Linux-mm Archive on lore.kernel.org
 help / color / Atom feed
WARNING: multiple messages refer to this Message-ID
From: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
To: Dan Williams <dan.j.williams@intel.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>
Cc: Jane Chu <jane.chu@oracle.com>,
	linux-nvdimm <linux-nvdimm@lists.01.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: [PATCH] mm: hwpoison: use do_send_sig_info() instead of force_sig() (Re: PMEM error-handling forces SIGKILL causes kernel panic)
Date: Wed, 16 Jan 2019 09:30:46 +0000
Message-ID: <20190116093046.GA29835@hori1.linux.bs1.fc.nec.co.jp> (raw)
In-Reply-To: <20190111081401.GA5080@hori1.linux.bs1.fc.nec.co.jp>

[ CCed Andrew and linux-mm ]

On Fri, Jan 11, 2019 at 08:14:02AM +0000, Horiguchi Naoya(^[$BKY8}^[(B ^[$BD>Li^[(B) wrote:
> Hi Dan, Jane,
> 
> Thanks for the report.
> 
> On Wed, Jan 09, 2019 at 03:49:32PM -0800, Dan Williams wrote:
> > [ switch to text mail, add lkml and Naoya ]
> > 
> > On Wed, Jan 9, 2019 at 12:19 PM Jane Chu <jane.chu@oracle.com> wrote:
> ...
> > > 3. The hardware consists the latest revision CPU and Intel NVDIMM, we suspected
> > >    the CPU faulty because it generated MCE over PMEM UE in a unlikely high
> > >    rate for any reasonable NVDIMM (like a few per 24hours).
> > >
> > > After swapping the CPU, the problem stopped reproducing.
> > >
> > > But one could argue that perhaps the faulty CPU exposed a small race window
> > > from collect_procs() to unmap_mapping_range() and to kill_procs(), hence
> > > caught the kernel  PMEM error handler off guard.
> > 
> > There's definitely a race, and the implementation is buggy as can be
> > seen in __exit_signal:
> > 
> >         sighand = rcu_dereference_check(tsk->sighand,
> >                                         lockdep_tasklist_lock_is_held());
> >         spin_lock(&sighand->siglock);
> > 
> > ...the memory-failure path needs to hold the proper locks before it
> > can assume that de-referencing tsk->sighand is valid.
> > 
> > > Also note, the same workload on the same faulty CPU were run on Linux prior to
> > > the 4.19 PMEM error handling and did not encounter kernel crash, probably because
> > > the prior HWPOISON handler did not force SIGKILL?
> > 
> > Before 4.19 this test should result in a machine-check reboot, not
> > much better than a kernel crash.
> > 
> > > Should we not to force the SIGKILL, or find a way to close the race window?
> > 
> > The race should be closed by holding the proper tasklist and rcu read lock(s).
> 
> This reasoning and proposal sound right to me. I'm trying to reproduce
> this race (for non-pmem case,) but no luck for now. I'll investigate more.

I wrote/tested a patch for this issue.
I think that switching signal API effectively does proper locking.

Thanks,
Naoya Horiguchi
---
>From 16dbf6105ff4831f73276d79d5df238ab467de76 Mon Sep 17 00:00:00 2001
From: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Date: Wed, 16 Jan 2019 16:59:27 +0900
Subject: [PATCH] mm: hwpoison: use do_send_sig_info() instead of force_sig()

Currently memory_failure() is racy against process's exiting,
which results in kernel crash by null pointer dereference.

The root cause is that memory_failure() uses force_sig() to forcibly
kill asynchronous (meaning not in the current context) processes.  As
discussed in thread https://lkml.org/lkml/2010/6/8/236 years ago for
OOM fixes, this is not a right thing to do.  OOM solves this issue by
using do_send_sig_info() as done in commit d2d393099de2 ("signal:
oom_kill_task: use SEND_SIG_FORCED instead of force_sig()"), so this
patch is suggesting to do the same for hwpoison.  do_send_sig_info()
properly accesses to siglock with lock_task_sighand(), so is free from
the reported race.

