linux-kernel - Re: [PATCH v3] mm: Change return type int to vm_fault

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Date:   Tue, 24 Jul 2018 15:36:21 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Souptick Joarder <jrdr.linux@...il.com>
Cc:     willy@...radead.org, viro@...iv.linux.org.uk, hughd@...gle.com,
        mhocko@...e.com, ross.zwisler@...ux.intel.com,
        zi.yan@...rutgers.edu, kirill.shutemov@...ux.intel.com,
        dan.j.williams@...el.com, gregkh@...uxfoundation.org,
        mark.rutland@....com, riel@...hat.com, pasha.tatashin@...cle.com,
        jschoenh@...zon.de, kstewart@...uxfoundation.org,
        rientjes@...gle.com, tglx@...utronix.de, peterz@...radead.org,
        mgorman@...e.de, yang.s@...baba-inc.com, minchan@...nel.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH v3] mm: Change return type int to vm_fault_t for fault
 handlers

On Mon, 4 Jun 2018 22:47:27 +0530 Souptick Joarder <jrdr.linux@...il.com> wrote:

> Use new return type vm_fault_t for fault handler. For
> now, this is just documenting that the function returns
> a VM_FAULT value rather than an errno. Once all instances
> are converted, vm_fault_t will become a distinct type.
> 
> Ref-> commit 1c8f422059ae ("mm: change return type to vm_fault_t")
> 
> The aim is to change the return type of finish_fault()
> and handle_mm_fault() to vm_fault_t type. As part of
> that clean up return type of all other recursively called
> functions have been changed to vm_fault_t type.
> 
> The places from where handle_mm_fault() is getting invoked
> will be change to vm_fault_t type but in a separate patch.
> 
> vmf_error() is the newly introduce inline function
> in 4.17-rc6.

Looks OK.

For some reason the shmem.c changes are already present.

One incidental fixup:

From: Andrew Morton <akpm@...ux-foundation.org>
Subject: mm-change-return-type-int-to-vm_fault_t-for-fault-handlers-fix

don't shadow outer local `ret' in __do_huge_pmd_anonymous_page()

--- a/mm/huge_memory.c~mm-change-return-type-int-to-vm_fault_t-for-fault-handlers-fix
+++ a/mm/huge_memory.c
@@ -584,15 +584,15 @@ static vm_fault_t __do_huge_pmd_anonymou
 
 		/* Deliver the page fault to userland */
 		if (userfaultfd_missing(vma)) {
-			vm_fault_t ret;
+			vm_fault_t ret2;
 
 			spin_unlock(vmf->ptl);
 			mem_cgroup_cancel_charge(page, memcg, true);
 			put_page(page);
 			pte_free(vma->vm_mm, pgtable);
-			ret = handle_userfault(vmf, VM_UFFD_MISSING);
-			VM_BUG_ON(ret & VM_FAULT_FALLBACK);
-			return ret;
+			ret2 = handle_userfault(vmf, VM_UFFD_MISSING);
+			VM_BUG_ON(ret2 & VM_FAULT_FALLBACK);
+			return ret2;
 		}
 
 		entry = mk_huge_pmd(page, vma->vm_page_prot);