From: Jan Kara <jack@suse.cz>
To: Andreas Gruenbacher <agruenba@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Alexander Viro <viro@zeniv.linux.org.uk>,
Christoph Hellwig <hch@infradead.org>,
"Darrick J. Wong" <djwong@kernel.org>, Jan Kara <jack@suse.cz>,
Matthew Wilcox <willy@infradead.org>,
cluster-devel@redhat.com, linux-fsdevel@vger.kernel.org,
linux-kernel@vger.kernel.org, ocfs2-devel@oss.oracle.com
Subject: Re: [PATCH v3 7/7] gfs2: Fix mmap + page fault deadlocks for direct I/O
Date: Mon, 26 Jul 2021 19:02:50 +0200 [thread overview]
Message-ID: <20210726170250.GL20621@quack2.suse.cz> (raw)
In-Reply-To: <20210723205840.299280-8-agruenba@redhat.com>
On Fri 23-07-21 22:58:40, Andreas Gruenbacher wrote:
> Also disable page faults during direct I/O requests and implement the same kind
> of retry logic as in the buffered I/O case.
>
> Direct I/O requests differ from buffered I/O requests in that they use
> bio_iov_iter_get_pages for grabbing page references and faulting in pages
> instead of triggering real page faults. Those manual page faults can be
> disabled with the iocb->noio flag.
>
> Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
> ---
> fs/gfs2/file.c | 34 +++++++++++++++++++++++++++++++++-
> 1 file changed, 33 insertions(+), 1 deletion(-)
>
> diff --git a/fs/gfs2/file.c b/fs/gfs2/file.c
> index f66ac7f56f6d..7986f3be69d2 100644
> --- a/fs/gfs2/file.c
> +++ b/fs/gfs2/file.c
> @@ -782,21 +782,41 @@ static ssize_t gfs2_file_direct_read(struct kiocb *iocb, struct iov_iter *to,
> struct file *file = iocb->ki_filp;
> struct gfs2_inode *ip = GFS2_I(file->f_mapping->host);
> size_t count = iov_iter_count(to);
> + size_t written = 0;
> ssize_t ret;
>
> + /*
> + * In this function, we disable page faults when we're holding the
> + * inode glock while doing I/O. If a page fault occurs, we drop the
> + * inode glock, fault in the pages manually, and then we retry. Other
> + * than in gfs2_file_read_iter, iomap_dio_rw can trigger implicit as
> + * well as manual page faults, and we need to disable both kinds
> + * separately.
> + */
> +
> if (!count)
> return 0; /* skip atime */
>
> gfs2_holder_init(ip->i_gl, LM_ST_DEFERRED, 0, gh);
> +retry:
> ret = gfs2_glock_nq(gh);
> if (ret)
> goto out_uninit;
>
> + pagefault_disable();
Is there any use in pagefault_disable() here? iomap_dio_rw() should not
trigger any page faults anyway, should it?
Honza
--
Jan Kara <jack@suse.com>
SUSE Labs, CR
next prev parent reply other threads:[~2021-07-26 17:09 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-23 20:58 [PATCH v3 0/7] gfs2: Fix mmap + page fault deadlocks Andreas Gruenbacher
2021-07-23 20:58 ` [PATCH v3 1/7] iov_iter: Introduce fault_in_iov_iter helper Andreas Gruenbacher
2021-07-23 23:40 ` Linus Torvalds
2021-07-24 7:51 ` Andreas Grünbacher
2021-07-24 1:52 ` Al Viro
2021-07-24 8:05 ` Andreas Grünbacher
2021-07-26 16:33 ` Jan Kara
2021-07-26 17:15 ` Linus Torvalds
2021-07-23 20:58 ` [PATCH v3 2/7] gfs2: Add wrapper for iomap_file_buffered_write Andreas Gruenbacher
2021-07-23 20:58 ` [PATCH v3 3/7] gfs2: Fix mmap + page fault deadlocks for buffered I/O Andreas Gruenbacher
2021-07-23 20:58 ` [PATCH v3 4/7] iomap: Fix iomap_dio_rw return value for user copies Andreas Gruenbacher
2021-07-23 20:58 ` [PATCH v3 5/7] iomap: Support restarting direct I/O requests after user copy failures Andreas Gruenbacher
2021-07-26 17:19 ` Jan Kara
[not found] ` <CAHpGcMLtQ1=WOT1mTUS4=iWBwHLQ-EBzY=+XuSGJfu4gVPYTLw@mail.gmail.com>
2021-07-26 18:08 ` Jan Kara
2021-07-23 20:58 ` [PATCH v3 6/7] iov_iter: Introduce noio flag to disable page faults Andreas Gruenbacher
2021-07-23 20:58 ` [PATCH v3 7/7] gfs2: Fix mmap + page fault deadlocks for direct I/O Andreas Gruenbacher
2021-07-26 17:02 ` Jan Kara [this message]
[not found] ` <CAHpGcMLOZhZ7tGrY7rcYWUwx12sY884T=eC-Ckna63PBmF=zwA@mail.gmail.com>
2021-07-26 18:00 ` Jan Kara
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