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From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Fri, 5 Nov 2021 13:01:27 -0700
Message-ID: <CAKwvOdkGArbV+EPJkZjEn2eOdU8JRbADp9nD7dGpKyBkCpT89A@mail.gmail.com>
Subject: Re: [PATCH] NFS: Avoid using error uninitialized in nfs_lookup()
To:     Nathan Chancellor <nathan@kernel.org>
Cc:     Trond Myklebust <trond.myklebust@hammerspace.com>,
        Anna Schumaker <anna.schumaker@netapp.com>,
        linux-nfs@vger.kernel.org, linux-kernel@vger.kernel.org,
        llvm@lists.linux.dev
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On Fri, Nov 5, 2021 at 8:57 AM Nathan Chancellor <nathan@kernel.org> wrote:
>
> Clang warns:
>
> fs/nfs/dir.c:1772:6: error: variable 'error' is used uninitialized whenever 'if' condition is true [-Werror,-Wsometimes-uninitialized]
>         if (fhandle == NULL || fattr == NULL)
>             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> fs/nfs/dir.c:1801:44: note: uninitialized use occurs here
>         trace_nfs_lookup_exit(dir, dentry, flags, error);
>                                                   ^~~~~
> fs/nfs/dir.c:1772:2: note: remove the 'if' if its condition is always false
>         if (fhandle == NULL || fattr == NULL)
>         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> fs/nfs/dir.c:1772:6: error: variable 'error' is used uninitialized whenever '||' condition is true [-Werror,-Wsometimes-uninitialized]
>         if (fhandle == NULL || fattr == NULL)
>             ^~~~~~~~~~~~~~~
> fs/nfs/dir.c:1801:44: note: uninitialized use occurs here
>         trace_nfs_lookup_exit(dir, dentry, flags, error);
>                                                   ^~~~~
> fs/nfs/dir.c:1772:6: note: remove the '||' if its condition is always false
>         if (fhandle == NULL || fattr == NULL)
>             ^~~~~~~~~~~~~~~~~~
> fs/nfs/dir.c:1754:11: note: initialize the variable 'error' to silence this warning
>         int error;
>                  ^
>                   = 0
> 2 errors generated.
>
> Add a label to skip the call to trace_nfs_lookup_exit() when the call to
> nfs_alloc_fhandle() or nfs_alloc_fattr_with_label() fails because
> trace_nfs_lookup_enter() has not been called at that point so tracing
> the exit does not make sense.
>
> Fixes: 8d3df1d0387e ("NFS: Remove the label from the nfs4_lookup_res struct")
> Link: https://github.com/ClangBuiltLinux/linux/issues/1498
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>

Thanks for the patch!
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

> ---
>  fs/nfs/dir.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
> index 8de99f426183..1c978a7cf730 100644
> --- a/fs/nfs/dir.c
> +++ b/fs/nfs/dir.c
> @@ -1770,7 +1770,7 @@ struct dentry *nfs_lookup(struct inode *dir, struct dentry * dentry, unsigned in
>         fhandle = nfs_alloc_fhandle();
>         fattr = nfs_alloc_fattr_with_label(NFS_SERVER(dir));
>         if (fhandle == NULL || fattr == NULL)
> -               goto out;
> +               goto out_no_trace;
>
>         dir_verifier = nfs_save_change_attribute(dir);
>         trace_nfs_lookup_enter(dir, dentry, flags);
> @@ -1799,6 +1799,7 @@ struct dentry *nfs_lookup(struct inode *dir, struct dentry * dentry, unsigned in
>         nfs_set_verifier(dentry, dir_verifier);
>  out:
>         trace_nfs_lookup_exit(dir, dentry, flags, error);
> +out_no_trace:
>         nfs_free_fattr(fattr);
>         nfs_free_fhandle(fhandle);
>         return res;
>
> base-commit: cb66e0e973daa668dadd43441f877377a1b7b1ff
> --
> 2.34.0.rc0
>
>


-- 
Thanks,
~Nick Desaulniers