From: Miklos Szeredi <miklos@szeredi.hu>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>,
Oleg Nesterov <oleg@redhat.com>,
Tycho Andersen <tycho@tycho.pizza>,
"Serge E. Hallyn" <serge@hallyn.com>,
linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: Re: [RFC][PATCH v2] fuse: In fuse_flush only wait if someone wants the return code
Date: Tue, 2 Aug 2022 14:50:32 +0200 [thread overview]
Message-ID: <CAJfpegsTmiO-sKaBLgoVT4WxDXBkRES=HF1YmQN1ES7gfJEJ+w@mail.gmail.com> (raw)
In-Reply-To: <875yjfdw3a.fsf_-_@email.froward.int.ebiederm.org>
On Sat, 30 Jul 2022 at 07:11, Eric W. Biederman <ebiederm@xmission.com> wrote:
>
>
> In my very light testing this resolves a hang where a thread of the
> fuse server was accessing the fuse filesystem (the fuse server is
> serving up), when the fuse server is killed.
>
> The practical problem is that the fuse server file descriptor was
> being closed after the file descriptor into the fuse filesystem so
> that the fuse filesystem operations were being blocked for instead of
> being aborted. Simply skipping the unnecessary wait resolves this
> issue.
>
> This is just a proof of concept and someone should look to see if the
> fuse max_background limit could cause a problem with this approach.
max_background just throttles the number of background requests that
the userspace filesystem can *unqueue*. It doesn't affect queuing in
any way.
> Additionally testing PF_EXITING is a very crude way to tell if someone
> wants the return code from the vfs flush operation. As such in the
> long run it probably makes sense to get some direct vfs support for
> knowing if flush needs to block until all of the flushing is complete
> and a status/return code can be returned.
>
> Unless I have missed something this is a generic optimization that can
> apply to many network filesystems.
>
> Al, vfs folks? (igrab/iput sorted so as not to be distractions).
>
> Perhaps a .flush_async method without a return code and a
> filp_close_async function without a return code to take advantage of
> this in the general sense.
>
> Waiting potentially indefinitely for user space in do_exit seems like a
> bad idea. Especially when all that the wait is for is to get a return
> code that will never be examined.
The wait is for posix locks to get unlocked. But "remote" posix locks
are almost never used due to problems like this, so I think it's safe
to do this.
>
> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
> ---
> fs/fuse/file.c | 59 ++++++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 59 insertions(+)
>
> diff --git a/fs/fuse/file.c b/fs/fuse/file.c
> index 05caa2b9272e..2bd94acd761f 100644
> --- a/fs/fuse/file.c
> +++ b/fs/fuse/file.c
> @@ -464,6 +464,62 @@ static void fuse_sync_writes(struct inode *inode)
> fuse_release_nowrite(inode);
> }
>
> +struct fuse_flush_args {
> + struct fuse_args args;
> + struct fuse_flush_in inarg;
> + struct inode *inode;
> +};
> +
> +static void fuse_flush_end(struct fuse_mount *fm, struct fuse_args *args, int err)
> +{
> + struct fuse_flush_args *fa = container_of(args, typeof(*fa), args);
> +
> + if (err == -ENOSYS) {
> + fm->fc->no_flush = 1;
> + err = 0;
> + }
> +
> + /*
> + * In memory i_blocks is not maintained by fuse, if writeback cache is
> + * enabled, i_blocks from cached attr may not be accurate.