I confirmed that the reported bug reproduces with inserting some delay
in kill_procs(), and it never reproduces with this patch.

Note that memory_failure() can send another type of signal using
force_sig_mceerr(), and the reported race shouldn't happen on it
because force_sig_mceerr() is called only for synchronous processes
(i.e. BUS_MCEERR_AR happens only when some process accesses to the
corrupted memory.)

Reported-by: Jane Chu <jane.chu@oracle.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: stable@vger.kernel.org
Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
---
 mm/memory-failure.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 7c72f2a95785..831be5ff5f4d 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -372,7 +372,8 @@ static void kill_procs(struct list_head *to_kill, int forcekill, bool fail,
 			if (fail || tk->addr_valid == 0) {
 				pr_err("Memory failure: %#lx: forcibly killing %s:%d because of failure to unmap corrupted page\n",
 				       pfn, tk->tsk->comm, tk->tsk->pid);
-				force_sig(SIGKILL, tk->tsk);
+				do_send_sig_info(SIGKILL, SEND_SIG_PRIV,
+						 tk->tsk, PIDTYPE_PID);
 			}
 
 			/*
-- 
2.7.5

From: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
To: Dan Williams <dan.j.williams@intel.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>
Cc: Jane Chu <jane.chu@oracle.com>,
	linux-nvdimm <linux-nvdimm@lists.01.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: [PATCH] mm: hwpoison: use do_send_sig_info() instead of force_sig() (Re: PMEM error-handling forces SIGKILL causes kernel panic)
Date: Wed, 16 Jan 2019 09:30:46 +0000
Message-ID: <20190116093046.GA29835@hori1.linux.bs1.fc.nec.co.jp> (raw)
Message-ID: <20190116093046.Sk51uHsImk990fHMlLWWHELQmAkTQxE2ChFUeT_lx2k@z> (raw)
In-Reply-To: <20190111081401.GA5080@hori1.linux.bs1.fc.nec.co.jp>

[ CCed Andrew and linux-mm ]

On Fri, Jan 11, 2019 at 08:14:02AM +0000, Horiguchi Naoya(^[$BKY8}^[(B ^[$BD>Li^[(B) wrote:
> Hi Dan, Jane,
> 
> Thanks for the report.
> 
> On Wed, Jan 09, 2019 at 03:49:32PM -0800, Dan Williams wrote:
> > [ switch to text mail, add lkml and Naoya ]
> > 
> > On Wed, Jan 9, 2019 at 12:19 PM Jane Chu <jane.chu@oracle.com> wrote:
> ...
> > > 3. The hardware consists the latest revision CPU and Intel NVDIMM, we suspected
> > >    the CPU faulty because it generated MCE over PMEM UE in a unlikely high
> > >    rate for any reasonable NVDIMM (like a few per 24hours).
> > >
> > > After swapping the CPU, the problem stopped reproducing.
> > >
> > > But one could argue that perhaps the faulty CPU exposed a small race window
> > > from collect_procs() to unmap_mapping_range() and to kill_procs(), hence
> > > caught the kernel  PMEM error handler off guard.
> > 
> > There's definitely a race, and the implementation is buggy as can be
> > seen in __exit_signal:
> > 
> >         sighand = rcu_dereference_check(tsk->sighand,
> >                                         lockdep_tasklist_lock_is_held());
> >         spin_lock(&sighand->siglock);
> > 
> > ...the memory-failure path needs to hold the proper locks before it
> > can assume that de-referencing tsk->sighand is valid.
> > 
> > > Also note, the same workload on the same faulty CPU were run on Linux prior to
> > > the 4.19 PMEM error handling and did not encounter kernel crash, probably because
> > > the prior HWPOISON handler did not force SIGKILL?
> > 
> > Before 4.19 this test should result in a machine-check reboot, not
> > much better than a kernel crash.
> > 
> > > Should we not to force the SIGKILL, or find a way to close the race window?
> > 
> > The race should be closed by holding the proper tasklist and rcu read lock(s).
> 
> This reasoning and proposal sound right to me. I'm trying to reproduce
> this race (for non-pmem case,) but no luck for now. I'll investigate more.

