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Subject[PATCH 3.12 115/181] mm/memory-failure.c: support use of a dedicated thread to handle SIGBUS(BUS_MCEERR_AO)
Date
From: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>

3.12-stable review patch. If anyone has any objections, please let me know.

===============

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.

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Cc: Kamil Iskra <iskra@mcs.anl.gov>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Borislav Petkov <bp@suse.de>
Cc: Chen Gong <gong.chen@linux.jf.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
Documentation/vm/hwpoison.txt | 5 ++++
mm/memory-failure.c | 56 +++++++++++++++++++++++++++++++++----------
2 files changed, 48 insertions(+), 13 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 340fc9ae63bd..6e3f9c39bc22 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -384,15 +384,44 @@ 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;
+ return NULL;
+}
+
+/*
+ * Determine whether a given process is "early kill" process which expects
+ * to be signaled when some page under the process is hwpoisoned.
+ * Return task_struct of the dedicated thread (main thread unless explicitly
+ * specified) if the process is "early kill," and otherwise returns NULL.
+ */
+static struct task_struct *task_early_kill(struct task_struct *tsk,
+ int force_early)
{
+ struct task_struct *t;
if (!tsk->mm)
- return 0;
+ return NULL;
if (force_early)
- return 1;
- if (tsk->flags & PF_MCE_PROCESS)
- return !!(tsk->flags & PF_MCE_EARLY);
- return sysctl_memory_failure_early_kill;
+ return tsk;
+ t = find_early_kill_thread(tsk);
+ if (t)
+ return t;
+ if (sysctl_memory_failure_early_kill)
+ return tsk;
+ return NULL;
}

/*
@@ -414,16 +443,17 @@ static void collect_procs_anon(struct page *page, struct list_head *to_kill,
read_lock(&tasklist_lock);
for_each_process (tsk) {
struct anon_vma_chain *vmac;
+ struct task_struct *t = task_early_kill(tsk, force_early);

- if (!task_early_kill(tsk, force_early))
+ if (!t)
continue;
anon_vma_interval_tree_foreach(vmac, &av->rb_root,
pgoff, pgoff) {
vma = vmac->vma;
if (!page_mapped_in_vma(page, vma))
continue;
- if (vma->vm_mm == tsk->mm)
- add_to_kill(tsk, page, vma, to_kill, tkc);
+ if (vma->vm_mm == t->mm)
+ add_to_kill(t, page, vma, to_kill, tkc);
}
}
read_unlock(&tasklist_lock);
@@ -444,10 +474,10 @@ static void collect_procs_file(struct page *page, struct list_head *to_kill,
read_lock(&tasklist_lock);
for_each_process(tsk) {
pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
+ struct task_struct *t = task_early_kill(tsk, force_early);

- if (!task_early_kill(tsk, force_early))
+ if (!t)
continue;
-
vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff,
pgoff) {
/*
@@ -457,8 +487,8 @@ static void collect_procs_file(struct page *page, struct list_head *to_kill,
* Assume applications who requested early kill want
* to be informed of all such data corruptions.
*/
- if (vma->vm_mm == tsk->mm)
- add_to_kill(tsk, page, vma, to_kill, tkc);
+ if (vma->vm_mm == t->mm)
+ add_to_kill(t, page, vma, to_kill, tkc);
}
}
read_unlock(&tasklist_lock);
--
2.0.0


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