fuse: allow interrupt queuing without fc->lock
Interrupt is only queued after the request has been sent to userspace.
This is either done in request_wait_answer() or fuse_dev_do_read()
depending on which state the request is in at the time of the interrupt.
If it's not yet sent, then queuing the interrupt is postponed until the
request is read. Otherwise (the request has already been read and is
waiting for an answer) the interrupt is queued immedidately.
We want to call queue_interrupt() without fc->lock protection, in which
case there can be a race between the two functions:
- neither of them queue the interrupt (thinking the other one has already
done it).
- both of them queue the interrupt
The first one is prevented by adding memory barriers, the second is
prevented by checking (under fiq->waitq.lock) if the interrupt has already
been queued.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index 65ad9b1..c7f1a63 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -423,8 +423,10 @@
static void queue_interrupt(struct fuse_iqueue *fiq, struct fuse_req *req)
{
spin_lock(&fiq->waitq.lock);
- list_add_tail(&req->intr_entry, &fiq->interrupts);
- wake_up_locked(&fiq->waitq);
+ if (list_empty(&req->intr_entry)) {
+ list_add_tail(&req->intr_entry, &fiq->interrupts);
+ wake_up_locked(&fiq->waitq);
+ }
spin_unlock(&fiq->waitq.lock);
kill_fasync(&fiq->fasync, SIGIO, POLL_IN);
}
@@ -443,6 +445,8 @@
spin_lock(&fc->lock);
set_bit(FR_INTERRUPTED, &req->flags);
+ /* matches barrier in fuse_dev_do_read() */
+ smp_mb__after_atomic();
if (test_bit(FR_SENT, &req->flags))
queue_interrupt(fiq, req);
spin_unlock(&fc->lock);
@@ -1358,8 +1362,10 @@
if (!test_bit(FR_ISREPLY, &req->flags)) {
request_end(fc, req);
} else {
- set_bit(FR_SENT, &req->flags);
list_move_tail(&req->list, &fc->processing);
+ set_bit(FR_SENT, &req->flags);
+ /* matches barrier in request_wait_answer() */
+ smp_mb__after_atomic();
if (test_bit(FR_INTERRUPTED, &req->flags))
queue_interrupt(fiq, req);
spin_unlock(&fc->lock);