lkml.org 
[lkml]   [2021]   [Feb]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH] mm,hwpoison: return -EBUSY when page already poisoned
    On Wed, 24 Feb 2021 11:31:55 +0100
    Oscar Salvador <osalvador@suse.de> wrote:


    > I have some questions:
    >
    > > 1.When LCME is enabled, and there are two processes A && B running on
    > > different core X && Y separately, which will access one same page, then
    > > the page corrupted when process A access it, a MCE will be rasied to
    > > 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?

    I am not sure whether this case will happen when !LMCE, when I realized this place may be an issue
    I tried to reproduce it and my configuration is LMCE enabled.

    > > 2.Then B access the page and trigger another MCE to core Y, it will also
    > > do error process, it will see TestSetPageHWPoison be true, and 0 is
    > > 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.

    Yes, I think after the recovery jod is finished, other processes still access the page
    will meet a page fault and error will be returned;

    > >
    > > 3.The kill_me_maybe will check the return:
    > >
    > > 1244 static void kill_me_maybe(struct callback_head *cb)
    > > 1245 {
    > >
    > > 1254 if (!memory_failure(p->mce_addr >> PAGE_SHIFT, flags) &&
    > > 1255 !(p->mce_kflags & MCE_IN_KERNEL_COPYIN)) {
    > > 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.
    >
    This set_mce_nospec() is not proper when the recovery job is on the fly. In my test
    this function failed.

    > 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.
    >
    What I care is the process B triggered the error again after process A,
    I don't know how it return and proceed.

    > So with your change, process B will be sent a SIGBUG, while process A is still
    > handling the MCE, right?

    Right!

    > > p->mce_whole_page);
    > > 1257 sync_core();
    > > 1258 return;
    > > 1259 }
    > >
    > > 1267 }
    > >
    > > 4. The error process for B will end, and may nothing happened if
    > > kill-early is not set, We may let the wrong data go into effect.
    > >
    > > For other cases which care the return value of memory_failure() should
    > > check why they want to process a memory error which have already been
    > > processed. This behavior seems reasonable.
    > >
    > > In kill_me_maybe, log the fact about the memory may not recovered, and
    > > we will kill the related process.
    > >
    > > Signed-off-by: Aili Yao <yaoaili@kingsoft.com>
    > > ---
    > > arch/x86/kernel/cpu/mce/core.c | 2 ++
    > > mm/memory-failure.c | 4 ++--
    > > 2 files changed, 4 insertions(+), 2 deletions(-)
    > >
    > > diff --git a/arch/x86/kernel/cpu/mce/core.c b/arch/x86/kernel/cpu/mce/core.c
    > > index e133ce1e562b..db4afc5bf15a 100644
    > > --- a/arch/x86/kernel/cpu/mce/core.c
    > > +++ b/arch/x86/kernel/cpu/mce/core.c
    > > @@ -1259,6 +1259,8 @@ static void kill_me_maybe(struct callback_head *cb)
    > > }
    > >
    > > if (p->mce_vaddr != (void __user *)-1l) {
    > > + pr_err("Memory error may not recovered: %#lx: Sending SIGBUS to %s:%d due to hardware memory corruption\n",
    > > + p->mce_addr >> PAGE_SHIFT, p->comm, p->pid);
    > > force_sig_mceerr(BUS_MCEERR_AR, p->mce_vaddr, PAGE_SHIFT);
    > > } else {
    > > pr_err("Memory error not recovered");
    > > diff --git a/mm/memory-failure.c b/mm/memory-failure.c
    > > index e9481632fcd1..06f006174b8c 100644
    > > --- a/mm/memory-failure.c
    > > +++ b/mm/memory-failure.c
    > > @@ -1224,7 +1224,7 @@ static int memory_failure_hugetlb(unsigned long pfn, int flags)
    > > if (TestSetPageHWPoison(head)) {
    > > pr_err("Memory failure: %#lx: already hardware poisoned\n",
    > > pfn);
    > > - return 0;
    > > + 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).
    >

    @David:

    I checked the code again, and find a few places will care the exact return value, like:

    1: drivers/base/memory.c:483: ret = memory_failure(pfn, 0);
    This is for hard page offline, I see the code in mcelog:
    static void offline_action(struct mempage *mp, u64 addr)
    {
    if (offline <= OFFLINE_ACCOUNT)
    return;
    Lprintf("Offlining page %llx\n", addr);
    if (memory_offline(addr) < 0) {
    Lprintf("Offlining page %llx failed: %s\n", addr, strerror(errno));
    mp->offlined = PAGE_OFFLINE_FAILED;
    } else
    mp->offlined = PAGE_OFFLINE;
    }
    I think return an negative value will be more proper? As the related killing function may not be performed, and we can't say
    it's a success operation?

    2:mm/hwpoison-inject.c:51: return memory_failure(pfn, 0);
    mm/madvise.c:910: ret = memory_failure(pfn, MF_COUNT_INCREASED);

    These two cases are mainly for error injections, I checked the test codes, mostly it only care if the value is 0 or < 0;
    I do the related test, normally it work well, but for stress test, sometimes in some case, I do meet some fail cases along with the -EBUSY return.
    I will dig more.

    Other place will only care if the return value is 0. or just ignore it.

    Hi naoya, what's your opnion for this possible issue, I need your inputs!

    Thanks
    Aili Yao

    \
     
     \ /
      Last update: 2021-02-25 04:44    [W:2.333 / U:0.052 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site