Hi Antony,

I think I may have a fix already lurking on my netfs-writeback branch for the
next merge window.  Can you try the attached?

David
---
Don't revert the I/O iterator before returning from p9_client_read_once().
netfslib doesn't require the reversion and nor doed 9P directory reading.

Make p9_client_read() use a temporary iterator to call down into
p9_client_read_once(), and advance that by the amount read.

Reported-by: Antony Antony <antony@phenome.org>
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Eric Van Hensbergen <ericvh@kernel.org>
cc: Latchesar Ionkov <lucho@ionkov.net>
cc: Dominique Martinet <asmadeus@codewreck.org>
cc: Christian Schoenebeck <linux_oss@crudebyte.com>
cc: v9fs@lists.linux.dev
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
---
 net/9p/client.c |   10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/net/9p/client.c b/net/9p/client.c
index 5cd94721d974..be59b0a94eaf 100644
--- a/net/9p/client.c
+++ b/net/9p/client.c
@@ -1519,13 +1519,15 @@ p9_client_read(struct p9_fid *fid, u64 offset, struct iov_iter *to, int *err)
 	*err = 0;
 
 	while (iov_iter_count(to)) {
+		struct iov_iter tmp = *to;
 		int count;
 
-		count = p9_client_read_once(fid, offset, to, err);
+		count = p9_client_read_once(fid, offset, &tmp, err);
 		if (!count || *err)
 			break;
 		offset += count;
 		total += count;
+		iov_iter_advance(to, count);
 	}
 	return total;
 }
@@ -1567,16 +1569,12 @@ p9_client_read_once(struct p9_fid *fid, u64 offset, struct iov_iter *to,
 	}
 	if (IS_ERR(req)) {
 		*err = PTR_ERR(req);
-		if (!non_zc)
-			iov_iter_revert(to, count - iov_iter_count(to));
 		return 0;
 	}
 
 	*err = p9pdu_readf(&req->rc, clnt->proto_version,
 			   "D", &received, &dataptr);
 	if (*err) {
-		if (!non_zc)
-			iov_iter_revert(to, count - iov_iter_count(to));
 		trace_9p_protocol_dump(clnt, &req->rc);
 		p9_req_put(clnt, req);
 		return 0;
@@ -1596,8 +1594,6 @@ p9_client_read_once(struct p9_fid *fid, u64 offset, struct iov_iter *to,
 			p9_req_put(clnt, req);
 			return n;
 		}
-	} else {
-		iov_iter_revert(to, count - received - iov_iter_count(to));
 	}
 	p9_req_put(clnt, req);
 	return received;

On Mon, 21 Oct 2024 21:38:23 +0100, David Howells wrote:
> I think I may have a fix already lurking on my netfs-writeback branch for the
> next merge window.  Can you try the attached?
> 
> David
> 
> 

Applied to the vfs.fixes branch of the vfs/vfs.git tree.
Patches in the vfs.fixes branch should appear in linux-next soon.

Please report any outstanding bugs that were missed during review in a
new review to the original patch series allowing us to drop it.

It's encouraged to provide Acked-bys and Reviewed-bys even though the
patch has now been applied. If possible patch trailers will be updated.

Note that commit hashes shown below are subject to change due to rebase,
trailer updates or similar. If in doubt, please check the listed branch.

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git
branch: vfs.fixes

[1/1] 9p: Don't revert the I/O iterator after reading
      https://git.kernel.org/vfs/vfs/c/09c729da3283

Hi David,

On Mon, Oct 21, 2024 at 21:38:23 +0100, David Howells wrote:
> Hi Antony,
> 
> I think I may have a fix already lurking on my netfs-writeback branch for the
> next merge window.  Can you try the attached?

yes. The fix works. I rebooted a few times and no crash.

Tested-by: Antony Antony <antony.antony@secunet.com>

I am running test script in a loop over night. 

thanks,
-antony

> 
> David
> ---
> Don't revert the I/O iterator before returning from p9_client_read_once().
> netfslib doesn't require the reversion and nor doed 9P directory reading.
> 
> Make p9_client_read() use a temporary iterator to call down into
> p9_client_read_once(), and advance that by the amount read.
> 
> Reported-by: Antony Antony <antony@phenome.org>
> Signed-off-by: David Howells <dhowells@redhat.com>
> cc: Eric Van Hensbergen <ericvh@kernel.org>
> cc: Latchesar Ionkov <lucho@ionkov.net>
> cc: Dominique Martinet <asmadeus@codewreck.org>
> cc: Christian Schoenebeck <linux_oss@crudebyte.com>
> cc: v9fs@lists.linux.dev
> cc: netfs@lists.linux.dev
> cc: linux-fsdevel@vger.kernel.org


> ---
>  net/9p/client.c |   10 +++-------
>  1 file changed, 3 insertions(+), 7 deletions(-)
> 
> diff --git a/net/9p/client.c b/net/9p/client.c
> index 5cd94721d974..be59b0a94eaf 100644
> --- a/net/9p/client.c
> +++ b/net/9p/client.c
> @@ -1519,13 +1519,15 @@ p9_client_read(struct p9_fid *fid, u64 offset, struct iov_iter *to, int *err)
>  	*err = 0;
>  
>  	while (iov_iter_count(to)) {
> +		struct iov_iter tmp = *to;
>  		int count;
>  
> -		count = p9_client_read_once(fid, offset, to, err);
> +		count = p9_client_read_once(fid, offset, &tmp, err);
>  		if (!count || *err)
>  			break;
>  		offset += count;
>  		total += count;
> +		iov_iter_advance(to, count);
>  	}
>  	return total;
>  }
> @@ -1567,16 +1569,12 @@ p9_client_read_once(struct p9_fid *fid, u64 offset, struct iov_iter *to,
>  	}
>  	if (IS_ERR(req)) {
>  		*err = PTR_ERR(req);
> -		if (!non_zc)
> -			iov_iter_revert(to, count - iov_iter_count(to));
>  		return 0;
>  	}
>  
>  	*err = p9pdu_readf(&req->rc, clnt->proto_version,
>  			   "D", &received, &dataptr);
>  	if (*err) {
> -		if (!non_zc)
> -			iov_iter_revert(to, count - iov_iter_count(to));
>  		trace_9p_protocol_dump(clnt, &req->rc);
>  		p9_req_put(clnt, req);
>  		return 0;
> @@ -1596,8 +1594,6 @@ p9_client_read_once(struct p9_fid *fid, u64 offset, struct iov_iter *to,
>  			p9_req_put(clnt, req);
>  			return n;
>  		}
> -	} else {
> -		iov_iter_revert(to, count - received - iov_iter_count(to));
>  	}
>  	p9_req_put(clnt, req);
>  	return received;
>