I wrote/tested a patch for this issue.
I think that switching signal API effectively does proper locking.

Thanks,
Naoya Horiguchi
---
From 16dbf6105ff4831f73276d79d5df238ab467de76 Mon Sep 17 00:00:00 2001
From: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Date: Wed, 16 Jan 2019 16:59:27 +0900
Subject: [PATCH] mm: hwpoison: use do_send_sig_info() instead of force_sig()

Currently memory_failure() is racy against process's exiting,
which results in kernel crash by null pointer dereference.

The root cause is that memory_failure() uses force_sig() to forcibly
kill asynchronous (meaning not in the current context) processes.  As
discussed in thread https://lkml.org/lkml/2010/6/8/236 years ago for
OOM fixes, this is not a right thing to do.  OOM solves this issue by
using do_send_sig_info() as done in commit d2d393099de2 ("signal:
oom_kill_task: use SEND_SIG_FORCED instead of force_sig()"), so this
patch is suggesting to do the same for hwpoison.  do_send_sig_info()
properly accesses to siglock with lock_task_sighand(), so is free from
the reported race.

I confirmed that the reported bug reproduces with inserting some delay
in kill_procs(), and it never reproduces with this patch.

Note that memory_failure() can send another type of signal using
force_sig_mceerr(), and the reported race shouldn't happen on it
because force_sig_mceerr() is called only for synchronous processes
(i.e. BUS_MCEERR_AR happens only when some process accesses to the
corrupted memory.)

Reported-by: Jane Chu <jane.chu@oracle.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: stable@vger.kernel.org
Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
---
 mm/memory-failure.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 7c72f2a95785..831be5ff5f4d 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -372,7 +372,8 @@ static void kill_procs(struct list_head *to_kill, int forcekill, bool fail,
 			if (fail || tk->addr_valid == 0) {
 				pr_err("Memory failure: %#lx: forcibly killing %s:%d because of failure to unmap corrupted page\n",
 				       pfn, tk->tsk->comm, tk->tsk->pid);
-				force_sig(SIGKILL, tk->tsk);
+				do_send_sig_info(SIGKILL, SEND_SIG_PRIV,
+						 tk->tsk, PIDTYPE_PID);
 			}
 
 			/*
-- 
2.7.5



       reply index

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <e3c4c0e0-1434-4353-b893-2973c04e7ff7@oracle.com>
     [not found] ` <CAPcyv4j67n6H7hD6haXJqysbaauci4usuuj5c+JQ7VQBGngO1Q@mail.gmail.com>
     [not found]   ` <20190111081401.GA5080@hori1.linux.bs1.fc.nec.co.jp>
2019-01-16  9:30     ` Naoya Horiguchi [this message]
2019-01-16  9:30       ` Naoya Horiguchi
2019-01-16 16:55       ` Dan Williams
2019-01-16 16:55         ` Dan Williams
2019-01-16 17:20         ` Jane Chu
2019-01-16 17:20           ` Jane Chu
2019-01-16 17:56       ` Jane Chu
2019-01-16 23:32         ` Naoya Horiguchi
2019-01-17  1:07           ` Jane Chu
2019-01-17  9:44             ` William Kucharski

Reply instructions:

You may reply publically to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20190116093046.GA29835@hori1.linux.bs1.fc.nec.co.jp \
    --to=n-horiguchi@ah.jp.nec.com \
    --cc=akpm@linux-foundation.org \
    --cc=dan.j.williams@intel.com \
    --cc=jane.chu@oracle.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=linux-nvdimm@lists.01.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Linux-mm Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-mm/0 linux-mm/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-mm linux-mm/ https://lore.kernel.org/linux-mm \
		linux-mm@kvack.org linux-mm@archiver.kernel.org
	public-inbox-index linux-mm


Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kvack.linux-mm


AGPL code for this site: git clone https://public-inbox.org/ public-inbox