1 files changed, 32 insertions, 41 deletions

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 757f6b0accfe..2044fe8920c2 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -7,21 +7,26 @@
  * Free Software Foundation.
  *
  * High level machine check handler. Handles pages reported by the
- * hardware as being corrupted usually due to a 2bit ECC memory or cache
+ * hardware as being corrupted usually due to a multi-bit ECC memory or cache
  * failure.
+ * 
+ * In addition there is a "soft offline" entry point that allows stop using
+ * not-yet-corrupted-by-suspicious pages without killing anything.
  *
  * Handles page cache pages in various states.  The tricky part
- * here is that we can access any page asynchronous to other VM
- * users, because memory failures could happen anytime and anywhere,
- * possibly violating some of their assumptions. This is why this code
- * has to be extremely careful. Generally it tries to use normal locking
- * rules, as in get the standard locks, even if that means the
- * error handling takes potentially a long time.
- *
- * The operation to map back from RMAP chains to processes has to walk
- * the complete process list and has non linear complexity with the number
- * mappings. In short it can be quite slow. But since memory corruptions
- * are rare we hope to get away with this.
+ * here is that we can access any page asynchronously in respect to 
+ * other VM users, because memory failures could happen anytime and 
+ * anywhere. This could violate some of their assumptions. This is why 
+ * this code has to be extremely careful. Generally it tries to use 
+ * normal locking rules, as in get the standard locks, even if that means 
+ * the error handling takes potentially a long time.
+ * 
+ * There are several operations here with exponential complexity because
+ * of unsuitable VM data structures. For example the operation to map back 
+ * from RMAP chains to processes has to walk the complete process list and 
+ * has non linear complexity with the number. But since memory corruptions
+ * are rare we hope to get away with this. This avoids impacting the core 
+ * VM.
  */
 
 /*
@@ -30,7 +35,6 @@
  * - kcore/oldmem/vmcore/mem/kmem check for hwpoison pages
  * - pass bad pages to kdump next kernel
  */
-#define DEBUG 1         /* remove me in 2.6.34 */
 #include <linux/kernel.h>
 #include <linux/mm.h>
 #include <linux/page-flags.h>
@@ -78,7 +82,7 @@ static int hwpoison_filter_dev(struct page *p)
                 return 0;
 
         /*
-         * page_mapping() does not accept slab page
+         * page_mapping() does not accept slab pages.
          */
         if (PageSlab(p))
                 return -EINVAL;
@@ -268,7 +272,7 @@ struct to_kill {
         struct list_head nd;
         struct task_struct *tsk;
         unsigned long addr;
-        unsigned addr_valid:1;
+        char addr_valid;
 };
 
 /*
@@ -309,7 +313,7 @@ static void add_to_kill(struct task_struct *tsk, struct page *p,
          * a SIGKILL because the error is not contained anymore.
          */
         if (tk->addr == -EFAULT) {
-                pr_debug("MCE: Unable to find user space address %lx in %s\n",
+                pr_info("MCE: Unable to find user space address %lx in %s\n",
                         page_to_pfn(p), tsk->comm);
                 tk->addr_valid = 0;
         }
@@ -577,7 +581,7 @@ static int me_pagecache_clean(struct page *p, unsigned long pfn)
                                         pfn, err);
                 } else if (page_has_private(p) &&
                                 !try_to_release_page(p, GFP_NOIO)) {
-                        pr_debug("MCE %#lx: failed to release buffers\n", pfn);
+                        pr_info("MCE %#lx: failed to release buffers\n", pfn);
                 } else {
                         ret = RECOVERED;
                 }
@@ -836,8 +840,6 @@ static int page_action(struct page_state *ps, struct page *p,
         return (result == RECOVERED || result == DELAYED) ? 0 : -EBUSY;
 }
 
-#define N_UNMAP_TRIES 5
-
 /*
  * Do all that is necessary to remove user space mappings. Unmap
  * the pages and send SIGBUS to the processes if the data was dirty.
@@ -849,7 +851,6 @@ static int hwpoison_user_mappings(struct page *p, unsigned long pfn,
         struct address_space *mapping;
         LIST_HEAD(tokill);
         int ret;
-        int i;
         int kill = 1;
         struct page *hpage = compound_head(p);
 
@@ -903,17 +904,7 @@ static int hwpoison_user_mappings(struct page *p, unsigned long pfn,
         if (kill)
                 collect_procs(hpage, &tokill);
 
