linux-kernel - [PATCH 08/10] guestmemfs: Block modifications when serialised

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Message-ID: <20240805093245.889357-9-jgowans@amazon.com>
Date: Mon, 5 Aug 2024 11:32:43 +0200
From: James Gowans <jgowans@...zon.com>
To: <linux-kernel@...r.kernel.org>
CC: James Gowans <jgowans@...zon.com>, Sean Christopherson
	<seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>, Alexander Viro
	<viro@...iv.linux.org.uk>, Steve Sistare <steven.sistare@...cle.com>,
	Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>, "Anthony
 Yznaga" <anthony.yznaga@...cle.com>, Mike Rapoport <rppt@...nel.org>, "Andrew
 Morton" <akpm@...ux-foundation.org>, <linux-mm@...ck.org>, Jason Gunthorpe
	<jgg@...pe.ca>, <linux-fsdevel@...r.kernel.org>, Usama Arif
	<usama.arif@...edance.com>, <kvm@...r.kernel.org>, Alexander Graf
	<graf@...zon.com>, David Woodhouse <dwmw@...zon.co.uk>, Paul Durrant
	<pdurrant@...zon.co.uk>, Nicolas Saenz Julienne <nsaenz@...zon.es>
Subject: [PATCH 08/10] guestmemfs: Block modifications when serialised

Once the memory regions for inodes, mappings and allocations have been
serialised, further modifications would break the serialised data; it
would no longer be valid.

Return an error code if attempting to create new files or allocate data
for files once serialised.

Signed-off-by: James Gowans <jgowans@...zon.com>
---
 fs/guestmemfs/file.c       | 19 ++++++++++++++++---
 fs/guestmemfs/guestmemfs.c |  1 +
 fs/guestmemfs/guestmemfs.h |  1 +
 fs/guestmemfs/inode.c      |  6 ++++++
 fs/guestmemfs/serialise.c  |  8 +++++++-
 5 files changed, 31 insertions(+), 4 deletions(-)

diff --git a/fs/guestmemfs/file.c b/fs/guestmemfs/file.c
index b1a52abcde65..8707a9d3ad90 100644
--- a/fs/guestmemfs/file.c
+++ b/fs/guestmemfs/file.c
@@ -8,19 +8,32 @@ static int truncate(struct inode *inode, loff_t newsize)
 	unsigned long free_block;
 	struct guestmemfs_inode *guestmemfs_inode;
 	unsigned long *mappings;
+	int rc = 0;
+	struct guestmemfs_sb *psb = GUESTMEMFS_PSB(inode->i_sb);
+
+	spin_lock(&psb->allocation_lock);
+
+	if (psb->serialised) {
+		rc = -EBUSY;
+		goto out;
+	}
 
 	guestmemfs_inode = guestmemfs_get_persisted_inode(inode->i_sb, inode->i_ino);
 	mappings = guestmemfs_inode->mappings;
 	i_size_write(inode, newsize);
 	for (int block_idx = 0; block_idx * PMD_SIZE < newsize; ++block_idx) {
 		free_block = guestmemfs_alloc_block(inode->i_sb);
-		if (free_block < 0)
+		if (free_block < 0) {
 			/* TODO: roll back allocations. */
-			return -ENOMEM;
+			rc = -ENOMEM;
+			goto out;
+		}
 		*(mappings + block_idx) = free_block;
 		++guestmemfs_inode->num_mappings;
 	}
-	return 0;
+out:
+	spin_unlock(&psb->allocation_lock);
+	return rc;
 }
 
 static int inode_setattr(struct mnt_idmap *idmap, struct dentry *dentry, struct iattr *iattr)
diff --git a/fs/guestmemfs/guestmemfs.c b/fs/guestmemfs/guestmemfs.c
index cf47e5100504..d854033bfb7e 100644
--- a/fs/guestmemfs/guestmemfs.c
+++ b/fs/guestmemfs/guestmemfs.c
@@ -42,6 +42,7 @@ static int guestmemfs_fill_super(struct super_block *sb, struct fs_context *fc)
 
 	if (GUESTMEMFS_PSB(sb)) {
 		pr_info("Restored super block from KHO\n");
+		GUESTMEMFS_PSB(sb)->serialised = 0;
 	} else {
 		struct guestmemfs_sb *psb;
 
diff --git a/fs/guestmemfs/guestmemfs.h b/fs/guestmemfs/guestmemfs.h
index 263d995b75ed..91cc06ae45a5 100644
--- a/fs/guestmemfs/guestmemfs.h
+++ b/fs/guestmemfs/guestmemfs.h
@@ -21,6 +21,7 @@ struct guestmemfs_sb {
 	struct guestmemfs_inode *inodes;
 	void *allocator_bitmap;
 	spinlock_t allocation_lock;
+	bool serialised;
 };
 
 // If neither of these are set the inode is not in use.
diff --git a/fs/guestmemfs/inode.c b/fs/guestmemfs/inode.c
index 61f70441d82c..d521b35d4992 100644
--- a/fs/guestmemfs/inode.c
+++ b/fs/guestmemfs/inode.c
@@ -48,6 +48,12 @@ static unsigned long guestmemfs_allocate_inode(struct super_block *sb)
 	struct guestmemfs_sb *psb = GUESTMEMFS_PSB(sb);
 
 	spin_lock(&psb->allocation_lock);
+
+	if (psb->serialised) {
+	    spin_unlock(&psb->allocation_lock);
+	    return -EBUSY;
+	}
+
 	next_free_ino = psb->next_free_ino;
 	psb->allocated_inodes += 1;
 	if (!next_free_ino)
diff --git a/fs/guestmemfs/serialise.c b/fs/guestmemfs/serialise.c
index eb70d496a3eb..347eb8049a71 100644
--- a/fs/guestmemfs/serialise.c
+++ b/fs/guestmemfs/serialise.c
@@ -111,7 +111,7 @@ int guestmemfs_serialise_to_kho(struct notifier_block *self,
 
 	switch (cmd) {
 	case KEXEC_KHO_ABORT:
-		/* No rollback action needed. */
+		GUESTMEMFS_PSB(guestmemfs_sb)->serialised = 0;
 		return NOTIFY_DONE;
 	case KEXEC_KHO_DUMP:
 		/* Handled below */
@@ -120,6 +120,7 @@ int guestmemfs_serialise_to_kho(struct notifier_block *self,
 		return NOTIFY_BAD;
 	}
 
+	spin_lock(&GUESTMEMFS_PSB(guestmemfs_sb)->allocation_lock);
 	err |= fdt_begin_node(fdt, "guestmemfs");
 	err |= fdt_property(fdt, "compatible", compatible, sizeof(compatible));
 
@@ -134,6 +135,11 @@ int guestmemfs_serialise_to_kho(struct notifier_block *self,
 
 	err |= fdt_end_node(fdt);
 
+	if (!err)
+		GUESTMEMFS_PSB(guestmemfs_sb)->serialised = 1;
+
+	spin_unlock(&GUESTMEMFS_PSB(guestmemfs_sb)->allocation_lock);
+
 	pr_info("Serialised extends [0x%llx + 0x%llx] via KHO: %i\n",
 			guestmemfs_base, guestmemfs_size, err);
 
-- 
2.34.1