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    SubjectRe: [PATCH] ipc, shm: make shmem attach/detach wait for mmap_sem killable
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    On 03/09/2016 11:19 AM, Michal Hocko wrote:
    > From: Michal Hocko <mhocko@suse.com>
    >
    > shmat and shmdt rely on mmap_sem for write. If the waiting task
    > gets killed by the oom killer it would block oom_reaper from
    > asynchronous address space reclaim and reduce the chances of timely
    > OOM resolving. Wait for the lock in the killable mode and return with
    > EINTR if the task got killed while waiting.
    >
    > Cc: Hugh Dickins <hughd@google.com>
    > Signed-off-by: Michal Hocko <mhocko@suse.com>
    > Acked-by: Davidlohr Bueso <dave@stgolabs.net>

    Acked-by: Vlastimil Babka <vbabka@suse.cz>

    > ---
    > ipc/shm.c | 9 +++++++--
    > 1 file changed, 7 insertions(+), 2 deletions(-)
    >
    > diff --git a/ipc/shm.c b/ipc/shm.c
    > index 331fc1b0b3c7..13282510bc0d 100644
    > --- a/ipc/shm.c
    > +++ b/ipc/shm.c
    > @@ -1200,7 +1200,11 @@ long do_shmat(int shmid, char __user *shmaddr, int shmflg, ulong *raddr,
    > if (err)
    > goto out_fput;
    >
    > - down_write(&current->mm->mmap_sem);
    > + if (down_write_killable(&current->mm->mmap_sem)) {
    > + err = -EINTR;
    > + goto out_fput;
    > + }
    > +
    > if (addr && !(shmflg & SHM_REMAP)) {
    > err = -EINVAL;
    > if (addr + size < addr)
    > @@ -1271,7 +1275,8 @@ SYSCALL_DEFINE1(shmdt, char __user *, shmaddr)
    > if (addr & ~PAGE_MASK)
    > return retval;
    >
    > - down_write(&mm->mmap_sem);
    > + if (down_write_killable(&mm->mmap_sem))
    > + return -EINTR;
    >
    > /*
    > * This function tries to be smart and unmap shm segments that
    >

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