Re: [PATCH] mm,hwpoison: return -EBUSY when page already poisoned
From: Oscar Salvador
Date: Wed Feb 24 2021 - 05:32:47 EST
On Wed, Feb 24, 2021 at 03:16:19PM +0800, Aili Yao wrote:
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When the page is already poisoned, another memory_failure() call in the
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same page now return 0, meaning OK. For nested memory mce handling, this
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behavior may lead real serious problem, Example:
I have some questions:
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1.When LCME is enabled, and there are two processes A && B running on
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different core X && Y separately, which will access one same page, then
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the page corrupted when process A access it, a MCE will be rasied to
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core X and the error process is just underway.
When !LMCE, that is not a problem because new MCE needs to wait for the ongoing MCE?
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2.Then B access the page and trigger another MCE to core Y, it will also
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do error process, it will see TestSetPageHWPoison be true, and 0 is
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returned.
For non-nested calls, that is no problem because the page will be taken out
of business(unmapped from the processes), right? So no more MCE are possible.
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3.The kill_me_maybe will check the return:
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1244 static void kill_me_maybe(struct callback_head *cb)
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1245 {
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1254 if (!memory_failure(p->mce_addr >> PAGE_SHIFT, flags) &&
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1255 !(p->mce_kflags & MCE_IN_KERNEL_COPYIN)) {
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1256 set_mce_nospec(p->mce_addr >> PAGE_SHIFT,
So, IIUC, in case of a LMCE nested call, the second MCE will reach here.
set_mce_nospec() will either mark the underlying page as not mapped/cached.
Should not have memory_failure()->hwpoison_user_mappings() unmapped the page
from both process A and B? Or this is in case the ongoing MCE(process A) has
not still unmapped anything, so process B can still access this page.
So with your change, process B will be sent a SIGBUG, while process A is still
handling the MCE, right?
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p->mce_whole_page);
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1257 sync_core();
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1258 return;
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1259 }
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1267 }
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4. The error process for B will end, and may nothing happened if
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kill-early is not set, We may let the wrong data go into effect.
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For other cases which care the return value of memory_failure() should
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check why they want to process a memory error which have already been
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processed. This behavior seems reasonable.
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In kill_me_maybe, log the fact about the memory may not recovered, and
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we will kill the related process.
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Signed-off-by: Aili Yao <yaoaili@xxxxxxxxxxxx>
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---
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arch/x86/kernel/cpu/mce/core.c | 2 ++
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mm/memory-failure.c | 4 ++--
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2 files changed, 4 insertions(+), 2 deletions(-)
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diff --git a/arch/x86/kernel/cpu/mce/core.c b/arch/x86/kernel/cpu/mce/core.c
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index e133ce1e562b..db4afc5bf15a 100644
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--- a/arch/x86/kernel/cpu/mce/core.c
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+++ b/arch/x86/kernel/cpu/mce/core.c
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@@ -1259,6 +1259,8 @@ static void kill_me_maybe(struct callback_head *cb)
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}
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if (p->mce_vaddr != (void __user *)-1l) {
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+ pr_err("Memory error may not recovered: %#lx: Sending SIGBUS to %s:%d due to hardware memory corruption\n",
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+ p->mce_addr >> PAGE_SHIFT, p->comm, p->pid);
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force_sig_mceerr(BUS_MCEERR_AR, p->mce_vaddr, PAGE_SHIFT);
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} else {
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pr_err("Memory error not recovered");
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diff --git a/mm/memory-failure.c b/mm/memory-failure.c
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index e9481632fcd1..06f006174b8c 100644
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--- a/mm/memory-failure.c
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+++ b/mm/memory-failure.c
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@@ -1224,7 +1224,7 @@ static int memory_failure_hugetlb(unsigned long pfn, int flags)
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if (TestSetPageHWPoison(head)) {
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pr_err("Memory failure: %#lx: already hardware poisoned\n",
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pfn);
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- return 0;
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+ return -EBUSY;
As David said, madvise_inject_error() will start returning -EBUSY now in case
we madvise(MADV_HWPOISON) on an already hwpoisoned page.
AFAICS, memory_failure() can return 0, -Eerrors, and MF_XXX.
Would it make sense to unify that? That way we could declare error codes that
make somse sense (like MF_ALREADY_HWPOISONED).
--
Oscar Salvador
SUSE L3