mm, slub: prevent VM_BUG_ON in PageSlabPfmemalloc from ___slab_alloc

Clark Williams reported [1] a VM_BUG_ON in PageSlabPfmemalloc: page:000000009ac5dd73 refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x1ab3db flags: 0x17ffffc0000000(node=0|zone=2|lastcpupid=0x1fffff) raw: 0017ffffc0000000 ffffee1286aceb88 ffffee1287b66288 0000000000000000 raw: 0000000000000000 0000000000100000 00000000ffffffff 0000000000000000 page dumped because: VM_BUG_ON_PAGE(!PageSlab(page)) ------------[ cut here ]------------ kernel BUG at include/linux/page-flags.h:814! invalid opcode: 0000 [#1] PREEMPT_RT SMP PTI CPU: 3 PID: 12345 Comm: hackbench Not tainted 5.14.0-rc5-rt8+ #12 Hardware name: /NUC5i7RYB, BIOS RYBDWi35.86A.0359.2016.0906.1028 09/06/2016 RIP: 0010:___slab_alloc+0x340/0x940 Code: c6 48 0f a3 05 b1 7b 57 03 72 99 c7 85 78 ff ff ff ff ff ff ff 48 8b 7d 88 e9 8d fd ff ff 48 c7 c6 50 5a 7c b0 e> RSP: 0018:ffffba1c4a8b7ab0 EFLAGS: 00010293 RAX: 0000000000000000 RBX: 0000000000000002 RCX: ffff9bb765118000 RDX: 0000000000000000 RSI: ffffffffaf426050 RDI: 00000000ffffffff RBP: ffffba1c4a8b7b70 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000000 R12: ffff9bb7410d3600 R13: 0000000000400cc0 R14: 00000000001f7770 R15: ffff9bbe76df7770 FS: 00007f474b1be740(0000) GS:ffff9bbe76c00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f60c04bdaf8 CR3: 0000000124f3a003 CR4: 00000000003706e0 Call Trace: ? __alloc_skb+0x1db/0x270 ? __alloc_skb+0x1db/0x270 ? kmem_cache_alloc_node+0xa4/0x2b0 kmem_cache_alloc_node+0xa4/0x2b0 __alloc_skb+0x1db/0x270 alloc_skb_with_frags+0x64/0x250 sock_alloc_send_pskb+0x260/0x2b0 ? bpf_lsm_socket_getpeersec_dgram+0xa/0x10 unix_stream_sendmsg+0x27c/0x550 ? unix_seqpacket_recvmsg+0x60/0x60 sock_sendmsg+0xbd/0xd0 sock_write_iter+0xb9/0x120 new_sync_write+0x175/0x200 vfs_write+0x3c4/0x510 ksys_write+0xc9/0x110 do_syscall_64+0x3b/0x90 entry_SYSCALL_64_after_hwframe+0x44/0xae The problem is that we are opportunistically checking flags on a page in irq enabled section. If we are interrupted and the page is freed, it's not an issue as we detect it after disabling irqs. But on kernels with CONFIG_DEBUG_VM. The check for PageSlab flag in PageSlabPfmemalloc() can fail. Fix this by creating an "unsafe" version of the check that doesn't check PageSlab. [1] https://lore.kernel.org/lkml/[email protected]/ Link: https://lkml.kernel.org/r/[email protected] Signed-off-by: Vlastimil Babka <[email protected]> Reported-by: Clark Williams <[email protected]> Tested-by: Mike Galbraith <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Stephen Rothwell <[email protected]>
grate-driver · Aug 25, 2021 · 7455d22 · 7455d22
1 parent e9c2a5f
commit 7455d22
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diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
@@ -815,6 +815,15 @@ static inline int PageSlabPfmemalloc(struct page *page)
 	return PageActive(page);
 }
 
+/*
+ * A version of PageSlabPfmemalloc() for opportunistic checks where the page
+ * might have been freed under us and not be a PageSlab anymore.
+ */
+static inline int __PageSlabPfmemalloc(struct page *page)
+{
+	return PageActive(page);
+}
+
 static inline void SetPageSlabPfmemalloc(struct page *page)
 {
 	VM_BUG_ON_PAGE(!PageSlab(page), page);

diff --git a/mm/slub.c b/mm/slub.c
@@ -2606,6 +2606,19 @@ static inline bool pfmemalloc_match(struct page *page, gfp_t gfpflags)
 	return true;
 }
 
+/*
+ * A variant of pfmemalloc_match() that tests page flags without asserting
+ * PageSlab. Intended for opportunistic checks before taking a lock and
+ * rechecking that nobody else freed the page under us.
+ */
+static inline bool pfmemalloc_match_unsafe(struct page *page, gfp_t gfpflags)
+{
+	if (unlikely(__PageSlabPfmemalloc(page)))
+		return gfp_pfmemalloc_allowed(gfpflags);
+
+	return true;
+}
+
 /*
  * Check the page->freelist of a page and either transfer the freelist to the
  * per cpu freelist or deactivate the page.
@@ -2707,7 +2720,7 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
 	 * PFMEMALLOC but right now, we are losing the pfmemalloc
 	 * information when the page leaves the per-cpu allocator
 	 */
-	if (unlikely(!pfmemalloc_match(page, gfpflags)))
+	if (unlikely(!try_pfmemalloc_match(page, gfpflags)))
 		goto deactivate_slab;
 
 	/* must check again c->page in case IRQ handler changed it */