Re: [PATCH v3 05/11] mm, fsdax: Refactor memory-failure handler for dax mapping

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On 2021/2/8 6:55 下午, Shiyang Ruan wrote:
The current memory_failure_dev_pagemap() can only handle single-mapped
dax page for fsdax mode.  The dax page could be mapped by multiple files
and offsets if we let reflink feature & fsdax mode work together.  So,
we refactor current implementation to support handle memory failure on
each file and offset.

Signed-off-by: Shiyang Ruan <ruansy.fnst@xxxxxxxxxxxxxx>
---
  fs/dax.c            | 21 ++++++++++
  include/linux/dax.h |  1 +
  include/linux/mm.h  |  9 +++++
  mm/memory-failure.c | 98 ++++++++++++++++++++++++++++++++++-----------
  4 files changed, 105 insertions(+), 24 deletions(-)

diff --git a/fs/dax.c b/fs/dax.c
index 26d5dcd2d69e..c64c3a0e76a6 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -378,6 +378,27 @@ static struct page *dax_busy_page(void *entry)
  	return NULL;
  }
+/*
+ * dax_load_pfn - Load pfn of the DAX entry corresponding to a page
+ * @mapping: The file whose entry we want to load
+ * @index:   The offset where the DAX entry located in
+ *
+ * Return:   pfn of the DAX entry
+ */
+unsigned long dax_load_pfn(struct address_space *mapping, unsigned long index)
+{
+	XA_STATE(xas, &mapping->i_pages, index);
+	void *entry;
+	unsigned long pfn;
+
+	xas_lock_irq(&xas);
+	entry = xas_load(&xas);
+	pfn = dax_to_pfn(entry);
+	xas_unlock_irq(&xas);
+
+	return pfn;
+}
+
  /*
   * dax_lock_mapping_entry - Lock the DAX entry corresponding to a page
   * @page: The page whose entry we want to lock
diff --git a/include/linux/dax.h b/include/linux/dax.h
index b52f084aa643..89e56ceeffc7 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -150,6 +150,7 @@ int dax_writeback_mapping_range(struct address_space *mapping,
struct page *dax_layout_busy_page(struct address_space *mapping);
  struct page *dax_layout_busy_page_range(struct address_space *mapping, loff_t start, loff_t end);
+unsigned long dax_load_pfn(struct address_space *mapping, unsigned long index);
  dax_entry_t dax_lock_page(struct page *page);
  void dax_unlock_page(struct page *page, dax_entry_t cookie);
  #else
diff --git a/include/linux/mm.h b/include/linux/mm.h
index ecdf8a8cd6ae..ab52bc633d84 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1157,6 +1157,14 @@ static inline bool is_device_private_page(const struct page *page)
  		page->pgmap->type == MEMORY_DEVICE_PRIVATE;
  }
+static inline bool is_device_fsdax_page(const struct page *page)
+{
+	return IS_ENABLED(CONFIG_DEV_PAGEMAP_OPS) &&
+		IS_ENABLED(CONFIG_FS_DAX) &&
+		is_zone_device_page(page) &&
+		page->pgmap->type == MEMORY_DEVICE_FS_DAX;
+}
+
  static inline bool is_pci_p2pdma_page(const struct page *page)
  {
  	return IS_ENABLED(CONFIG_DEV_PAGEMAP_OPS) &&
@@ -3045,6 +3053,7 @@ enum mf_flags {
  	MF_MUST_KILL = 1 << 2,
  	MF_SOFT_OFFLINE = 1 << 3,
  };
+extern int mf_dax_mapping_kill_procs(struct address_space *mapping, pgoff_t index, int flags);
  extern int memory_failure(unsigned long pfn, int flags);
  extern void memory_failure_queue(unsigned long pfn, int flags);
  extern void memory_failure_queue_kick(int cpu);
diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index e9481632fcd1..158fe0c8e602 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -56,6 +56,7 @@
  #include <linux/kfifo.h>
  #include <linux/ratelimit.h>
  #include <linux/page-isolation.h>
+#include <linux/dax.h>
  #include "internal.h"
  #include "ras/ras_event.h"
@@ -120,6 +121,13 @@ static int hwpoison_filter_dev(struct page *p)
  	if (PageSlab(p))
  		return -EINVAL;
+ if (pfn_valid(page_to_pfn(p))) {
+		if (is_device_fsdax_page(p))
+			return 0;
+		else
+			return -EINVAL;
+	}
+
  	mapping = page_mapping(p);
  	if (mapping == NULL || mapping->host == NULL)
  		return -EINVAL;
@@ -286,10 +294,9 @@ void shake_page(struct page *p, int access)
  }
  EXPORT_SYMBOL_GPL(shake_page);
-static unsigned long dev_pagemap_mapping_shift(struct page *page,
