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From: Borislav Petkov <bp@alien8.de>
To: "Luck, Tony" <tony.luck@intel.com>
Cc: x86@kernel.org, Andrew Morton <akpm@linux-foundation.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Darren Hart <dvhart@infradead.org>,
	Andy Lutomirski <luto@kernel.org>,
	linux-kernel@vger.kernel.org, linux-edac@vger.kernel.org,
	linux-mm@kvack.org
Subject: Re: [PATCH v5] x86/mce: Avoid infinite loop for copy from user recovery
Date: Tue, 26 Jan 2021 12:03:14 +0100	[thread overview]
Message-ID: <20210126110314.GC6514@zn.tnic> (raw)
In-Reply-To: <20210125225509.GA7149@agluck-desk2.amr.corp.intel.com>

On Mon, Jan 25, 2021 at 02:55:09PM -0800, Luck, Tony wrote:
> And now I've changed it back to non-atomic (but keeping the
> slightly cleaner looking code style that I used for the atomic
> version).  This one also works for thousands of injections and
> recoveries.  Maybe take it now before it stops working again :-)

Hmm, so the only differences I see between your v4 and this are:

-@@ -1238,6 +1238,7 @@ static void __mc_scan_banks(struct mce *m, struct pt_regs *regs, struct mce *fin
+@@ -1238,6 +1238,9 @@ static void __mc_scan_banks(struct mce *m, struct pt_regs *regs, struct mce *fin
  
  static void kill_me_now(struct callback_head *ch)
  {
++	struct task_struct *p = container_of(ch, struct task_struct, mce_kill_me);
++
 +	p->mce_count = 0;
  	force_sig(SIGBUS);
  }

Could the container_of() macro have changed something?

Because we don't know yet (right?) why would it fail? Would it read
stale ->mce_count data? If so, then a barrier is missing somewhere.

Or what is the failure exactly?

Because if I take it now without us knowing what the issue is, it will
start failing somewhere - Murphy's our friend - and then we'll have to
deal with breaking people's boxes. Not fun.

The other difference is:

@@ -76,8 +71,10 @@ index 13d3f1cbda17..5460c146edb5 100644
 -	current->mce_kflags = m->kflags;
 -	current->mce_ripv = !!(m->mcgstatus & MCG_STATUS_RIPV);
 -	current->mce_whole_page = whole_page(m);
++	int count = ++current->mce_count;
++
 +	/* First call, save all the details */
-+	if (current->mce_count++ == 0) {
++	if (count == 1) {
 +		current->mce_addr = m->addr;
 +		current->mce_kflags = m->kflags;
 +		current->mce_ripv = !!(m->mcgstatus & MCG_STATUS_RIPV);

Hmm, a local variable and a pre-increment. Can that have an effect somehow?

> +	/* Ten is likley overkill. Don't expect more than two faults before task_work() */

Typo: likely.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette

  reply	other threads:[~2021-01-26 12:20 UTC|newest]

Thread overview: 50+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-08 22:22 [PATCH 0/2] Fix infinite machine check loop in futex_wait_setup() Tony Luck
2021-01-08 22:22 ` [PATCH 1/2] x86/mce: Avoid infinite loop for copy from user recovery Tony Luck
2021-01-08 22:22 ` [PATCH 2/2] futex, x86/mce: Avoid double machine checks Tony Luck
2021-01-08 22:47   ` Peter Zijlstra
2021-01-08 23:08     ` Luck, Tony
2021-01-08 23:14       ` Peter Zijlstra
2021-01-08 23:20         ` Luck, Tony
2021-01-11 21:44 ` [PATCH v2 0/3] Fix infinite machine check loop in futex_wait_setup() Tony Luck
2021-01-11 21:44   ` [PATCH v2 1/3] x86/mce: Avoid infinite loop for copy from user recovery Tony Luck
2021-01-11 22:11     ` Andy Lutomirski
2021-01-11 22:20       ` Luck, Tony
2021-01-12 17:00         ` Andy Lutomirski
2021-01-12 17:16           ` Luck, Tony
2021-01-12 17:21             ` Andy Lutomirski
2021-01-12 18:23               ` Luck, Tony
2021-01-12 18:57                 ` Andy Lutomirski
2021-01-12 20:52                   ` Luck, Tony
2021-01-12 22:04                     ` Andy Lutomirski
2021-01-13  1:50                       ` Luck, Tony
2021-01-13  4:15                         ` Andy Lutomirski
2021-01-13 10:00                           ` Borislav Petkov
2021-01-13 16:06                             ` Luck, Tony
2021-01-13 16:19                               ` Borislav Petkov
2021-01-13 16:32                                 ` Luck, Tony
2021-01-13 17:35                                   ` Borislav Petkov
2021-01-14 20:22     ` Borislav Petkov
2021-01-14 21:05       ` Luck, Tony
2021-01-11 21:44   ` [PATCH v2 2/3] x86/mce: Add new return value to get_user() for machine check Tony Luck
2021-01-11 21:44   ` [PATCH v2 3/3] futex, x86/mce: Avoid double machine checks Tony Luck
2021-01-14 17:22   ` [PATCH v2 0/3] Fix infinite machine check loop in futex_wait_setup() Andy Lutomirski
2021-01-15  0:38   ` [PATCH v3] x86/mce: Avoid infinite loop for copy from user recovery Tony Luck
2021-01-15 15:27     ` Borislav Petkov
2021-01-15 19:34       ` Luck, Tony
2021-01-15 20:51         ` [PATCH v4] " Luck, Tony
2021-01-15 23:23           ` Luck, Tony
2021-01-19 10:56             ` Borislav Petkov
2021-01-19 23:57               ` Luck, Tony
2021-01-20 12:18                 ` Borislav Petkov
2021-01-20 17:17                   ` Luck, Tony
2021-01-21 21:09                   ` Luck, Tony
2021-01-25 22:55                     ` [PATCH v5] " Luck, Tony
2021-01-26 11:03                       ` Borislav Petkov [this message]
2021-01-26 22:36                         ` Luck, Tony
2021-01-28 17:57                           ` Borislav Petkov
2021-02-01 18:58                             ` Luck, Tony
2021-02-02 11:01                               ` Borislav Petkov
2021-02-02 16:04                                 ` Luck, Tony
2021-02-02 21:06                                   ` Borislav Petkov
2021-02-02 22:12                                     ` Luck, Tony
2021-01-18 15:39         ` [PATCH v3] " Borislav Petkov

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