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Lockdep issues a circular dependency warning when AFS issues an operation
through AF_RXRPC from a context in which the VFS/VM holds the mmap_sem.
The theory lockdep comes up with is as follows:
(1) If the pagefault handler decides it needs to read pages from AFS, it
calls AFS with mmap_sem held and AFS begins an AF_RXRPC call, but
creating a call requires the socket lock:
mmap_sem must be taken before sk_lock-AF_RXRPC
(2) afs_open_socket() opens an AF_RXRPC socket and binds it. rxrpc_bind()
binds the underlying UDP socket whilst holding its socket lock.
inet_bind() takes its own socket lock:
sk_lock-AF_RXRPC must be taken before sk_lock-AF_INET
(3) Reading from a TCP socket into a userspace buffer might cause a fault
and thus cause the kernel to take the mmap_sem, but the TCP socket is
locked whilst doing this:
sk_lock-AF_INET must be taken before mmap_sem
However, lockdep's theory is wrong in this instance because it deals only
with lock classes and not individual locks. The AF_INET lock in (2) isn't
really equivalent to the AF_INET lock in (3) as the former deals with a
socket entirely internal to the kernel that never sees userspace. This is
a limitation in the design of lockdep.
Fix the general case by:
(1) Double up all the locking keys used in sockets so that one set are
used if the socket is created by userspace and the other set is used
if the socket is created by the kernel.
(2) Store the kern parameter passed to sk_alloc() in a variable in the
sock struct (sk_kern_sock). This informs sock_lock_init(),
sock_init_data() and sk_clone_lock() as to the lock keys to be used.
Note that the child created by sk_clone_lock() inherits the parent's
kern setting.
(3) Add a 'kern' parameter to ->accept() that is analogous to the one
passed in to ->create() that distinguishes whether kernel_accept() or
sys_accept4() was the caller and can be passed to sk_alloc().
Note that a lot of accept functions merely dequeue an already
allocated socket. I haven't touched these as the new socket already
exists before we get the parameter.
Note also that there are a couple of places where I've made the accepted
socket unconditionally kernel-based:
irda_accept()
rds_rcp_accept_one()
tcp_accept_from_sock()
because they follow a sock_create_kern() and accept off of that.
Whilst creating this, I noticed that lustre and ocfs don't create sockets
through sock_create_kern() and thus they aren't marked as for-kernel,
though they appear to be internal. I wonder if these should do that so
that they use the new set of lock keys.
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
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| .. | ||
| include/linux | ||
| lnet | ||
| lustre | ||
| Kconfig | ||
| Makefile | ||
| README.txt | ||
| sysfs-fs-lustre | ||
| TODO | ||
Lustre Parallel Filesystem Client ================================= The Lustre file system is an open-source, parallel file system that supports many requirements of leadership class HPC simulation environments. Born from from a research project at Carnegie Mellon University, the Lustre file system is a widely-used option in HPC. The Lustre file system provides a POSIX compliant file system interface, can scale to thousands of clients, petabytes of storage and hundreds of gigabytes per second of I/O bandwidth. Unlike shared disk storage cluster filesystems (e.g. OCFS2, GFS, GPFS), Lustre has independent Metadata and Data servers that clients can access in parallel to maximize performance. In order to use Lustre client you will need to download the "lustre-client" package that contains the userspace tools from http://lustre.org/download/ You will need to install and configure your Lustre servers separately. Mount Syntax ============ After you installed the lustre-client tools including mount.lustre binary you can mount your Lustre filesystem with: mount -t lustre mgs:/fsname mnt where mgs is the host name or ip address of your Lustre MGS(management service) fsname is the name of the filesystem you would like to mount. Mount Options ============= noflock Disable posix file locking (Applications trying to use the functionality will get ENOSYS) localflock Enable local flock support, using only client-local flock (faster, for applications that require flock but do not run on multiple nodes). flock Enable cluster-global posix file locking coherent across all client nodes. user_xattr, nouser_xattr Support "user." extended attributes (or not) user_fid2path, nouser_fid2path Enable FID to path translation by regular users (or not) checksum, nochecksum Verify data consistency on the wire and in memory as it passes between the layers (or not). lruresize, nolruresize Allow lock LRU to be controlled by memory pressure on the server (or only 100 (default, controlled by lru_size proc parameter) locks per CPU per server on this client). lazystatfs, nolazystatfs Do not block in statfs() if some of the servers are down. 32bitapi Shrink inode numbers to fit into 32 bits. This is necessary if you plan to reexport Lustre filesystem from this client via NFSv4. verbose, noverbose Enable mount/umount console messages (or not) More Information ================ You can get more information at the Lustre website: http://wiki.lustre.org/ Source for the userspace tools and out-of-tree client and server code is available at: http://git.hpdd.intel.com/fs/lustre-release.git Latest binary packages: http://lustre.org/download/