[POWERPC] spufs: Fix lost events in poll/epoll on mfc

When waiting for I/O events on mfc in an SPU context by using
poll/epoll syscalls, some of the events can be lost because of wrong
order of poll_wait and MFC status checks in the spufs_mfc_poll
function and non-atomic update of tagwait.  This fixes the
problem.

Signed-off-by: Kazunori Asayama <asayama@sm.sony.co.jp>
Signed-off-by: Jeremy Kerr <jk@ozlabs.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>

1 files changed, 5 insertions, 4 deletions

diff --git a/arch/powerpc/platforms/cell/spufs/file.c b/arch/powerpc/platforms/cell/spufs/file.c
index 30f7b077f347..c2814ea96af2 100644
--- a/arch/powerpc/platforms/cell/spufs/file.c
+++ b/arch/powerpc/platforms/cell/spufs/file.c
@@ -1499,14 +1499,15 @@ static ssize_t spufs_mfc_write(struct file *file, const char __user *buffer,
                 if (status)
                         ret = status;
         }
-        spu_release(ctx);
 
         if (ret)
-                goto out;
+                goto out_unlock;
 
         ctx->tagwait |= 1 << cmd.tag;
         ret = size;
 
+out_unlock:
+        spu_release(ctx);
 out:
         return ret;
 }
@@ -1517,14 +1518,14 @@ static unsigned int spufs_mfc_poll(struct file *file,poll_table *wait)
         u32 free_elements, tagstatus;
         unsigned int mask;
 
+        poll_wait(file, &ctx->mfc_wq, wait);
+
         spu_acquire(ctx);
         ctx->ops->set_mfc_query(ctx, ctx->tagwait, 2);
         free_elements = ctx->ops->get_mfc_free_elements(ctx);
         tagstatus = ctx->ops->read_mfc_tagstatus(ctx);
         spu_release(ctx);
 
-        poll_wait(file, &ctx->mfc_wq, wait);
-
         mask = 0;
         if (free_elements & 0xffff)
                 mask |= POLLOUT | POLLWRNORM;