> + */
> + if (!err && fm->fc->writeback_cache)
> + fuse_invalidate_attr_mask(fa->inode, STATX_BLOCKS);
> +
> + iput(fa->inode);
Filesystems might expect not just he inode to not be destroyed but
also the file, so do what other file operations do, keep a ref on ff:
fuse_file_put(fa->ff, false, false);
> + kfree(fa);
> +}
> +
> +static int fuse_flush_async(struct file *file, fl_owner_t id)
> +{
> + struct inode *inode = file_inode(file);
> + struct fuse_mount *fm = get_fuse_mount(inode);
> + struct fuse_file *ff = file->private_data;
> + struct fuse_flush_args *fa;
> + int err;
> +
> + fa = kzalloc(sizeof(*fa), GFP_KERNEL);
> + if (!fa)
> + return -ENOMEM;
> +
> + fa->inarg.fh = ff->fh;
> + fa->inarg.lock_owner = fuse_lock_owner_id(fm->fc, id);
> + fa->args.opcode = FUSE_FLUSH;
> + fa->args.nodeid = get_node_id(inode);
> + fa->args.in_numargs = 1;
> + fa->args.in_args[0].size = sizeof(fa->inarg);
> + fa->args.in_args[0].value = &fa->inarg;
> + fa->args.force = true;
> + fa->args.end = fuse_flush_end;
> + fa->inode = igrab(inode);
fa->ff = fuse_file_get(ff);
> +
> + err = fuse_simple_background(fm, &fa->args, GFP_KERNEL);
> + if (err)
> + fuse_flush_end(fm, &fa->args, err);
> +
> + return err;
> +}
> +
> static int fuse_flush(struct file *file, fl_owner_t id)
> {
> struct inode *inode = file_inode(file);
> @@ -495,6 +551,9 @@ static int fuse_flush(struct file *file, fl_owner_t id)
> if (fm->fc->no_flush)
> goto inval_attr_out;
>
> + if (current->flags & PF_EXITING)
> + return fuse_flush_async(file, id);
> +
> memset(&inarg, 0, sizeof(inarg));
> inarg.fh = ff->fh;
> inarg.lock_owner = fuse_lock_owner_id(fm->fc, id);
> --
> 2.35.3
>
next prev parent reply other threads:[~2022-08-02 12:51 UTC|newest]
Thread overview: 61+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-23 17:21 strange interaction between fuse + pidns Tycho Andersen
2022-06-23 21:55 ` Vivek Goyal
2022-06-23 23:41 ` Tycho Andersen
2022-06-24 17:36 ` Vivek Goyal
2022-07-11 10:35 ` Miklos Szeredi
2022-07-11 13:59 ` Miklos Szeredi
2022-07-11 20:25 ` Tycho Andersen
2022-07-11 21:37 ` Eric W. Biederman
2022-07-11 22:53 ` Tycho Andersen
2022-07-11 23:06 ` Eric W. Biederman
2022-07-12 13:43 ` Tycho Andersen
2022-07-12 14:34 ` Eric W. Biederman
2022-07-12 15:14 ` Tycho Andersen
2022-07-13 17:53 ` [PATCH] sched: __fatal_signal_pending() should also check PF_EXITING Tycho Andersen
2022-07-20 15:03 ` Serge E. Hallyn
2022-07-20 20:58 ` Tycho Andersen
2022-07-21 1:54 ` Serge E. Hallyn
2022-07-27 15:44 ` Tycho Andersen
2022-07-27 16:32 ` Eric W. Biederman
2022-07-27 17:55 ` Tycho Andersen
2022-07-28 18:48 ` Eric W. Biederman
2022-07-27 17:55 ` Oleg Nesterov
2022-07-27 18:18 ` Tycho Andersen
2022-07-27 19:19 ` Oleg Nesterov
2022-07-27 19:40 ` Tycho Andersen
2022-07-28 9:12 ` Oleg Nesterov
2022-07-28 21:20 ` Tycho Andersen
2022-07-29 5:04 ` Eric W. Biederman
2022-07-29 13:50 ` Tycho Andersen
2022-07-29 16:15 ` Eric W. Biederman
2022-07-29 16:48 ` Tycho Andersen
2022-07-29 17:40 ` [RFC][PATCH] fuse: In fuse_flush only wait if someone wants the return code Eric W. Biederman
2022-07-29 20:47 ` Oleg Nesterov
2022-07-30 0:15 ` Al Viro
2022-07-30 5:10 ` [RFC][PATCH v2] " Eric W. Biederman
2022-08-01 15:16 ` Tycho Andersen
2022-08-02 12:50 ` Miklos Szeredi [this message]
2022-08-15 13:59 ` Tycho Andersen
2022-08-15 17:55 ` Serge E. Hallyn
2022-09-01 14:06 ` [PATCH] " Tycho Andersen
2022-09-19 15:03 ` Tycho Andersen
2022-09-20 18:02 ` Serge E. Hallyn
2022-09-26 14:17 ` Tycho Andersen
2022-09-27 9:46 ` Miklos Szeredi
2022-09-29 14:05 ` [fuse-devel] " Stef Bon
2022-09-29 16:39 ` [PATCH v2] " Tycho Andersen
2022-09-30 13:35 ` Miklos Szeredi
2022-09-30 14:01 ` Tycho Andersen
2022-09-30 14:41 ` Miklos Szeredi
2022-09-30 16:09 ` Tycho Andersen
2022-10-26 9:01 ` Miklos Szeredi
2022-11-14 16:02 ` [PATCH v3] " Tycho Andersen
2022-11-28 15:00 ` Tycho Andersen
2022-12-08 14:26 ` Miklos Szeredi
2022-12-08 17:49 ` Tycho Andersen
2022-12-19 19:16 ` Tycho Andersen
2023-01-03 14:51 ` Tycho Andersen
2023-01-05 15:15 ` Serge E. Hallyn
2023-01-26 14:12 ` Miklos Szeredi
2022-09-30 19:47 ` [PATCH] " Serge E. Hallyn
2022-09-19 15:46 ` [RFC][PATCH v2] " Eric W. Biederman
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