Re: [PATCH v1 1/2] iommufd/fault: Fix out_fput in iommufd_fault_alloc()

[Yi Liu]

On 2024/12/3 16:02, Nicolin Chen wrote:

As fput() calls the file->f_op->release op, where fault obj and ictx are
getting released, there is no need to release these two after fput() one
more time, which would result in imbalanced refcounts:
   refcount_t: decrement hit 0; leaking memory.
   WARNING: CPU: 48 PID: 2369 at lib/refcount.c:31 
refcount_warn_saturate+0x60/0x230
   Call trace:
    refcount_warn_saturate+0x60/0x230 (P)
    refcount_warn_saturate+0x60/0x230 (L)
    iommufd_fault_fops_release+0x9c/0xe0 [iommufd]
   ...
   VFS: Close: file count is 0 (f_op=iommufd_fops [iommufd])
   WARNING: CPU: 48 PID: 2369 at fs/open.c:1507 filp_flush+0x3c/0xf0
   Call trace:
    filp_flush+0x3c/0xf0 (P)
    filp_flush+0x3c/0xf0 (L)
    __arm64_sys_close+0x34/0x98
   ...
   imbalanced put on file reference count
   WARNING: CPU: 48 PID: 2369 at fs/file.c:74 __file_ref_put+0x100/0x138
   Call trace:
    __file_ref_put+0x100/0x138 (P)
    __file_ref_put+0x100/0x138 (L)
    __fput_sync+0x4c/0xd0

Drop those two lines to fix the warnings above.

Fixes: 07838f7fd529 ("iommufd: Add iommufd fault object")
Cc: sta...@vger.kernel.org
Signed-off-by: Nicolin Chen <nicol...@nvidia.com>
---
  drivers/iommu/iommufd/fault.c | 2 --
  1 file changed, 2 deletions(-)

diff --git a/drivers/iommu/iommufd/fault.c b/drivers/iommu/iommufd/fault.c
index 053b0e30f55a..1fe804e28a86 100644
--- a/drivers/iommu/iommufd/fault.c
+++ b/drivers/iommu/iommufd/fault.c
@@ -420,8 +420,6 @@ int iommufd_fault_alloc(struct iommufd_ucmd *ucmd)
        put_unused_fd(fdno);
  out_fput:
        fput(filep);
-       refcount_dec(&fault->obj.users);
-       iommufd_ctx_put(fault->ictx);
  out_abort:
        iommufd_object_abort_and_destroy(ucmd->ictx, &fault->obj);

Reviewed-by: Yi Liu <yi.l....@intel.com>

--
Regards,
Yi Liu