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

Lorenzo Stoakes
2024-10-03T11:17:58Z

On Thu, Oct 03, 2024 at 12:51:41PM +0200, Bert Karwatzki wrote:
> Here's the log procduced by this kernel:
>
> d530839eacd1 (HEAD -> maple_tree_debug) maybe fix 2
> db8adf7c0a23 hack: mm: see if we can get some more information 2
> 7e3bb072761a mm: correct error handling in mmap_region()
> 77df9e4bb222 (tag: next-20241001, origin/master, origin/HEAD, master) Add linux-next specific files for 20241001
>
> The "maybe fix 2" did not work, either.
>
[snip]

Thanks but oh man, that's disappointing. This is a really, really strange
problem.

Taking a step back, let's see if preallocation is somehow a factor here.

Please unwind all previous patches and apply this to the 1st oct next tree
- this contains fix attempts and further info.

Thanks! Lorenzo

----8<----
From 558ac3118b2861408a17993e4379f40046767fb3 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: set of fix, info stuff v3

Add some dreadful printk() hacks so we can try to get some more information
on what's going on.

Also various attempts at fixes
---
mm/internal.h | 15 +++++++++
mm/mmap.c | 91 +++++++++++++++++++++++++++++++++++++++++++++++++--
mm/vma.c | 66 ++++++++++++++++++++++++++++++++-----
3 files changed, 162 insertions(+), 10 deletions(-)

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..cef827f4e3cb 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 +1389,16 @@ 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 About to do unmaps for vms=[%lx, %lx), addr=%lx, end=%lx\n", mm, addr, addr + len, vma_iter_addr(&vmi), vma_iter_end(&vmi));
+
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);
@@ -1388,8 +1407,16 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
if (error)
goto gather_failed;

+ vma_iter_config(&vmi, addr, end);
+
vmg.next = vms.next;
vmg.prev = vms.prev;
+
+ if (check_interesting(addr, addr + len))
+ pr_err("LJS: prev=[%lx, %lx), next=[%lx, %lx)\n",
+ vmg.prev ? vmg.prev->vm_start : 0, vmg.prev ? vmg.prev->vm_end : 0,
+ vmg.next ? vmg.next->vm_start : 0, vmg.next ? vmg.next->vm_end : 0);
+
vma = NULL;
} else {
vmg.next = vma_iter_next_rewind(&vmi, &vmg.prev);
@@ -1413,9 +1440,32 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
vmg.flags = vm_flags;
}

+ if (check_interesting(addr, addr + len)) {
+ char *special = vm_flags & VM_SPECIAL ? "special" : "";
+ char *has_file = file ? "file-backed" : "";
+
+ pr_err("LJS: Interesting [%lx, %lx) flags=%lu, special=[%s] file=[%s] addr=%lx end=%lx\n",
+ addr, addr+len, vm_flags, special, has_file,
+ vma_iter_addr(&vmi), vma_iter_end(&vmi));
+ }
+
vma = vma_merge_new_range(&vmg);
- if (vma)
+ if (vma) {
+ if (check_interesting(addr, addr + len)) {
+ pr_err("LJS: Merged to [%lx, %lx), addr=%lx, end=%lx\n",
+ vma->vm_start, vma->vm_end, vma_iter_addr(&vmi),
+ vma_iter_end(&vmi));
+
+ mt_validate(&mm->mm_mt);
+
+ pr_err("LJS: Post-validate.\n");
+ }
+
goto expanded;
+ } else if (check_interesting(addr, addr + len)) {
+ pr_err("LJS: Failed to merge [%lx, %lx), reset...\n",
+ addr, addr + len);
+ }
/*
* Determine the object being mapped and call the appropriate
* specific mapper. the address has already been validated, but
@@ -1441,6 +1491,12 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
if (error)
goto unmap_and_free_vma;

+ if (check_interesting(addr, addr + len)) {
+ pr_err("LJS: call_mmap() on [%lx, %lx) old_flags=%lu new_flags=%lu new range=[%lx, %lx) [CHANGED=%s]\n",
+ addr, end, vm_flags, vma->vm_flags, vma->vm_start, vma->vm_end,
+ vm_flags != vma->vm_flags ? "YES" : "NO");
+ }
+
if (vma_is_shared_maywrite(vma)) {
error = mapping_map_writable(file->f_mapping);
if (error)
@@ -1467,6 +1523,11 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
/* If this fails, state is reset ready for a reattempt. */
merge = vma_merge_new_range(&vmg);