-		struct vm_area_struct *vma)
+static unsigned long dev_pagemap_mapping_shift(struct vm_area_struct *vma,
+					       unsigned long address)
  {
-	unsigned long address = vma_address(page, vma);
  	pgd_t *pgd;
  	p4d_t *p4d;
  	pud_t *pud;
@@ -329,9 +336,8 @@ static unsigned long dev_pagemap_mapping_shift(struct page *page,
   * Schedule a process for later kill.
   * Uses GFP_ATOMIC allocations to avoid potential recursions in the VM.
   */
-static void add_to_kill(struct task_struct *tsk, struct page *p,
-		       struct vm_area_struct *vma,
-		       struct list_head *to_kill)
+static void add_to_kill(struct task_struct *tsk, struct page *p, pgoff_t pgoff,
+			struct vm_area_struct *vma, struct list_head *to_kill)
  {
  	struct to_kill *tk;
@@ -342,9 +348,12 @@ static void add_to_kill(struct task_struct *tsk, struct page *p,
  	}
tk->addr = page_address_in_vma(p, vma);
-	if (is_zone_device_page(p))
-		tk->size_shift = dev_pagemap_mapping_shift(p, vma);
-	else
+	if (is_zone_device_page(p)) {
+		if (is_device_fsdax_page(p))
+			tk->addr = vma->vm_start +
+					((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
+		tk->size_shift = dev_pagemap_mapping_shift(vma, tk->addr);
+	} else
  		tk->size_shift = page_shift(compound_head(p));
/*
@@ -492,7 +501,7 @@ static void collect_procs_anon(struct page *page, struct list_head *to_kill,
  			if (!page_mapped_in_vma(page, vma))
  				continue;
  			if (vma->vm_mm == t->mm)
-				add_to_kill(t, page, vma, to_kill);
+				add_to_kill(t, page, 0, vma, to_kill);
  		}
  	}
  	read_unlock(&tasklist_lock);
@@ -502,24 +511,19 @@ static void collect_procs_anon(struct page *page, struct list_head *to_kill,
  /*
   * Collect processes when the error hit a file mapped page.
   */
-static void collect_procs_file(struct page *page, struct list_head *to_kill,
-				int force_early)
+static void collect_procs_file(struct page *page, struct address_space *mapping,
+		pgoff_t pgoff, struct list_head *to_kill, int force_early)
  {
  	struct vm_area_struct *vma;
  	struct task_struct *tsk;
-	struct address_space *mapping = page->mapping;
-	pgoff_t pgoff;
i_mmap_lock_read(mapping);
  	read_lock(&tasklist_lock);
-	pgoff = page_to_pgoff(page);
  	for_each_process(tsk) {
  		struct task_struct *t = task_early_kill(tsk, force_early);
-
  		if (!t)
  			continue;
-		vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff,
-				      pgoff) {
+		vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
  			/*
  			 * Send early kill signal to tasks where a vma covers
  			 * the page but the corrupted page is not necessarily
@@ -528,7 +532,7 @@ static void collect_procs_file(struct page *page, struct list_head *to_kill,
  			 * to be informed of all such data corruptions.
  			 */
  			if (vma->vm_mm == t->mm)
-				add_to_kill(t, page, vma, to_kill);
+				add_to_kill(t, page, pgoff, vma, to_kill);
  		}
  	}
  	read_unlock(&tasklist_lock);
@@ -547,7 +551,8 @@ static void collect_procs(struct page *page, struct list_head *tokill,
  	if (PageAnon(page))
  		collect_procs_anon(page, tokill, force_early);
  	else
-		collect_procs_file(page, tokill, force_early);
+		collect_procs_file(page, page_mapping(page), page_to_pgoff(page),
+				   tokill, force_early);
  }
static const char *action_name[] = {
@@ -1214,6 +1219,50 @@ static int try_to_split_thp_page(struct page *page, const char *msg)
  	return 0;
  }
+int mf_dax_mapping_kill_procs(struct address_space *mapping, pgoff_t index, int flags)
+{
+	const bool unmap_success = true;
+	unsigned long pfn, size = 0;
+	struct to_kill *tk;
+	LIST_HEAD(to_kill);
+	int rc = -EBUSY;
+	loff_t start;
+
+	/* load the pfn of the dax mapping file */
+	pfn = dax_load_pfn(mapping, index);
+	if (!pfn)
+		return rc;
+	/*
+	 * Unlike System-RAM there is no possibility to swap in a
+	 * different physical page at a given virtual address, so all
+	 * userspace consumption of ZONE_DEVICE memory necessitates
+	 * SIGBUS (i.e. MF_MUST_KILL)
+	 */
+	flags |= MF_ACTION_REQUIRED | MF_MUST_KILL;

