Re: [PATCH v8 14/21] mm/mmap: Avoid zeroing vma tree in mmap_region()

[Lorenzo Stoakes <lorenzo.stoakes@oracle.com>]

On Tue, Oct 01, 2024 at 07:01:41PM GMT, Lorenzo Stoakes wrote:
> On Tue, Oct 01, 2024 at 06:43:35PM GMT, Bert Karwatzki wrote:
> [snip]
> > I applied this patch to linux-next-20240110 (it applied cleany) and got the same
> > error again (Andrew Morton asked on bugzilla me to put the logs into mails):

Hi Bert,

Could you possibly apply the below hacky patch (again using the 1st oct next
tree as a base), and share the dmesg output?

Hopefully this should give us some more information and test some theories.

Thanks, again appreciate all your help with this!

Cheers, Lorenzo

----8<----
From 36c5c148580c5aaf93f0f689c2c3de36ff62f1ba Mon Sep 17 00:00:00 2001
From: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Date: Wed, 2 Oct 2024 09:19:28 +0100
Subject: [PATCH] hack: mm: see if we can get some more information

Add some dreadful printk() hacks so we can try to get some more information
on what's going on.
---
 mm/internal.h | 15 +++++++++++++++
 mm/mmap.c     | 20 ++++++++++++++++++++
 mm/vma.c      | 11 +++++++++++
 3 files changed, 46 insertions(+)

diff --git a/mm/internal.h b/mm/internal.h
index 93083bbeeefa..cd9414b4651d 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -1443,4 +1443,19 @@ static inline void accept_page(struct page *page)
 }
 #endif /* CONFIG_UNACCEPTED_MEMORY */

+static inline bool check_interesting(unsigned long start, unsigned long end)
+{
+	const unsigned long interesting_start = 0x1740000;
+	/* Include off-by-one on purpose. */
+	const unsigned long interesting_end = 0x68000000 + 1;
+
+	/*  interesting_start            interesting_end
+	 *          |--------------------------|
+	 *           ============================> end
+	 *        <=============================   start
+	 */
+	return end > interesting_start && /* after or overlaps... */
+		start < interesting_end;  /* ...overlaps. */
+}
+
 #endif	/* __MM_INTERNAL_H */
diff --git a/mm/mmap.c b/mm/mmap.c
index dd4b35a25aeb..0ed27e558ebb 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1341,6 +1341,18 @@ struct vm_area_struct *expand_stack(struct mm_struct *mm, unsigned long addr)
 	return vma;
 }

+static void ljs_dump(struct mm_struct *mm,
+		     unsigned long addr, unsigned long len,
+		     vm_flags_t vm_flags, bool is_unmap)
+{
+	if (!check_interesting(addr, addr + len))
+		return;
+
+	pr_err("LJS: %s mm=%p [0x%lx, 0x%lx) [vm_flags=%lu]\n",
+	       is_unmap ? "munmap" : "mmap", mm, addr, addr + len,
+		vm_flags);
+}
+
 /* do_munmap() - Wrapper function for non-maple tree aware do_munmap() calls.
  * @mm: The mm_struct
  * @start: The start address to munmap
@@ -1354,6 +1366,8 @@ int do_munmap(struct mm_struct *mm, unsigned long start, size_t len,
 {
 	VMA_ITERATOR(vmi, mm, start);

+	ljs_dump(mm, start, len, 0, true);
+
 	return do_vmi_munmap(&vmi, mm, start, len, uf, false);
 }

@@ -1375,11 +1389,17 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
 	VMA_ITERATOR(vmi, mm, addr);
 	VMG_STATE(vmg, mm, &vmi, addr, end, vm_flags, pgoff);

+	ljs_dump(mm, addr, len, vm_flags, false);
+
 	vmg.file = file;
 	/* Find the first overlapping VMA */
 	vma = vma_find(&vmi, end);
 	init_vma_munmap(&vms, &vmi, vma, addr, end, uf, /* unlock = */ false);
 	if (vma) {
+		if (check_interesting(addr, addr + len))
+			pr_err("LJS: mm=%p First VMA we unmap is [%lx, %lx)\n",
+			       vma->vm_mm, vma->vm_start, vma->vm_end);
+
 		mt_init_flags(&mt_detach, vmi.mas.tree->ma_flags & MT_FLAGS_LOCK_MASK);
 		mt_on_stack(mt_detach);
 		mas_init(&mas_detach, &mt_detach, /* addr = */ 0);
diff --git a/mm/vma.c b/mm/vma.c
index 4737afcb064c..989ea3ce366d 100644
--- a/mm/vma.c
+++ b/mm/vma.c
@@ -1202,6 +1202,11 @@ int vms_gather_munmap_vmas(struct vma_munmap_struct *vms,
 			goto start_split_failed;
 		}

+		if (check_interesting(vms->vma->vm_start, vms->vma->vm_end))
+			pr_err("LJS: mm=%p vms=[%lx, %lx) split START of [%lx, %lx)\n",
+			       vms->vma->vm_mm, vms->start, vms->end,
+			       vms->vma->vm_start, vms->vma->vm_end);
+
 		error = __split_vma(vms->vmi, vms->vma, vms->start, 1);
 		if (error)
 			goto start_split_failed;
@@ -1223,6 +1228,12 @@ int vms_gather_munmap_vmas(struct vma_munmap_struct *vms,
 		}
 		/* Does it split the end? */
 		if (next->vm_end > vms->end) {
+
+			if (check_interesting(next->vm_start, next->vm_end))
+				pr_err("LJS: mm=%p vms=[%lx, %lx) split END of [%lx, %lx)\n",
+				       next->vm_mm, vms->start, vms->end,
+				       next->vm_start, next->vm_end);
+
 			error = __split_vma(vms->vmi, next, vms->end, 0);
 			if (error)
 				goto end_split_failed;
--
2.46.2