On Mon, Jun 30, 2014 at 01:36:06PM -0400, Naoya Horiguchi wrote:
> > The patch below does not apply to the 3.4-stable tree.
> > If someone wants it applied there, or to any other stable or longterm
> > tree, then please email the backport, including the original git commit
> > id to <stable@xxxxxxxxxxxxxxx>.
>
> Yes, we have a conflict when we try to apply on stable-3.4. This is
> because the patch contains anon_vma_interval_tree_foreach() and
> vma_interval_tree_foreach() in the diff context, but these macros were
> introduced at 3.7, so we can make it applicable by simply changing
> the context lines to the older context lines.
>
> Here is the backport patch below, could you try this?
> # This patch depends on commit 74614de17db6 "mm/memory-failure.c: don't
> # let collect_procs() skip over processes for MF_ACTION_REQUIRED"
>
> Thanks,
> Naoya Horiguchi
> ---
> From: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
> Date: Mon, 30 Jun 2014 12:45:07 -0400
> Subject: [PATCH] mm/memory-failure.c: support use of a dedicated thread to
> handle SIGBUS(BUS_MCEERR_AO)
>
> commit 3ba08129e38437561df44c36b7ea9081185d5333 upstream.
>
> Currently memory error handler handles action optional errors in the
> deferred manner by default. And if a recovery aware application wants
> to handle it immediately, it can do it by setting PF_MCE_EARLY flag.
> However, such signal can be sent only to the main thread, so it's
> problematic if the application wants to have a dedicated thread to
> handler such signals.
>
> So this patch adds dedicated thread support to memory error handler. We
> have PF_MCE_EARLY flags for each thread separately, so with this patch
> AO signal is sent to the thread with PF_MCE_EARLY flag set, not the main
> thread. If you want to implement a dedicated thread, you call prctl()
> to set PF_MCE_EARLY on the thread.
>
> Memory error handler collects processes to be killed, so this patch lets
> it check PF_MCE_EARLY flag on each thread in the collecting routines.
>
> No behavioral change for all non-early kill cases.
>
> Tony said:
>
> : The old behavior was crazy - someone with a multithreaded process might
> : well expect that if they call prctl(PF_MCE_EARLY) in just one thread, then
> : that thread would see the SIGBUS with si_code = BUS_MCEERR_A0 - even if
> : that thread wasn't the main thread for the process.
>
> [n-horiguchi@xxxxxxxxxxxxx: resolved conflict for stable]
> [akpm@xxxxxxxxxxxxxxxxxxxx: coding-style fixes]
> Signed-off-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
> Reviewed-by: Tony Luck <tony.luck@xxxxxxxxx>
> Cc: Kamil Iskra <iskra@xxxxxxxxxxx>
> Cc: Andi Kleen <andi@xxxxxxxxxxxxxx>
> Cc: Borislav Petkov <bp@xxxxxxx>
> Cc: Chen Gong <gong.chen@xxxxxxxxxxxxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx> [3.2+]
> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> ---
> Documentation/vm/hwpoison.txt | 5 ++++
> mm/memory-failure.c | 55 +++++++++++++++++++++++++++++++++----------
> 2 files changed, 48 insertions(+), 12 deletions(-)
>
> diff --git a/Documentation/vm/hwpoison.txt b/Documentation/vm/hwpoison.txt
> index 550068466605..6ae89a9edf2a 100644
> --- a/Documentation/vm/hwpoison.txt
> +++ b/Documentation/vm/hwpoison.txt
> @@ -84,6 +84,11 @@ PR_MCE_KILL
> PR_MCE_KILL_EARLY: Early kill
> PR_MCE_KILL_LATE: Late kill
> PR_MCE_KILL_DEFAULT: Use system global default
> + Note that if you want to have a dedicated thread which handles
> + the SIGBUS(BUS_MCEERR_AO) on behalf of the process, you should
> + call prctl(PR_MCE_KILL_EARLY) on the designated thread. Otherwise,
> + the SIGBUS is sent to the main thread.
> +
> PR_MCE_KILL_GET
> return current mode
>
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index e88db79be1f0..ebe18360cf58 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -382,15 +382,44 @@ static void kill_procs(struct list_head *to_kill, int forcekill, int trapno,
> }
> }
>
> -static int task_early_kill(struct task_struct *tsk, int force_early)
> +/*
> + * Find a dedicated thread which is supposed to handle SIGBUS(BUS_MCEERR_AO)
> + * on behalf of the thread group. Return task_struct of the (first found)
> + * dedicated thread if found, and return NULL otherwise.
> + *
> + * We already hold read_lock(&tasklist_lock) in the caller, so we don't
> + * have to call rcu_read_lock/unlock() in this function.
> + */
> +static struct task_struct *find_early_kill_thread(struct task_struct *tsk)
> {
> + struct task_struct *t;
> +
> + for_each_thread(tsk, t)
> + if ((t->flags & PF_MCE_PROCESS) && (t->flags & PF_MCE_EARLY))
> + return t;
3.4-stable does not have for_each_thread() so this will not build
properly :(
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