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From: David Howells <dhowells@redhat.com>
In-Reply-To: <750e8251-ba30-4f53-a17b-73c79e3739ce@linux.alibaba.com>
References: <750e8251-ba30-4f53-a17b-73c79e3739ce@linux.alibaba.com> <20231221132400.1601991-1-dhowells@redhat.com> <20231221132400.1601991-34-dhowells@redhat.com>
To: Gao Xiang <hsiangkao@linux.alibaba.com>
Cc: dhowells@redhat.com, Matthew Wilcox <willy@infradead.org>,
    Marc Dionne <marc.dionne@auristor.com>,
    Paulo Alcantara <pc@manguebit.com>,
    Shyam Prasad N <sprasad@microsoft.com>, Tom Talpey <tom@talpey.com>,
    Dominique Martinet <asmadeus@codewreck.org>,
    Eric Van Hensbergen <ericvh@kernel.org>,
    Ilya Dryomov <idryomov@gmail.com>,
    Christian Brauner <christian@brauner.io>, linux-cachefs@redhat.com,
    linux-afs@lists.infradead.org, linux-cifs@vger.kernel.org,
    linux-nfs@vger.kernel.org, ceph-devel@vger.kernel.org,
    v9fs@lists.linux.dev, linux-fsdevel@vger.kernel.org,
    linux-mm@kvack.org, netdev@vger.kernel.org,
    linux-kernel@vger.kernel.org, Jeff Layton <jlayton@kernel.org>,
    Steve French <smfrench@gmail.com>
Subject: Re: [PATCH v5 33/40] netfs, cachefiles: Pass upper bound length to allow expansion
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Content-ID: <198743.1704215477.1@warthog.procyon.org.uk>
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Date: Tue, 02 Jan 2024 17:11:17 +0000
Message-ID: <198744.1704215477@warthog.procyon.org.uk>

Gao Xiang <hsiangkao@linux.alibaba.com> wrote:

> >   	down =3D start - round_down(start, PAGE_SIZE);
> >   	*_start =3D start - down;
> >   	*_len =3D round_up(down + len, PAGE_SIZE);
> > +	if (down < start || *_len > upper_len)
> > +		return -ENOBUFS;
> =

> Sorry for bothering. We just found some strange when testing
> today-next EROFS over fscache.
> =

> I'm not sure the meaning of
>     if (down < start
> =

> For example, if start is page-aligned, down =3D=3D 0.
> =

> so as long as start > 0 and page-aligned, it will return
> -ENOBUFS.  Does it an intended behavior?

Yeah, I think that's wrong.

Does the attached help?

David
---

diff --git a/fs/cachefiles/io.c b/fs/cachefiles/io.c
index bffffedce4a9..7529b40bc95a 100644
--- a/fs/cachefiles/io.c
+++ b/fs/cachefiles/io.c
@@ -522,16 +522,22 @@ int __cachefiles_prepare_write(struct cachefiles_obj=
ect *object,
 			       bool no_space_allocated_yet)
 {
 	struct cachefiles_cache *cache =3D object->volume->cache;
-	loff_t start =3D *_start, pos;
-	size_t len =3D *_len, down;
+	unsigned long long start =3D *_start, pos;
+	size_t len =3D *_len;
 	int ret;
 =

 	/* Round to DIO size */
-	down =3D start - round_down(start, PAGE_SIZE);
-	*_start =3D start - down;
-	*_len =3D round_up(down + len, PAGE_SIZE);
-	if (down < start || *_len > upper_len)
+	start =3D round_down(*_start, PAGE_SIZE);
+	if (start !=3D *_start) {
+		kleave(" =3D -ENOBUFS [down]");
+		return -ENOBUFS;
+	}
+	if (*_len > upper_len) {
+		kleave(" =3D -ENOBUFS [up]");
 		return -ENOBUFS;
+	}
+
+	*_len =3D round_up(len, PAGE_SIZE);
 =

 	/* We need to work out whether there's sufficient disk space to perform
 	 * the write - but we can skip that check if we have space already
@@ -542,7 +548,7 @@ int __cachefiles_prepare_write(struct cachefiles_objec=
t *object,
 =

 	pos =3D cachefiles_inject_read_error();
 	if (pos =3D=3D 0)
-		pos =3D vfs_llseek(file, *_start, SEEK_DATA);
+		pos =3D vfs_llseek(file, start, SEEK_DATA);
 	if (pos < 0 && pos >=3D (loff_t)-MAX_ERRNO) {
 		if (pos =3D=3D -ENXIO)
 			goto check_space; /* Unallocated tail */
@@ -550,7 +556,7 @@ int __cachefiles_prepare_write(struct cachefiles_objec=
t *object,
 					  cachefiles_trace_seek_error);
 		return pos;
 	}
-	if ((u64)pos >=3D (u64)*_start + *_len)
+	if (pos >=3D start + *_len)
 		goto check_space; /* Unallocated region */
 =

 	/* We have a block that's at least partially filled - if we're low on
@@ -563,13 +569,13 @@ int __cachefiles_prepare_write(struct cachefiles_obj=
ect *object,
 =

 	pos =3D cachefiles_inject_read_error();
 	if (pos =3D=3D 0)
-		pos =3D vfs_llseek(file, *_start, SEEK_HOLE);
+		pos =3D vfs_llseek(file, start, SEEK_HOLE);
 	if (pos < 0 && pos >=3D (loff_t)-MAX_ERRNO) {
 		trace_cachefiles_io_error(object, file_inode(file), pos,
 					  cachefiles_trace_seek_error);
 		return pos;
 	}
-	if ((u64)pos >=3D (u64)*_start + *_len)
+	if (pos >=3D start + *_len)
 		return 0; /* Fully allocated */
 =

 	/* Partially allocated, but insufficient space: cull. */
@@ -577,7 +583,7 @@ int __cachefiles_prepare_write(struct cachefiles_objec=
t *object,
 	ret =3D cachefiles_inject_remove_error();
 	if (ret =3D=3D 0)
 		ret =3D vfs_fallocate(file, FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
-				    *_start, *_len);
+				    start, *_len);
 	if (ret < 0) {
 		trace_cachefiles_io_error(object, file_inode(file), ret,
 					  cachefiles_trace_fallocate_error);