-        /*
-         * try_to_unmap can fail temporarily due to races.
-         * Try a few times (RED-PEN better strategy?)
-         */
-        for (i = 0; i < N_UNMAP_TRIES; i++) {
-                ret = try_to_unmap(hpage, ttu);
-                if (ret == SWAP_SUCCESS)
-                        break;
-                pr_debug("MCE %#lx: try_to_unmap retry needed %d\n", pfn,  ret);
-        }
-
+        ret = try_to_unmap(hpage, ttu);
         if (ret != SWAP_SUCCESS)
                 printk(KERN_ERR "MCE %#lx: failed to unmap page (mapcount=%d)\n",
                                 pfn, page_mapcount(hpage));
@@ -1147,7 +1138,7 @@ int unpoison_memory(unsigned long pfn)
         page = compound_head(p);
 
         if (!PageHWPoison(p)) {
-                pr_debug("MCE: Page was already unpoisoned %#lx\n", pfn);
+                pr_info("MCE: Page was already unpoisoned %#lx\n", pfn);
                 return 0;
         }
 
@@ -1156,7 +1147,7 @@ int unpoison_memory(unsigned long pfn)
         if (!get_page_unless_zero(page)) {
                 if (TestClearPageHWPoison(p))
                         atomic_long_sub(nr_pages, &mce_bad_pages);
-                pr_debug("MCE: Software-unpoisoned free page %#lx\n", pfn);
+                pr_info("MCE: Software-unpoisoned free page %#lx\n", pfn);
                 return 0;
         }
 
@@ -1168,7 +1159,7 @@ int unpoison_memory(unsigned long pfn)
          * the free buddy page pool.
          */
         if (TestClearPageHWPoison(page)) {
-                pr_debug("MCE: Software-unpoisoned page %#lx\n", pfn);
+                pr_info("MCE: Software-unpoisoned page %#lx\n", pfn);
                 atomic_long_sub(nr_pages, &mce_bad_pages);
                 freeit = 1;
         }
@@ -1217,12 +1208,12 @@ static int get_any_page(struct page *p, unsigned long pfn, int flags)
         set_migratetype_isolate(p);
         if (!get_page_unless_zero(compound_head(p))) {
                 if (is_free_buddy_page(p)) {
-                        pr_debug("get_any_page: %#lx free buddy page\n", pfn);
+                        pr_info("get_any_page: %#lx free buddy page\n", pfn);
                         /* Set hwpoison bit while page is still isolated */
                         SetPageHWPoison(p);
                         ret = 0;
                 } else {
-                        pr_debug("get_any_page: %#lx: unknown zero refcount page type %lx\n",
+                        pr_info("get_any_page: %#lx: unknown zero refcount page type %lx\n",
                                 pfn, p->flags);
                         ret = -EIO;
                 }
@@ -1288,7 +1279,7 @@ int soft_offline_page(struct page *page, int flags)
                         goto done;
         }
         if (!PageLRU(page)) {
-                pr_debug("soft_offline: %#lx: unknown non LRU page type %lx\n",
+                pr_info("soft_offline: %#lx: unknown non LRU page type %lx\n",
                                 pfn, page->flags);
                 return -EIO;
         }
@@ -1302,7 +1293,7 @@ int soft_offline_page(struct page *page, int flags)
         if (PageHWPoison(page)) {
                 unlock_page(page);
                 put_page(page);
-                pr_debug("soft offline: %#lx page already poisoned\n", pfn);
+                pr_info("soft offline: %#lx page already poisoned\n", pfn);
                 return -EBUSY;
         }
 
@@ -1323,7 +1314,7 @@ int soft_offline_page(struct page *page, int flags)
         put_page(page);
         if (ret == 1) {
                 ret = 0;
-                pr_debug("soft_offline: %#lx: invalidated\n", pfn);
+                pr_info("soft_offline: %#lx: invalidated\n", pfn);
                 goto done;
         }
 
@@ -1339,13 +1330,13 @@ int soft_offline_page(struct page *page, int flags)
                 list_add(&page->lru, &pagelist);
                 ret = migrate_pages(&pagelist, new_page, MPOL_MF_MOVE_ALL, 0);
                 if (ret) {
-                        pr_debug("soft offline: %#lx: migration failed %d, type %lx\n",
+                        pr_info("soft offline: %#lx: migration failed %d, type %lx\n",
                                 pfn, ret, page->flags);
                         if (ret > 0)
                                 ret = -EIO;
                 }
         } else {
-                pr_debug("soft offline: %#lx: isolation failed: %d, page count %d, type %lx\n",
+                pr_info("soft offline: %#lx: isolation failed: %d, page count %d, type %lx\n",
                                 pfn, ret, page_count(page), page->flags);
         }
         if (ret)