.37293-9-songmuchun@bytedance.com Signed-off-by: Muchun Song Acked-by: Johannes Weiner Acked-by: Roman Gushchin Cc: Alex Shi Cc: Anna Schumaker Cc: Chao Yu Cc: Dave Chinner Cc: Fam Zheng Cc: Jaegeuk Kim Cc: Kari Argillander Cc: Matthew Wilcox (Oracle) Cc: Michal Hocko Cc: Qi Zheng Cc: Shakeel Butt Cc: Theodore Ts'o Cc: Trond Myklebust Cc: Vladimir Davydov Cc: Vlastimil Babka Cc: Wei Yang Cc: Xiongchun Duan Cc: Yang Shi Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds