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From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Hugh Dickins <hughd@google.com>,
	Matthew Wilcox <willy@infradead.org>,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
	Will Deacon <will@kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Linux-MM <linux-mm@kvack.org>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Jan Kara <jack@suse.cz>, Minchan Kim <minchan@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Vinayak Menon <vinmenon@codeaurora.org>,
	Android Kernel Team <kernel-team@android.com>
Subject: Re: [PATCH 1/2] mm: Allow architectures to request 'old' entries when prefaulting
Date: Sun, 27 Dec 2020 01:40:16 +0300	[thread overview]
Message-ID: <20201226224016.dxjmordcfj75xgte@box> (raw)
In-Reply-To: <CAHk-=wjesveWEQZ4tqRssSSQvuxx46LqYfME+uxKfghxAe6U_w@mail.gmail.com>

On Sat, Dec 26, 2020 at 01:16:09PM -0800, Linus Torvalds wrote:
> On Sat, Dec 26, 2020 at 1:04 PM Hugh Dickins <hughd@google.com> wrote:
> >
> >
> > Hold on. I guess this one will suffer from the same bug as the previous.
> > I was about to report back, after satisfactory overnight testing of that
> > version - provided that one big little bug is fixed:
> >
> > --- a/mm/filemap.c
> > +++ b/mm/filemap.c
> > @@ -2919,7 +2919,7 @@ static bool filemap_map_pmd(struct vm_fa
> >
> >         if (pmd_none(*vmf->pmd) &&
> >             PageTransHuge(page) &&
> > -           do_set_pmd(vmf, page)) {
> > +           do_set_pmd(vmf, page) == 0) {
> >                 unlock_page(page);
> >                 return true;
> >         }
> 
> I missed that entirely, because when just reading the patch it looks
> fine and I didn't look at what do_set_pmd() function returns outside
> the patch.
> 
> And maybe it would be better to write it as
> 
>         if (pmd_none(*vmf->pmd) && PageTransHuge(page)) {
>                 vm_fault_t ret = do_set_pmd(vmf, page);
>                 if (!ret) {
>                         ...
> 
> instead to make it a bit more explicit about how that return value is
> a vm_fault_t there...
> 
> And see my other email about how I suspect there is still a leak in
> that patch for the previous test-case.

Ughh...

Here's the fixup I have so far. It doesn't blow up immediately, but please
take a closer look. Who knows what stupid mistake I did this time. :/

diff --git a/mm/filemap.c b/mm/filemap.c
index 3a92aaa59b9b..c4b374678e7d 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2837,16 +2837,21 @@ static bool filemap_map_pmd(struct vm_fault *vmf, struct page *page)
 	struct mm_struct *mm = vmf->vma->vm_mm;
 
 	/* Huge page is mapped? No need to proceed. */
-	if (pmd_trans_huge(*vmf->pmd))
-		return true;
-
-	if (pmd_none(*vmf->pmd) &&
-	    PageTransHuge(page) &&
-	    do_set_pmd(vmf, page)) {
+	if (pmd_trans_huge(*vmf->pmd)) {
 		unlock_page(page);
+		put_page(page);
 		return true;
 	}
 
+	if (pmd_none(*vmf->pmd) && PageTransHuge(page)) {
+	    vm_fault_t ret = do_set_pmd(vmf, page);
+	    if (!ret) {
+		    /* The page is mapped successfully, reference consumed. */
+		    unlock_page(page);
+		    return true;
+	    }
+	}
+
 	if (pmd_none(*vmf->pmd)) {
 		vmf->ptl = pmd_lock(mm, vmf->pmd);
 		if (likely(pmd_none(*vmf->pmd))) {
@@ -2867,7 +2872,7 @@ static bool filemap_map_pmd(struct vm_fault *vmf, struct page *page)
 	return false;
 }
 
-static struct page *next_stable_page(struct page *page, struct vm_fault *vmf,
+static struct page *next_uptodate_page(struct page *page, struct vm_fault *vmf,
 				     struct xa_state *xas, pgoff_t end_pgoff)
 {
 	struct address_space *mapping = vmf->vma->vm_file->f_mapping;
@@ -2914,15 +2919,16 @@ static inline struct page *first_map_page(struct vm_fault *vmf,
 					  struct xa_state *xas,
 					  pgoff_t end_pgoff)
 {
-	return next_stable_page(xas_find(xas, end_pgoff), vmf, xas, end_pgoff);
+	return next_uptodate_page(xas_find(xas, end_pgoff),
+				  vmf, xas, end_pgoff);
 }
 
 static inline struct page *next_map_page(struct vm_fault *vmf,
 					  struct xa_state *xas,
 					  pgoff_t end_pgoff)
 {
-	return next_stable_page(xas_next_entry(xas, end_pgoff),
-				vmf, xas, end_pgoff);
+	return next_uptodate_page(xas_next_entry(xas, end_pgoff),
+				  vmf, xas, end_pgoff);
 }
 
