Hi Miklos,
I've checked that after applying the patch, the problem no longer occurs.
Since I'm running tests on RedHat 7.7, I had to slightly modify the
patch, because on that kernel version locking around attr_version is
done differently. I'm attaching modified patch, just in case.
Best regards,
Krzysztof Rusek
On 5/18/20 3:08 PM, Miklos Szeredi wrote:
On Mon, May 4, 2020 at 1:00 PM Krzysztof Rusek <rusek@xxxxxxxxxxxxxx> wrote:
Hello,
I'm working on a user-space file system implementation utilizing fuse
kernel module (and libfuse user-space library). This file system
implementation provides a custom ioctl operation that uses
fuse_lowlevel_notify_inval_inode() function (which translates to
fuse_notify_inval_inode() in kernel) to notify the kernel that the file
was changed by the ioctl. However, under certain circumstances,
fuse_notify_inval_inode() call is ineffective, resulting in incorrect
file attributes being cached by the kernel. The problem occurs when
ioctl() is executed in parallel with getattr().
I noticed this problem on RedHat 7.7 (3.10.0-1062.el7.x86_64), but I
believe mainline kernel is affected as well.
I think there is a bug in the way fuse_notify_inval_inode() invalidates
file attributes. If getattr() started before fuse_notify_inval_inode()
was called, then the attributes returned by user-space process may be
out of date, and should not be cached. But fuse_notify_inval_inode()
only clears attribute validity time, which does not prevent getattr()
result from being cached.
More precisely, this bug occurs in the following scenario:
1. kernel starts handling ioctl
2. file system process receives ioctl request
3. kernel starts handling getattr
4. file system process receives getattr request
5. file system process executes getattr
6. file system process executes ioctl, changing file state
7. file system process invokes fuse_lowlevel_notify_inval_inode(), which
invalidates file attributes in kernel
8. file system process sends ioctl reply, ioctl handling ends
9. file system process sends getattr reply, attributes are incorrectly
cached in the kernel
(Note that this scenario assumes that file system implementation is
multi-threaded, therefore allowing ioctl() and getattr() to be handled
in parallel.)
Can you please try the attached patch?
Thanks,
Miklos
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -332,6 +332,8 @@ struct inode *fuse_iget(struct super_block *sb, u64 nodeid,
int fuse_reverse_inval_inode(struct super_block *sb, u64 nodeid,
loff_t offset, loff_t len)
{
+ struct fuse_conn *fc = get_fuse_conn_super(sb);
+ struct fuse_inode *fi;
struct inode *inode;
pgoff_t pg_start;
pgoff_t pg_end;
@@ -340,6 +342,11 @@ int fuse_reverse_inval_inode(struct super_block *sb, u64 nodeid,
if (!inode)
return -ENOENT;
+ fi = get_fuse_inode(inode);
+ spin_lock(&fc->lock);
+ fi->attr_version = ++fc->attr_version;
+ spin_unlock(&fc->lock);
+
fuse_invalidate_attr(inode);
if (offset >= 0) {
pg_start = offset >> PAGE_CACHE_SHIFT;
