2016-03-08 19:16:24

by Davidlohr Bueso

Subject: Re: [PATCH 09/18] ipc, shm: make shmem attach/detach wait for mmap_sem killable

On Mon, 29 Feb 2016, Michal Hocko wrote:

>From: Michal Hocko <[email protected]>
>
>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: Davidlohr Bueso <[email protected]>
>Cc: Hugh Dickins <[email protected]>
>Signed-off-by: Michal Hocko <[email protected]>

I have no objection to this perse, just one comment below.

Acked-by: Davidlohr Bueso <[email protected]>

>---
> ipc/shm.c | 9 +++++++--
> 1 file changed, 7 insertions(+), 2 deletions(-)
>
>diff --git a/ipc/shm.c b/ipc/shm.c
>index 331fc1b0b3c7..b8cfa05940d2 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 = -EINVAL;
>+ goto out_fput;
>+ }

This should be EINTR, no?

Thanks,
Davidlohr

>+
> 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
>--
>2.7.0
>

2016-03-09 10:17:05

by Michal Hocko

Subject: Re: [PATCH 09/18] ipc, shm: make shmem attach/detach wait for mmap_sem killable

On Tue 08-03-16 11:15:50, Davidlohr Bueso wrote:
> On Mon, 29 Feb 2016, Michal Hocko wrote:
>
> >From: Michal Hocko <[email protected]>
> >
> >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: Davidlohr Bueso <[email protected]>
> >Cc: Hugh Dickins <[email protected]>
> >Signed-off-by: Michal Hocko <[email protected]>
>
> I have no objection to this perse, just one comment below.
>
> Acked-by: Davidlohr Bueso <[email protected]>

Thanks!

[...]
> >- down_write(&current->mm->mmap_sem);
> >+ if (down_write_killable(&current->mm->mmap_sem)) {
> >+ err = -EINVAL;
> >+ goto out_fput;
> >+ }
>
> This should be EINTR, no?

Of course. Thanks for catching that.
--
Michal Hocko
SUSE Labs