 void filemap_map_pages(struct vm_fault *vmf,
-- 
 Kirill A. Shutemov

WARNING: multiple messages have this Message-ID
From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Android Kernel Team <kernel-team@android.com>,
	Jan Kara <jack@suse.cz>, Minchan Kim <minchan@kernel.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Hugh Dickins <hughd@google.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Matthew Wilcox <willy@infradead.org>,
	Linux-MM <linux-mm@kvack.org>,
	Vinayak Menon <vinmenon@codeaurora.org>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Will Deacon <will@kernel.org>,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Subject: Re: [PATCH 1/2] mm: Allow architectures to request 'old' entries when prefaulting
Date: Sun, 27 Dec 2020 01:40:16 +0300	[thread overview]
Message-ID: <20201226224016.dxjmordcfj75xgte@box> (raw)
In-Reply-To: <CAHk-=wjesveWEQZ4tqRssSSQvuxx46LqYfME+uxKfghxAe6U_w@mail.gmail.com>

On Sat, Dec 26, 2020 at 01:16:09PM -0800, Linus Torvalds wrote:
> On Sat, Dec 26, 2020 at 1:04 PM Hugh Dickins <hughd@google.com> wrote:
> >
> >
> > Hold on. I guess this one will suffer from the same bug as the previous.
> > I was about to report back, after satisfactory overnight testing of that
> > version - provided that one big little bug is fixed:
> >
> > --- a/mm/filemap.c
> > +++ b/mm/filemap.c
> > @@ -2919,7 +2919,7 @@ static bool filemap_map_pmd(struct vm_fa
> >
> >         if (pmd_none(*vmf->pmd) &&
> >             PageTransHuge(page) &&
> > -           do_set_pmd(vmf, page)) {
> > +           do_set_pmd(vmf, page) == 0) {
> >                 unlock_page(page);
> >                 return true;
> >         }
> 
> I missed that entirely, because when just reading the patch it looks
> fine and I didn't look at what do_set_pmd() function returns outside
> the patch.
> 
> And maybe it would be better to write it as
> 
>         if (pmd_none(*vmf->pmd) && PageTransHuge(page)) {
>                 vm_fault_t ret = do_set_pmd(vmf, page);
>                 if (!ret) {
>                         ...
> 
> instead to make it a bit more explicit about how that return value is
> a vm_fault_t there...
> 
> And see my other email about how I suspect there is still a leak in
> that patch for the previous test-case.

Ughh...

Here's the fixup I have so far. It doesn't blow up immediately, but please
take a closer look. Who knows what stupid mistake I did this time. :/

diff --git a/mm/filemap.c b/mm/filemap.c
index 3a92aaa59b9b..c4b374678e7d 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2837,16 +2837,21 @@ static bool filemap_map_pmd(struct vm_fault *vmf, struct page *page)
 	struct mm_struct *mm = vmf->vma->vm_mm;
 
 	/* Huge page is mapped? No need to proceed. */
-	if (pmd_trans_huge(*vmf->pmd))
-		return true;
-
-	if (pmd_none(*vmf->pmd) &&
-	    PageTransHuge(page) &&
-	    do_set_pmd(vmf, page)) {
+	if (pmd_trans_huge(*vmf->pmd)) {
 		unlock_page(page);
+		put_page(page);
 		return true;
 	}
 
+	if (pmd_none(*vmf->pmd) && PageTransHuge(page)) {
+	    vm_fault_t ret = do_set_pmd(vmf, page);
+	    if (!ret) {
+		    /* The page is mapped successfully, reference consumed. */
+		    unlock_page(page);
+		    return true;
+	    }
+	}
+
 	if (pmd_none(*vmf->pmd)) {
 		vmf->ptl = pmd_lock(mm, vmf->pmd);
 		if (likely(pmd_none(*vmf->pmd))) {
@@ -2867,7 +2872,7 @@ static bool filemap_map_pmd(struct vm_fault *vmf, struct page *page)
 	return false;
 }
 
