From: Tony Luck tony.luck@intel.com Subject: mm/memory-failure: use a mutex to avoid memory_failure() races

Patch series "mm,hwpoison: fix sending SIGBUS for Action Required MCE", v5.

I wrote this patchset to materialize what I think is the current allowable solution mentioned by the previous discussion [1]. I simply borrowed Tony's mutex patch and Aili's return code patch, then I queued another one to find error virtual address in the best effort manner. I know that this is not a perfect solution, but should work for some typical case.

[1]: https://lore.kernel.org/linux-mm/20210331192540.2141052f@alex-virtual-machin...

This patch (of 2):

There can be races when multiple CPUs consume poison from the same page. The first into memory_failure() atomically sets the HWPoison page flag and begins hunting for tasks that map this page. Eventually it invalidates those mappings and may send a SIGBUS to the affected tasks.

But while all that work is going on, other CPUs see a "success" return code from memory_failure() and so they believe the error has been handled and continue executing.

Fix by wrapping most of the internal parts of memory_failure() in a mutex.

[akpm@linux-foundation.org: make mf_mutex local to memory_failure()] Link: https://lkml.kernel.org/r/20210521030156.2612074-1-nao.horiguchi@gmail.com Link: https://lkml.kernel.org/r/20210521030156.2612074-2-nao.horiguchi@gmail.com Signed-off-by: Tony Luck tony.luck@intel.com Signed-off-by: Naoya Horiguchi naoya.horiguchi@nec.com Reviewed-by: Borislav Petkov bp@suse.de Reviewed-by: Oscar Salvador osalvador@suse.de Cc: Aili Yao yaoaili@kingsoft.com Cc: Andy Lutomirski luto@kernel.org Cc: Borislav Petkov bp@alien8.de Cc: David Hildenbrand david@redhat.com Cc: Jue Wang juew@google.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/memory-failure.c | 36 +++++++++++++++++++++++------------- 1 file changed, 23 insertions(+), 13 deletions(-)

--- a/mm/memory-failure.c~mm-memory-failure-use-a-mutex-to-avoid-memory_failure-races +++ a/mm/memory-failure.c @@ -1429,9 +1429,10 @@ int memory_failure(unsigned long pfn, in struct page *hpage; struct page *orig_head; struct dev_pagemap *pgmap; - int res; + int res = 0; unsigned long page_flags; bool retry = true; + static DEFINE_MUTEX(mf_mutex);

if (!sysctl_memory_failure_recovery) panic("Memory failure on page %lx", pfn); @@ -1449,13 +1450,18 @@ int memory_failure(unsigned long pfn, in return -ENXIO; }

+ mutex_lock(&mf_mutex); + try_again: - if (PageHuge(p)) - return memory_failure_hugetlb(pfn, flags); + if (PageHuge(p)) { + res = memory_failure_hugetlb(pfn, flags); + goto unlock_mutex; + } + if (TestSetPageHWPoison(p)) { pr_err("Memory failure: %#lx: already hardware poisoned\n", pfn); - return 0; + goto unlock_mutex; }

orig_head = hpage = compound_head(p); @@ -1488,17 +1494,19 @@ try_again: res = MF_FAILED; } action_result(pfn, MF_MSG_BUDDY, res); - return res == MF_RECOVERED ? 0 : -EBUSY; + res = res == MF_RECOVERED ? 0 : -EBUSY; } else { action_result(pfn, MF_MSG_KERNEL_HIGH_ORDER, MF_IGNORED); - return -EBUSY; + res = -EBUSY; } + goto unlock_mutex; }

if (PageTransHuge(hpage)) { if (try_to_split_thp_page(p, "Memory Failure") < 0) { action_result(pfn, MF_MSG_UNSPLIT_THP, MF_IGNORED); - return -EBUSY; + res = -EBUSY; + goto unlock_mutex; } VM_BUG_ON_PAGE(!page_count(p), p); } @@ -1522,7 +1530,7 @@ try_again: if (PageCompound(p) && compound_head(p) != orig_head) { action_result(pfn, MF_MSG_DIFFERENT_COMPOUND, MF_IGNORED); res = -EBUSY; - goto out; + goto unlock_page; }

/* @@ -1542,14 +1550,14 @@ try_again: num_poisoned_pages_dec(); unlock_page(p); put_page(p); - return 0; + goto unlock_mutex; } if (hwpoison_filter(p)) { if (TestClearPageHWPoison(p)) num_poisoned_pages_dec(); unlock_page(p); put_page(p); - return 0; + goto unlock_mutex; }

/* @@ -1573,7 +1581,7 @@ try_again: if (!hwpoison_user_mappings(p, pfn, flags, &p)) { action_result(pfn, MF_MSG_UNMAP_FAILED, MF_IGNORED); res = -EBUSY; - goto out; + goto unlock_page; }

/* @@ -1582,13 +1590,15 @@ try_again: if (PageLRU(p) && !PageSwapCache(p) && p->mapping == NULL) { action_result(pfn, MF_MSG_TRUNCATED_LRU, MF_IGNORED); res = -EBUSY; - goto out; + goto unlock_page; }

identify_page_state: res = identify_page_state(pfn, p, page_flags); -out: +unlock_page: unlock_page(p); +unlock_mutex: + mutex_unlock(&mf_mutex); return res; } EXPORT_SYMBOL_GPL(memory_failure); _