MF_ACTION_REQUIRED only kill the current execution context. A page can be shared
when reflink file be mapped by different process. We can not kill all process
shared the page.  Other process still can access the posioned page ?

Thanks,
zhong jiang

+	collect_procs_file(pfn_to_page(pfn), mapping, index, &to_kill,
+			   flags & MF_ACTION_REQUIRED);
+
+	list_for_each_entry(tk, &to_kill, nd)
+		if (tk->size_shift)
+			size = max(size, 1UL << tk->size_shift);
+	if (size) {
+		/*
+		 * Unmap the largest mapping to avoid breaking up
+		 * device-dax mappings which are constant size. The
+		 * actual size of the mapping being torn down is
+		 * communicated in siginfo, see kill_proc()
+		 */
+		start = (index << PAGE_SHIFT) & ~(size - 1);
+		unmap_mapping_range(mapping, start, start + size, 0);
+	}
+
+	kill_procs(&to_kill, flags & MF_MUST_KILL, !unmap_success,
+		   pfn, flags);
+	rc = 0;
+	return rc;
+}
+EXPORT_SYMBOL_GPL(mf_dax_mapping_kill_procs);
+
  static int memory_failure_hugetlb(unsigned long pfn, int flags)
  {
  	struct page *p = pfn_to_page(pfn);
@@ -1297,7 +1346,7 @@ static int memory_failure_dev_pagemap(unsigned long pfn, int flags,
  	const bool unmap_success = true;
  	unsigned long size = 0;
  	struct to_kill *tk;
-	LIST_HEAD(tokill);
+	LIST_HEAD(to_kill);
  	int rc = -EBUSY;
  	loff_t start;
  	dax_entry_t cookie;
@@ -1345,9 +1394,10 @@ static int memory_failure_dev_pagemap(unsigned long pfn, int flags,
  	 * SIGBUS (i.e. MF_MUST_KILL)
  	 */
  	flags |= MF_ACTION_REQUIRED | MF_MUST_KILL;
-	collect_procs(page, &tokill, flags & MF_ACTION_REQUIRED);
+	collect_procs_file(page, page->mapping, page->index, &to_kill,
+			   flags & MF_ACTION_REQUIRED);
- list_for_each_entry(tk, &tokill, nd)
+	list_for_each_entry(tk, &to_kill, nd)
  		if (tk->size_shift)
  			size = max(size, 1UL << tk->size_shift);
  	if (size) {
@@ -1360,7 +1410,7 @@ static int memory_failure_dev_pagemap(unsigned long pfn, int flags,
  		start = (page->index << PAGE_SHIFT) & ~(size - 1);
  		unmap_mapping_range(page->mapping, start, start + size, 0);
  	}
-	kill_procs(&tokill, flags & MF_MUST_KILL, !unmap_success, pfn, flags);
+	kill_procs(&to_kill, flags & MF_MUST_KILL, !unmap_success, pfn, flags);
  	rc = 0;
  unlock:
  	dax_unlock_page(page, cookie);

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