+ if (check_interesting(addr, addr + len))
+ pr_err("LJS: flags changed for [%lx, %lx) from %lu to %lu %s\n",
+ vma->vm_start, vma->vm_end, vm_flags, vma->vm_flags,
+ merge ? "merged" : "");
+
if (merge) {
/*
* ->mmap() can change vma->vm_file and fput
@@ -1510,10 +1571,26 @@ unsigned long mmap_region(struct file *file, unsigned long addr,

/* Lock the VMA since it is modified after insertion into VMA tree */
vma_start_write(vma);
- vma_iter_store(&vmi, vma);
+
+ if (check_interesting(addr, addr + len))
+ pr_err("LJS: mm=%p: iter store addr=%lx, end=%lx, vma=[%lx, %lx)\n",
+ mm, vma_iter_addr(&vmi), vma_iter_end(&vmi), vma->vm_start, vma->vm_end);
+
+ error = vma_iter_store_gfp(&vmi, vma, GFP_KERNEL);
+ if (error)
+ goto close_and_free_vma;
+
mm->map_count++;
vma_link_file(vma);

+ if (check_interesting(addr, addr + len)) {
+ pr_err("LJS: mm=%p: About to validate [%lx, %lx) addr=%lx, end=%lx\n",
+ mm, vma->vm_start,vma->vm_end, vma_iter_addr(&vmi), vma_iter_end(&vmi));
+
+ mt_validate(&mm->mm_mt);
+ pr_err("LJS: Post-validate.\n");
+ }
+
/*
* vma_merge_new_range() calls khugepaged_enter_vma() too, the below
* call covers the non-merge case.
@@ -1530,6 +1607,14 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
perf_event_mmap(vma);

/* Unmap any existing mapping in the area */
+
+ if (check_interesting(addr, addr + len)) {
+ pr_err("LJS: mm=%p: About to validate [%lx, %lx) addr=%lx, end=%lx\n",
+ mm, vma->vm_start,vma->vm_end, vma_iter_addr(&vmi), vma_iter_end(&vmi));
+ mt_validate(&mm->mm_mt);
+ pr_err("LJS: Post-validate.\n");
+ }
+
vms_complete_munmap_vmas(&vms, &mas_detach);

vm_stat_account(mm, vm_flags, pglen);
@@ -1594,6 +1679,8 @@ static int __vm_munmap(unsigned long start, size_t len, bool unlock)
LIST_HEAD(uf);
VMA_ITERATOR(vmi, mm, start);

+ ljs_dump(mm, start, start + len, 0, true);
+
if (mmap_write_lock_killable(mm))
return -EINTR;

diff --git a/mm/vma.c b/mm/vma.c
index 4737afcb064c..06e7a0a18aed 100644
--- a/mm/vma.c
+++ b/mm/vma.c
@@ -223,7 +223,7 @@ static void vma_complete(struct vma_prepare *vp, struct vma_iterator *vmi,
* us to insert it before dropping the locks
* (it may either follow vma or precede it).
*/
- vma_iter_store(vmi, vp->insert);
+ WARN_ON(vma_iter_store_gfp(vmi, vp->insert, GFP_KERNEL));
mm->map_count++;
}

@@ -598,22 +598,34 @@ static int commit_merge(struct vma_merge_struct *vmg,
adjust->vm_end);
}

- if (vma_iter_prealloc(vmg->vmi, vmg->vma))
- return -ENOMEM;
+// if (vma_iter_prealloc(vmg->vmi, vmg->vma))
+// return -ENOMEM;

vma_prepare(&vp);
vma_adjust_trans_huge(vmg->vma, vmg->start, vmg->end, adj_start);
vma_set_range(vmg->vma, vmg->start, vmg->end, vmg->pgoff);

