Re: [PATCH] mm,hwpoison: return -EBUSY when page already poisoned

Luck, Tony
2021-03-05T22:12:22Z

This whole page table walking patch is trying to work around the
races caused by multiple calls to memory_failure() for the same
page.

Maybe better to just avoid the races. The comment right above
memory_failure says:

* Must run in process context (e.g. a work queue) with interrupts
* enabled and no spinlocks hold.

So it should be safe to grab and hold a mutex. See patch below.

-Tony

commit 8dd0dbe7d595e02647e9c2c76c03341a9f6bd7b9
Author: Tony Luck <tony.luck@intel.com>
Date: Fri Mar 5 10:40:48 2021 -0800

Use a mutex to avoid memory_failure() races

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 24210c9bd843..c1509f4b565e 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -1381,6 +1381,8 @@ static int memory_failure_dev_pagemap(unsigned long pfn, int flags,
return rc;
}

+static DEFINE_MUTEX(mf_mutex);
+
/**
* memory_failure - Handle memory failure of a page.
* @pfn: Page Number of the corrupted page
@@ -1424,12 +1426,18 @@ int memory_failure(unsigned long pfn, int flags)
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 out2;
+ }
+
if (TestSetPageHWPoison(p)) {
pr_err("Memory failure: %#lx: already hardware poisoned\n",
pfn);
+ mutex_unlock(&mf_mutex);
return 0;
}

@@ -1463,9 +1471,11 @@ int memory_failure(unsigned long pfn, int flags)
res = MF_FAILED;
}
action_result(pfn, MF_MSG_BUDDY, res);
+ mutex_unlock(&mf_mutex);
return res == MF_RECOVERED ? 0 : -EBUSY;
} else {
action_result(pfn, MF_MSG_KERNEL_HIGH_ORDER, MF_IGNORED);
+ mutex_unlock(&mf_mutex);
return -EBUSY;
}
}
@@ -1473,6 +1483,7 @@ int memory_failure(unsigned long pfn, int flags)
if (PageTransHuge(hpage)) {
if (try_to_split_thp_page(p, "Memory Failure") < 0) {
action_result(pfn, MF_MSG_UNSPLIT_THP, MF_IGNORED);
+ mutex_unlock(&mf_mutex);
return -EBUSY;
}
VM_BUG_ON_PAGE(!page_count(p), p);
@@ -1517,6 +1528,7 @@ int memory_failure(unsigned long pfn, int flags)
num_poisoned_pages_dec();
unlock_page(p);
put_page(p);
+ mutex_unlock(&mf_mutex);
return 0;
}
if (hwpoison_filter(p)) {
@@ -1524,6 +1536,7 @@ int memory_failure(unsigned long pfn, int flags)
num_poisoned_pages_dec();
unlock_page(p);
put_page(p);
+ mutex_unlock(&mf_mutex);
return 0;
}

@@ -1559,6 +1572,8 @@ int memory_failure(unsigned long pfn, int flags)
res = identify_page_state(pfn, p, page_flags);
out:
unlock_page(p);
+out2:
+ mutex_unlock(&mf_mutex);
return res;
}
EXPORT_SYMBOL_GPL(memory_failure);