-static struct page *next_stable_page(struct page *page, struct vm_fault *vmf,
+static struct page *next_uptodate_page(struct page *page, struct vm_fault *vmf,
 				     struct xa_state *xas, pgoff_t end_pgoff)
 {
 	struct address_space *mapping = vmf->vma->vm_file->f_mapping;
@@ -2914,15 +2919,16 @@ static inline struct page *first_map_page(struct vm_fault *vmf,
 					  struct xa_state *xas,
 					  pgoff_t end_pgoff)
 {
-	return next_stable_page(xas_find(xas, end_pgoff), vmf, xas, end_pgoff);
+	return next_uptodate_page(xas_find(xas, end_pgoff),
+				  vmf, xas, end_pgoff);
 }
 
 static inline struct page *next_map_page(struct vm_fault *vmf,
 					  struct xa_state *xas,
 					  pgoff_t end_pgoff)
 {
-	return next_stable_page(xas_next_entry(xas, end_pgoff),
-				vmf, xas, end_pgoff);
+	return next_uptodate_page(xas_next_entry(xas, end_pgoff),
+				  vmf, xas, end_pgoff);
 }
 
 void filemap_map_pages(struct vm_fault *vmf,
-- 
 Kirill A. Shutemov

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  reply	other threads:[~2020-12-26 22:41 UTC|newest]

