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authorMiklos Szeredi <miklos@szeredi.hu>2006-01-16 22:14:52 -0800
committerLinus Torvalds <torvalds@g5.osdl.org>2006-01-16 23:15:31 -0800
commit095da6cbb6a1c54c19b11190218eb0fbac666b6d (patch)
tree29ba46cea17454fe1888182f6722aee64e1a7ef5 /fs/fuse
parentbacac382fbf53f717ca7f83558e45cce44e67df9 (diff)
downloadlinux-095da6cbb6a1c54c19b11190218eb0fbac666b6d.tar.bz2
[PATCH] fuse: fix bitfield race
Fix race in setting bitfields of fuse_conn. Spotted by Andrew Morton. The two fields ->connected and ->mounted were always changed with the fuse_lock held. But other bitfields in the same structure were changed without the lock. In theory this could lead to losing the assignment of even the ones under lock. The chosen solution is to change these two fields to be a full unsigned type. The other bitfields aren't "important" enough to warrant the extra complexity of full locking or changing them to bitops. For all bitfields document why they are safe wrt. concurrent assignments. Also make the initialization of the 'num_waiting' atomic counter explicit. Signed-off-by: Miklos Szeredi <miklos@szeredi.hu> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'fs/fuse')
-rw-r--r--fs/fuse/fuse_i.h24
-rw-r--r--fs/fuse/inode.c2
2 files changed, 23 insertions, 3 deletions
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index 7ed1d3c53b8a..46cf933aa3bf 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -94,6 +94,11 @@ struct fuse_out {
/** Header returned from userspace */
struct fuse_out_header h;
+ /*
+ * The following bitfields are not changed during the request
+ * processing
+ */
+
/** Last argument is variable length (can be shorter than
arg->size) */
unsigned argvar:1;
@@ -136,6 +141,12 @@ struct fuse_req {
/** refcount */
atomic_t count;
+ /*
+ * The following bitfields are either set once before the
+ * request is queued or setting/clearing them is protected by
+ * fuse_lock
+ */
+
/** True if the request has reply */
unsigned isreply:1;
@@ -250,15 +261,22 @@ struct fuse_conn {
u64 reqctr;
/** Mount is active */
- unsigned mounted : 1;
+ unsigned mounted;
/** Connection established, cleared on umount, connection
abort and device release */
- unsigned connected : 1;
+ unsigned connected;
- /** Connection failed (version mismatch) */
+ /** Connection failed (version mismatch). Cannot race with
+ setting other bitfields since it is only set once in INIT
+ reply, before any other request, and never cleared */
unsigned conn_error : 1;
+ /*
+ * The following bitfields are only for optimization purposes
+ * and hence races in setting them will not cause malfunction
+ */
+
/** Is fsync not implemented by fs? */
unsigned no_fsync : 1;
diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index 8683e7254d53..c755a0440a66 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -397,6 +397,7 @@ static struct fuse_conn *new_conn(void)
init_rwsem(&fc->sbput_sem);
kobj_set_kset_s(fc, connections_subsys);
kobject_init(&fc->kobj);
+ atomic_set(&fc->num_waiting, 0);
for (i = 0; i < FUSE_MAX_OUTSTANDING; i++) {
struct fuse_req *req = fuse_request_alloc();
if (!req) {
@@ -492,6 +493,7 @@ static void fuse_send_init(struct fuse_conn *fc)
to be exactly one request available */
struct fuse_req *req = fuse_get_request(fc);
struct fuse_init_in *arg = &req->misc.init_in;
+
arg->major = FUSE_KERNEL_VERSION;
arg->minor = FUSE_KERNEL_MINOR_VERSION;
req->in.h.opcode = FUSE_INIT;