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SubjectRe: [PATCH] coredump: fix unfreezable coredumping task
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On 09/30/2016 11:50 AM, Andrey Ryabinin wrote:
> It could be not possible to freeze coredumping task when it waits
> for 'core_state->startup' completion, because threads are frozen
> in get_signal() before they got a chance to complete 'core_state->startup'.
>
> Use freezer_do_not_count() to tell freezer to ignore coredumping
> task while it waits for core_state->startup completion.
>
> Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
> Cc: stable@vger.kernel.org
> ---
> fs/coredump.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/fs/coredump.c b/fs/coredump.c
> index 281b768..eb9c92c 100644
> --- a/fs/coredump.c
> +++ b/fs/coredump.c
> @@ -1,6 +1,7 @@
> #include <linux/slab.h>
> #include <linux/file.h>
> #include <linux/fdtable.h>
> +#include <linux/freezer.h>
> #include <linux/mm.h>
> #include <linux/stat.h>
> #include <linux/fcntl.h>
> @@ -423,7 +424,9 @@ static int coredump_wait(int exit_code, struct core_state *core_state)
> if (core_waiters > 0) {
> struct core_thread *ptr;
>
> + freezer_do_not_count();
> wait_for_completion(&core_state->startup);
> + freezer_count();


As alternative to this we could introduce and use wait_for_completion_freezable():


---
fs/coredump.c | 2 +-
include/linux/completion.h | 1 +
kernel/sched/completion.c | 7 +++++++
3 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/fs/coredump.c b/fs/coredump.c
index 281b768..c145233 100644
--- a/fs/coredump.c
+++ b/fs/coredump.c
@@ -423,7 +423,7 @@ static int coredump_wait(int exit_code, struct core_state *core_state)
if (core_waiters > 0) {
struct core_thread *ptr;

- wait_for_completion(&core_state->startup);
+ wait_for_completion_freezable(&core_state->startup);
/*
* Wait for all the threads to become inactive, so that
* all the thread context (extended register state, like
diff --git a/include/linux/completion.h b/include/linux/completion.h
index 5d5aaae..8c2626f 100644
--- a/include/linux/completion.h
+++ b/include/linux/completion.h
@@ -89,6 +89,7 @@ static inline void reinit_completion(struct completion *x)
}

extern void wait_for_completion(struct completion *);
+extern void wait_for_completion_freezable(struct completion *);
extern void wait_for_completion_io(struct completion *);
extern int wait_for_completion_interruptible(struct completion *x);
extern int wait_for_completion_killable(struct completion *x);
diff --git a/kernel/sched/completion.c b/kernel/sched/completion.c
index 8d0f35d..0b9d1e3 100644
--- a/kernel/sched/completion.c
+++ b/kernel/sched/completion.c
@@ -11,6 +11,7 @@
* Waiting for completion is a typically sync point, but not an exclusion point.
*/

+#include <linux/freezer.h>
#include <linux/sched.h>
#include <linux/completion.h>

@@ -123,6 +124,12 @@ void __sched wait_for_completion(struct completion *x)
}
EXPORT_SYMBOL(wait_for_completion);

+void __sched wait_for_completion_freezable(struct completion *x)
+{
+ __wait_for_common(x, freezable_schedule_timeout,
+ MAX_SCHEDULE_TIMEOUT, TASK_UNINTERRUPTIBLE);
+}
+
/**
* wait_for_completion_timeout: - waits for completion of a task (w/timeout)
* @x: holds the state of this particular completion
--
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