linux-kernel - Re: [LTP] [linus:master] [iomap] 219580eea1: ltp.writev07.fail

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Date:   Thu, 13 Jul 2023 17:34:55 +0200
From:   Cyril Hrubis <chrubis@...e.cz>
To:     Christoph Hellwig <hch@....de>
Cc:     kernel test robot <oliver.sang@...el.com>,
        "Darrick J. Wong" <djwong@...nel.org>,
        Andreas Gruenbacher <agruenba@...hat.com>,
        Miklos Szeredi <miklos@...redi.hu>,
        Matthew Wilcox <willy@...radead.org>, cluster-devel@...hat.com,
        Ilya Dryomov <idryomov@...il.com>,
        Miklos Szeredi <mszeredi@...hat.com>,
        Chao Yu <chao@...nel.org>, linux-fsdevel@...r.kernel.org,
        Al Viro <viro@...iv.linux.org.uk>,
        Jaegeuk Kim <jaegeuk@...nel.org>, Xiubo Li <xiubli@...hat.com>,
        Trond Myklebust <trond.myklebust@...merspace.com>,
        ltp@...ts.linux.it, lkp@...el.com, Jens Axboe <axboe@...nel.dk>,
        Christian Brauner <brauner@...nel.org>,
        Theodore Ts'o <tytso@....edu>,
        Johannes Thumshirn <johannes.thumshirn@....com>,
        linux-kernel@...r.kernel.org, linux-xfs@...r.kernel.org,
        Anna Schumaker <anna@...nel.org>, oe-lkp@...ts.linux.dev,
        Andrew Morton <akpm@...ux-foundation.org>,
        Hannes Reinecke <hare@...e.de>
Subject: Re: [LTP] [linus:master] [iomap]  219580eea1: ltp.writev07.fail

Hi!
> I can't reproduce this on current mainline.  Is this a robust failure
> or flapping test?  Especiall as the FAIL conditions look rather
> unrelated.

Actually the test is spot on, the difference is that previously the
error was returned form the iomap_file_buffered_write() only if we
failed with the first buffer from the iov, now we always return the
error and we do not advance the offset.

The change that broke it:

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index 063133ec77f4..550525a525c4 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -864,16 +864,19 @@ iomap_file_buffered_write(struct kiocb *iocb, struct iov_iter *i,
                .len            = iov_iter_count(i),
                .flags          = IOMAP_WRITE,
        };
-       int ret;
+       ssize_t ret;

        if (iocb->ki_flags & IOCB_NOWAIT)
                iter.flags |= IOMAP_NOWAIT;

        while ((ret = iomap_iter(&iter, ops)) > 0)
                iter.processed = iomap_write_iter(&iter, i);
-       if (iter.pos == iocb->ki_pos)
+
+       if (unlikely(ret < 0))
                return ret;
-       return iter.pos - iocb->ki_pos;
+       ret = iter.pos - iocb->ki_pos;
+       iocb->ki_pos += ret;
+       return ret;
 }

I suppose that we shoudl fix is with something as:

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index adb92cdb24b0..bfb39f7bc303 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -872,11 +872,12 @@ iomap_file_buffered_write(struct kiocb *iocb, struct iov_iter *i,
        while ((ret = iomap_iter(&iter, ops)) > 0)
                iter.processed = iomap_write_iter(&iter, i);

+       iocb->ki_pos += iter.pos - iocb->ki_pos;
+
        if (unlikely(ret < 0))
                return ret;
-       ret = iter.pos - iocb->ki_pos;
-       iocb->ki_pos += ret;
-       return ret;
+
+       return iter.pos - iocb->ki_pos;
 }
 EXPORT_SYMBOL_GPL(iomap_file_buffered_write);


-- 
Cyril Hrubis
chrubis@...e.cz