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    Subject[PATCH 3.16 224/306] coredump: fix unfreezable coredumping task
    3.16.40-rc1 review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Andrey Ryabinin <aryabinin@virtuozzo.com>

    commit 70d78fe7c8b640b5acfad56ad341985b3810998a upstream.

    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'.

    Inability to freeze a task during suspend will cause suspend to fail.
    Also CRIU uses cgroup freezer during dump operation. So with an
    unfreezable task the CRIU dump will fail because it waits for a
    transition from 'FREEZING' to 'FROZEN' state which will never happen.

    Use freezer_do_not_count() to tell freezer to ignore coredumping task
    while it waits for core_state->startup completion.

    Link: http://lkml.kernel.org/r/1475225434-3753-1-git-send-email-aryabinin@virtuozzo.com
    Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
    Acked-by: Pavel Machek <pavel@ucw.cz>
    Acked-by: Oleg Nesterov <oleg@redhat.com>
    Cc: Alexander Viro <viro@zeniv.linux.org.uk>
    Cc: Tejun Heo <tj@kernel.org>
    Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
    Cc: Michal Hocko <mhocko@kernel.org>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    fs/coredump.c | 3 +++
    1 file changed, 3 insertions(+)

    --- 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>
    @@ -385,7 +386,9 @@ static int coredump_wait(int exit_code,
    if (core_waiters > 0) {
    struct core_thread *ptr;

    + freezer_do_not_count();
    wait_for_completion(&core_state->startup);
    + freezer_count();
    /*
    * Wait for all the threads to become inactive, so that
    * all the thread context (extended register state, like
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