linux-kernel - Re: [PATCH v3 09/10] mm/mremap: permit mremap() move of multiple VMAs

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Message-ID: <e5a58805-e621-4628-b78d-f5d6e4b6334c@lucifer.local>
Date: Fri, 11 Jul 2025 15:14:01 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Peter Xu <peterx@...hat.com>, Alexander Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
        "Liam R . Howlett" <Liam.Howlett@...cle.com>,
        Vlastimil Babka <vbabka@...e.cz>, Jann Horn <jannh@...gle.com>,
        Pedro Falcato <pfalcato@...e.de>, Rik van Riel <riel@...riel.com>,
        linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v3 09/10] mm/mremap: permit mremap() move of multiple VMAs

Hi Andrew,

Just a quick fix-patch here to address some nits! :)

Thanks, Lorenzo

----8<----
>From 3656941531c0fb796f5a8ca7664832e58d468607 Mon Sep 17 00:00:00 2001
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Date: Fri, 11 Jul 2025 15:06:06 +0100
Subject: [PATCH] mm/mremap: address review comments

Make seen_vma a local variable, and add a comment when vmi_needs_reset is
set to explain what it's for.

Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
---
 mm/mremap.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/mm/mremap.c b/mm/mremap.c
index 59f49de0f84e..142dc5287d8a 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -69,7 +69,6 @@ struct vma_remap_struct {
 	enum mremap_type remap_type;	/* expand, shrink, etc. */
 	bool mmap_locked;		/* Is mm currently write-locked? */
 	unsigned long charged;		/* If VM_ACCOUNT, # pages to account. */
-	bool seen_vma;			/* Is >1 VMA being moved? */
 	bool vmi_needs_reset;		/* Was the VMA iterator invalidated? */
 };

@@ -1190,6 +1189,7 @@ static int copy_vma_and_data(struct vma_remap_struct *vrm,
 		*new_vma_ptr = NULL;
 		return -ENOMEM;
 	}
+	/* By merging, we may have invalidated any iterator in use. */
 	if (vma != vrm->vma)
 		vrm->vmi_needs_reset = true;

@@ -1807,10 +1807,10 @@ static unsigned long remap_move(struct vma_remap_struct *vrm)
 	unsigned long start = vrm->addr;
 	unsigned long end = vrm->addr + vrm->old_len;
 	unsigned long new_addr = vrm->new_addr;
+	bool allowed = true, seen_vma = false;
 	unsigned long target_addr = new_addr;
 	unsigned long res = -EFAULT;
 	unsigned long last_end;
-	bool allowed = true;
 	VMA_ITERATOR(vmi, current->mm, start);

 	/*
@@ -1828,7 +1828,7 @@ static unsigned long remap_move(struct vma_remap_struct *vrm)
 			return -EFAULT;

 		/* No gap permitted at the start of the range. */
-		if (!vrm->seen_vma && start < vma->vm_start)
+		if (!seen_vma && start < vma->vm_start)
 			return -EFAULT;

 		/*
@@ -1846,7 +1846,7 @@ static unsigned long remap_move(struct vma_remap_struct *vrm)
 		 *
 		 * So we map B' at A'->vm_end + X, and C' at B'->vm_end + Y.
 		 */
-		offset = vrm->seen_vma ? vma->vm_start - last_end : 0;
+		offset = seen_vma ? vma->vm_start - last_end : 0;
 		last_end = vma->vm_end;

 		vrm->vma = vma;
@@ -1855,7 +1855,7 @@ static unsigned long remap_move(struct vma_remap_struct *vrm)
 		vrm->old_len = vrm->new_len = len;

 		allowed = vma_multi_allowed(vma);
-		if (vrm->seen_vma && !allowed)
+		if (seen_vma && !allowed)
 			return -EFAULT;

 		res_vma = check_prep_vma(vrm);
@@ -1864,7 +1864,7 @@ static unsigned long remap_move(struct vma_remap_struct *vrm)
 		if (IS_ERR_VALUE(res_vma))
 			return res_vma;

-		if (!vrm->seen_vma) {
+		if (!seen_vma) {
 			VM_WARN_ON_ONCE(allowed && res_vma != new_addr);
 			res = res_vma;
 		}
@@ -1878,7 +1878,7 @@ static unsigned long remap_move(struct vma_remap_struct *vrm)
 			vma_iter_reset(&vmi);
 			vrm->vmi_needs_reset = false;
 		}
-		vrm->seen_vma = true;
+		seen_vma = true;
 		target_addr = res_vma + vrm->new_len;
 	}

--
2.50.0