On Mon, Feb 02, 2026 at 02:51:33PM +0800, Jianping wrote:
>
>
> On 1/16/2026 4:47 AM, Dmitry Baryshkov wrote:
> > On Thu, Jan 15, 2026 at 04:28:50PM +0800, Jianping Li wrote:
> > > From: Ekansh Gupta <[email protected]>
> > >
> > > fastrpc_req_munmap_impl() is called to unmap any buffer. The buffer is
> > > getting removed from the list after it is unmapped from DSP. This can
> > > create potential race conditions if any other thread removes the entry
> > > from list while unmap operation is ongoing. Remove the entry before
> > > calling unmap operation.
> > >
> > > Fixes: 2419e55e532de ("misc: fastrpc: add mmap/unmap support")
> > > Cc: [email protected]
> > > Co-developed-by: Ekansh Gupta <[email protected]>
> > > Signed-off-by: Ekansh Gupta <[email protected]>
> > > Signed-off-by: Jianping Li <[email protected]>
> > > ---
> > > drivers/misc/fastrpc.c | 28 ++++++++++++++++++++--------
> > > 1 file changed, 20 insertions(+), 8 deletions(-)
> > >
> > > diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
> > > index 4f12fa5a05aa..833c265add5e 100644
> > > --- a/drivers/misc/fastrpc.c
> > > +++ b/drivers/misc/fastrpc.c
> > > @@ -202,6 +202,8 @@ struct fastrpc_buf {
> > > /* mmap support */
> > > struct list_head node; /* list of user requested mmaps */
> > > uintptr_t raddr;
> > > + /* Lock for buf->node */
> > > + spinlock_t *list_lock;
> >
> > Why do you need to lock this? Isn't fl->lock enough?
>
> According to the discussion in v1 patch:
> https://lore.kernel.org/all/p6cc5lxufmefeulx5bhlh6q6ivwluqf2muj3hu5e5526fsppuu@brcy6arm7epg/
>
> The lock is stored in fastrpc_buf here.
That was a separate topic. So, why fl->lock isn't enough? What is the
race that isn't prevented by it?
> >
> > > };
> > > struct fastrpc_dma_buf_attachment {
> > > @@ -441,6 +443,7 @@ static int __fastrpc_buf_alloc(struct fastrpc_user
> > > *fl, struct device *dev,
> > > buf->size = size;
> > > buf->dev = dev;
> > > buf->raddr = 0;
> > > + buf->list_lock = &fl->lock;
> > > buf->virt = dma_alloc_coherent(dev, buf->size, &buf->dma_addr,
> > > GFP_KERNEL);
> > > @@ -1865,9 +1868,6 @@ static int fastrpc_req_munmap_impl(struct
> > > fastrpc_user *fl, struct fastrpc_buf *
> > > &args[0]);
> > > if (!err) {
> > > dev_dbg(dev, "unmmap\tpt 0x%09lx OK\n", buf->raddr);
> > > - spin_lock(&fl->lock);
> > > - list_del(&buf->node);
> > > - spin_unlock(&fl->lock);
> > > fastrpc_buf_free(buf);
> > > } else {
> > > dev_err(dev, "unmmap\tpt 0x%09lx ERROR\n", buf->raddr);
> > > @@ -1881,6 +1881,7 @@ static int fastrpc_req_munmap(struct fastrpc_user
> > > *fl, char __user *argp)
> > > struct fastrpc_buf *buf = NULL, *iter, *b;
> > > struct fastrpc_req_munmap req;
> > > struct device *dev = fl->sctx->dev;
> > > + int err;
> > > if (copy_from_user(&req, argp, sizeof(req)))
> > > return -EFAULT;
> > > @@ -1888,6 +1889,7 @@ static int fastrpc_req_munmap(struct fastrpc_user
> > > *fl, char __user *argp)
> > > spin_lock(&fl->lock);
> > > list_for_each_entry_safe(iter, b, &fl->mmaps, node) {
> > > if ((iter->raddr == req.vaddrout) && (iter->size ==
> > > req.size)) {
> > > + list_del(&iter->node);
> > > buf = iter;
> > > break;
> > > }
> > > @@ -1900,7 +1902,14 @@ static int fastrpc_req_munmap(struct fastrpc_user
> > > *fl, char __user *argp)
> > > return -EINVAL;
> > > }
> > > - return fastrpc_req_munmap_impl(fl, buf);
> > > + err = fastrpc_req_munmap_impl(fl, buf);
> > > + if (err) {
> > > + spin_lock(buf->list_lock);
> > > + list_add_tail(&buf->node, &fl->mmaps);
> > > + spin_unlock(buf->list_lock);
> > > + }
> > > +
> > > + return err;
> > > }
> > > static int fastrpc_req_mmap(struct fastrpc_user *fl, char __user *argp)
> > > @@ -1985,20 +1994,23 @@ static int fastrpc_req_mmap(struct fastrpc_user
> > > *fl, char __user *argp)
> > > }
> > > }
> > > - spin_lock(&fl->lock);
> > > + spin_lock(buf->list_lock);
> > > list_add_tail(&buf->node, &fl->mmaps);
> > > - spin_unlock(&fl->lock);
> > > + spin_unlock(buf->list_lock);
> > > if (copy_to_user((void __user *)argp, &req, sizeof(req))) {
> > > err = -EFAULT;
> > > - goto err_assign;
> > > + goto err_copy;
> > > }
> > > dev_dbg(dev, "mmap\t\tpt 0x%09lx OK [len 0x%08llx]\n",
> > > buf->raddr, buf->size);
> > > return 0;
> > > -
> > > +err_copy:
> > > + spin_lock(buf->list_lock);
> > > + list_del(&buf->node);
> > > + spin_unlock(buf->list_lock);
> > > err_assign:
> > > fastrpc_req_munmap_impl(fl, buf);
> > > --
> > > 2.43.0
> > >
> >
>
--
With best wishes
Dmitry