- if (expanded)
- vma_iter_store(vmg->vmi, vmg->vma);
+ if (expanded) {
+ if (check_interesting(vmg->start, vmg->end)) {
+ pr_err("LJS: mm=%p expanding to [%lx, %lx) addr=%lx end=%lx\n",
+ vmg->mm, vmg->start, vmg->end,
+ vma_iter_addr(vmg->vmi), vma_iter_end(vmg->vmi));
+ }
+
+ //vma_iter_store(vmg->vmi, vmg->vma);
+ if (vma_iter_store_gfp(vmg->vmi, vmg->vma, GFP_KERNEL))
+ return -ENOMEM;
+ }

if (adj_start) {
adjust->vm_start += adj_start;
adjust->vm_pgoff += PHYS_PFN(adj_start);
if (adj_start < 0) {
WARN_ON(expanded);
- vma_iter_store(vmg->vmi, adjust);
+ //vma_iter_store(vmg->vmi, adjust);
+
+ if (vma_iter_store_gfp(vmg->vmi, adjust, GFP_KERNEL))
+ return -ENOMEM;
}
}

@@ -956,6 +968,12 @@ struct vm_area_struct *vma_merge_new_range(struct vma_merge_struct *vmg)
vma_prev(vmg->vmi); /* Equivalent to going to the previous range */
}

+ if (check_interesting(start, end)) {
+ pr_err("LJS: mm=%p About to merge [%lx, %lx) to range [%lx, %lx), addr=%lx end=%lx\n",
+ vmg->mm, start, end, vmg->start, vmg->end,
+ vma_iter_addr(vmg->vmi), vma_iter_end(vmg->vmi));
+ }
+
/*
* Now try to expand adjacent VMA(s). This takes care of removing the
* following VMA if we have VMAs on both sides.
@@ -1108,8 +1126,13 @@ void vms_clean_up_area(struct vma_munmap_struct *vms,
vms_clear_ptes(vms, mas_detach, true);
mas_set(mas_detach, 0);
mas_for_each(mas_detach, vma, ULONG_MAX)
- if (vma->vm_ops && vma->vm_ops->close)
+ if (vma->vm_ops && vma->vm_ops->close) {
+ if (check_interesting(vma->vm_start, vma->vm_end))
+ pr_err("LJS: mm=%p Closing [%lx, %lx)\n",
+ vma->vm_mm, vma->vm_start, vma->vm_end);
+
vma->vm_ops->close(vma);
+ }
vms->closed_vm_ops = true;
}

@@ -1179,6 +1202,10 @@ int vms_gather_munmap_vmas(struct vma_munmap_struct *vms,
struct vm_area_struct *next = NULL;
int error;

+ if (check_interesting(vms->vma->vm_start, vms->vma->vm_end))
+ pr_err("LJS2 vms->start=%lx, vms->vma->vm_start=%lx\n",
+ vms->start, vms->vma->vm_start);
+
/*
* If we need to split any vma, do it now to save pain later.
* Does it split the first one?
@@ -1202,6 +1229,11 @@ 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;
@@ -1217,12 +1249,24 @@ int vms_gather_munmap_vmas(struct vma_munmap_struct *vms,
for_each_vma_range(*(vms->vmi), next, vms->end) {
long nrpages;

+ if (check_interesting(vms->vma->vm_start, vms->vma->vm_end))
+ pr_err("LJS: mm=%p vms=[%lx, %lx) UNMAP [%lx, %lx) file=[%s]\n",
+ vms->vma->vm_mm, vms->start, vms->end,
+ next->vm_start, next->vm_end,
+ vms->vma->vm_file ? "file-backed" : "");
+
if (!can_modify_vma(next)) {
error = -EPERM;
goto modify_vma_failed;
}
/* 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;
@@ -1295,9 +1339,15 @@ int vms_gather_munmap_vmas(struct vma_munmap_struct *vms,
}
#endif

- while (vma_iter_addr(vms->vmi) > vms->start)
+ while (vma_iter_addr(vms->vmi) > vms->start) {
vma_iter_prev_range(vms->vmi);

+ if (check_interesting(vms->vma->vm_start, vms->vma->vm_end))
+ pr_err("LJS3: addr=%lx, end=%lx, vms->start=%lx\n",
+ vma_iter_addr(vms->vmi),
+ vma_iter_end(vms->vmi), vms->start);
+ }
+
vms->clear_ptes = true;
return 0;

--
2.46.2