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

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  Re: [PATCH 09/18] ipc, shm: make shmem attach/detach wait for  mmap_sem killable Davidlohr Bueso <dave@stgolabs.net> - 2016-03-08 20:20 +0100
    Re: [PATCH 09/18] ipc, shm: make shmem attach/detach wait for  mmap_sem killable Michal Hocko <mhocko@kernel.org> - 2016-03-09 11:20 +0100

#1353324 — 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 <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: Davidlohr Bueso <dave@stgolabs.net>
>Cc: Hugh Dickins <hughd@google.com>
>Signed-off-by: Michal Hocko <mhocko@suse.com>

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

Acked-by: Davidlohr Bueso <dave@stgolabs.net>

>---
> 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
>

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#1353940

On Tue 08-03-16 11:15:50, Davidlohr Bueso wrote:
> On Mon, 29 Feb 2016, 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: Davidlohr Bueso <dave@stgolabs.net>
> >Cc: Hugh Dickins <hughd@google.com>
> >Signed-off-by: Michal Hocko <mhocko@suse.com>
> 
> I have no objection to this perse, just one comment below.
> 
> Acked-by: Davidlohr Bueso <dave@stgolabs.net>

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

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