Thread overview: 138+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-09 16:39 [PATCH 0/2] Create 'old' ptes for faultaround mappings on arm64 with hardware access flag Will Deacon
2020-12-09 16:39 ` Will Deacon
2020-12-09 16:39 ` [PATCH 1/2] mm: Allow architectures to request 'old' entries when prefaulting Will Deacon
2020-12-09 16:39   ` Will Deacon
2020-12-09 17:58   ` Linus Torvalds
2020-12-09 17:58     ` Linus Torvalds
2020-12-09 17:58     ` Linus Torvalds
2020-12-09 18:40     ` Will Deacon
2020-12-09 18:40       ` Will Deacon
2020-12-09 19:04       ` Linus Torvalds
2020-12-09 19:04         ` Linus Torvalds
2020-12-09 19:04         ` Linus Torvalds
2020-12-09 20:32         ` Matthew Wilcox
2020-12-09 20:32           ` Matthew Wilcox
2020-12-09 21:04           ` Linus Torvalds
2020-12-09 21:04             ` Linus Torvalds
2020-12-09 21:04             ` Linus Torvalds
2020-12-10 15:08         ` Kirill A. Shutemov
2020-12-10 15:08           ` Kirill A. Shutemov
2020-12-10 17:23           ` Linus Torvalds
2020-12-10 17:23             ` Linus Torvalds
2020-12-10 17:23             ` Linus Torvalds
2020-12-14 16:07             ` Kirill A. Shutemov
2020-12-14 16:07               ` Kirill A. Shutemov
2020-12-14 17:54               ` Linus Torvalds
2020-12-14 17:54                 ` Linus Torvalds
2020-12-14 17:54                 ` Linus Torvalds
2020-12-14 18:56                 ` Matthew Wilcox
2020-12-14 18:56                   ` Matthew Wilcox
2020-12-16 17:07                 ` Kirill A. Shutemov
2020-12-16 17:07                   ` Kirill A. Shutemov
2020-12-16 18:41                   ` Linus Torvalds
2020-12-16 18:41                     ` Linus Torvalds
2020-12-16 18:41                     ` Linus Torvalds
2020-12-17 10:54                     ` Kirill A. Shutemov
2020-12-17 10:54                       ` Kirill A. Shutemov
2020-12-17 18:22                       ` Linus Torvalds
2020-12-17 18:22                         ` Linus Torvalds
2020-12-17 18:22                         ` Linus Torvalds
2020-12-18 11:04                         ` Kirill A. Shutemov
2020-12-18 11:04                           ` Kirill A. Shutemov
2020-12-18 18:56                           ` Linus Torvalds
2020-12-18 18:56                             ` Linus Torvalds
2020-12-18 18:56                             ` Linus Torvalds
2020-12-19 12:41                             ` Kirill A. Shutemov
2020-12-19 12:41                               ` Kirill A. Shutemov
2020-12-19 20:08                               ` Linus Torvalds
2020-12-19 20:08                                 ` Linus Torvalds
2020-12-19 20:08                                 ` Linus Torvalds
2020-12-19 20:34                               ` Linus Torvalds
2020-12-19 20:34                                 ` Linus Torvalds
2020-12-19 20:34                                 ` Linus Torvalds
2020-12-22 10:00                                 ` Kirill A. Shutemov
2020-12-22 10:00                                   ` Kirill A. Shutemov
2020-12-24  4:04                                   ` Hugh Dickins
2020-12-24  4:04                                     ` Hugh Dickins
2020-12-24  4:04                                     ` Hugh Dickins
2020-12-25 11:31                                     ` Kirill A. Shutemov
2020-12-25 11:31                                       ` Kirill A. Shutemov
2020-12-26 17:57                                       ` Linus Torvalds
2020-12-26 17:57                                         ` Linus Torvalds
2020-12-26 17:57                                         ` Linus Torvalds
2020-12-26 20:43                                         ` Kirill A. Shutemov
2020-12-26 20:43                                           ` Kirill A. Shutemov
2020-12-26 21:03                                           ` Hugh Dickins
2020-12-26 21:03                                             ` Hugh Dickins
2020-12-26 21:03                                             ` Hugh Dickins
2020-12-26 21:16                                             ` Linus Torvalds
2020-12-26 21:16                                               ` Linus Torvalds
2020-12-26 21:16                                               ` Linus Torvalds
2020-12-26 22:40                                               ` Kirill A. Shutemov [this message]
2020-12-26 22:40                                                 ` Kirill A. Shutemov
2020-12-27  0:45                                                 ` Hugh Dickins
2020-12-27  0:45                                                   ` Hugh Dickins
2020-12-27  0:45                                                   ` Hugh Dickins
2020-12-27  2:38                                                   ` Hugh Dickins
2020-12-27  2:38                                                     ` Hugh Dickins
2020-12-27  2:38                                                     ` Hugh Dickins
2020-12-27 19:38                                                     ` Linus Torvalds
2020-12-27 19:38                                                       ` Linus Torvalds
2020-12-27 19:38                                                       ` Linus Torvalds
2020-12-27 20:32                                                       ` Damian Tometzki
2020-12-27 20:32                                                         ` Damian Tometzki
2020-12-27 22:35                                                         ` Hugh Dickins
2020-12-27 22:35                                                           ` Hugh Dickins
2020-12-27 22:35                                                           ` Hugh Dickins
2020-12-27 23:12                                                           ` Linus Torvalds
2020-12-27 23:12                                                             ` Linus Torvalds
2020-12-27 23:12                                                             ` Linus Torvalds
2020-12-27 23:40                                                             ` Linus Torvalds
2020-12-27 23:40                                                               ` Linus Torvalds
2020-12-27 23:40                                                               ` Linus Torvalds
2020-12-27 23:55                                                               ` Kirill A. Shutemov
2020-12-27 23:55                                                                 ` Kirill A. Shutemov
2020-12-27 23:48                                                       ` Kirill A. Shutemov
2020-12-27 23:48                                                         ` Kirill A. Shutemov
2020-12-28  1:54                                                         ` Linus Torvalds
2020-12-28  1:54                                                           ` Linus Torvalds
2020-12-28  1:54                                                           ` Linus Torvalds
2020-12-28  6:43                                                           ` Hugh Dickins
2020-12-28  6:43                                                             ` Hugh Dickins
2020-12-28  6:43                                                             ` Hugh Dickins
2020-12-28 12:53                                                             ` Kirill A. Shutemov
2020-12-28 12:53                                                               ` Kirill A. Shutemov
2020-12-28 18:47                                                               ` Linus Torvalds
2020-12-28 18:47                                                                 ` Linus Torvalds
2020-12-28 18:47                                                                 ` Linus Torvalds
2020-12-28 21:58                                                                 ` Linus Torvalds
2020-12-28 21:58                                                                   ` Linus Torvalds
2020-12-28 21:58                                                                   ` Linus Torvalds
2020-12-29 13:28                                                                   ` Kirill A. Shutemov
2020-12-29 13:28                                                                     ` Kirill A. Shutemov
2020-12-29 15:19                                                                     ` Matthew Wilcox
2020-12-29 15:19                                                                       ` Matthew Wilcox
2020-12-29 20:52                                                                     ` Linus Torvalds
2020-12-29 20:52                                                                       ` Linus Torvalds
2020-12-29 20:52                                                                       ` Linus Torvalds
2020-12-28 22:05                                                                 ` Kirill A. Shutemov
2020-12-28 22:05                                                                   ` Kirill A. Shutemov
2020-12-28 22:12                                                                   ` Kirill A. Shutemov
2020-12-28 22:12                                                                     ` Kirill A. Shutemov
2020-12-29  4:35                                                                     ` Hugh Dickins
2020-12-29  4:35                                                                       ` Hugh Dickins
2020-12-29  4:35                                                                       ` Hugh Dickins
2020-12-28 23:28                                                                   ` Linus Torvalds
2020-12-28 23:28                                                                     ` Linus Torvalds
2020-12-28 23:28                                                                     ` Linus Torvalds
2020-12-26 21:07                                           ` Linus Torvalds
2020-12-26 21:07                                             ` Linus Torvalds
2020-12-26 21:07                                             ` Linus Torvalds
2020-12-26 21:41                                           ` Matthew Wilcox
2020-12-26 21:41                                             ` Matthew Wilcox
2020-12-09 16:39 ` [PATCH 2/2] arm64: mm: Implement arch_wants_old_faultaround_pte() Will Deacon
2020-12-09 16:39   ` Will Deacon
2020-12-09 18:35   ` Catalin Marinas
2020-12-09 18:35     ` Catalin Marinas
2020-12-09 18:46     ` Will Deacon
2020-12-09 18:46       ` Will Deacon

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