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

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

[David Jeffery]

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 <djeffery@redhat.com>
---
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;
 }

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

[Trond Myklebust]

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 <djeffery@redhat.com>
> ---
> 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
trond.myklebust@primarydata.com