2014-08-05 15:19:42

by David Jeffery

Subject: [PATCH] nfs: Don't busy-wait on SIGKILL in __nfs_iocounter_wait

If a SIGKILL is sent to a task waiting in __nfs_iocounter_wait,
it will busy-wait or soft lockup in its while loop.
nfs_wait_bit_killable won't sleep, and the loop won't exit on
the error return.

Stop the busy-wait by breaking out of the loop when
nfs_wait_bit_killable returns an error.

Signed-off-by: David Jeffery <[email protected]>
---
I'm not completely confident this is the right solution. I
would like feedback if the intention was to break out of
this loop on error, or if we do need to wait here until
io_count hits zero and use something other than
nfs_wait_bit_killable to wait in case of SIGKILL.

pagelist.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/nfs/pagelist.c b/fs/nfs/pagelist.c
index 17fab89..f29a690 100644
--- a/fs/nfs/pagelist.c
+++ b/fs/nfs/pagelist.c
@@ -116,7 +116,7 @@ __nfs_iocounter_wait(struct nfs_io_counter *c)
if (atomic_read(&c->io_count) == 0)
break;
ret = nfs_wait_bit_killable(&c->flags);
- } while (atomic_read(&c->io_count) != 0);
+ } while (atomic_read(&c->io_count) != 0 && !ret);
finish_wait(wq, &q.wait);
return ret;
}

2014-08-21 00:29:25

by Trond Myklebust

Subject: Re: [PATCH] nfs: Don't busy-wait on SIGKILL in __nfs_iocounter_wait

On Tue, 2014-08-05 at 11:19 -0400, David Jeffery wrote:
> If a SIGKILL is sent to a task waiting in __nfs_iocounter_wait,
> it will busy-wait or soft lockup in its while loop.
> nfs_wait_bit_killable won't sleep, and the loop won't exit on
> the error return.
>
> Stop the busy-wait by breaking out of the loop when
> nfs_wait_bit_killable returns an error.
>
> Signed-off-by: David Jeffery <[email protected]>
> ---
> I'm not completely confident this is the right solution. I
> would like feedback if the intention was to break out of
> this loop on error, or if we do need to wait here until
> io_count hits zero and use something other than
> nfs_wait_bit_killable to wait in case of SIGKILL.
>
> pagelist.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/nfs/pagelist.c b/fs/nfs/pagelist.c
> index 17fab89..f29a690 100644
> --- a/fs/nfs/pagelist.c
> +++ b/fs/nfs/pagelist.c
> @@ -116,7 +116,7 @@ __nfs_iocounter_wait(struct nfs_io_counter *c)
> if (atomic_read(&c->io_count) == 0)
> break;
> ret = nfs_wait_bit_killable(&c->flags);
> - } while (atomic_read(&c->io_count) != 0);
> + } while (atomic_read(&c->io_count) != 0 && !ret);
> finish_wait(wq, &q.wait);
> return ret;
> }

Applied.
--
Trond Myklebust
Linux NFS client maintainer, PrimaryData
[email protected]