linux-kernel - Re: autofs: add autofs_parse

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Message-Id: <f1cddf6e-2103-4786-84ff-12c305341d7c@app.fastmail.com>
Date:   Fri, 20 Oct 2023 13:23:22 +0200
From:   "Arnd Bergmann" <arnd@...db.de>
To:     "Dan Carpenter" <dan.carpenter@...aro.org>,
        "Anders Roxell" <anders.roxell@...aro.org>
Cc:     "Naresh Kamboju" <naresh.kamboju@...aro.org>,
        "open list" <linux-kernel@...r.kernel.org>,
        lkft-triage@...ts.linaro.org, linux-fsdevel@...r.kernel.org,
        autofs@...r.kernel.org, "Ian Kent" <raven@...maw.net>,
        "Bill O'Donnell" <bodonnel@...hat.com>,
        "Christian Brauner" <brauner@...nel.org>
Subject: Re: autofs: add autofs_parse_fd()

On Fri, Oct 20, 2023, at 12:45, Dan Carpenter wrote:
> On Fri, Oct 20, 2023 at 11:55:57AM +0200, Anders Roxell wrote:
>> On Fri, 20 Oct 2023 at 08:37, Arnd Bergmann <arnd@...db.de> wrote:
>> >
>> > On Thu, Oct 19, 2023, at 17:27, Naresh Kamboju wrote:
>> > > The qemu-x86_64 and x86_64 booting with 64bit kernel and 32bit rootfs we call
>> > > it as compat mode boot testing. Recently it started to failed to get login
>> > > prompt.
>> > >
>> > > We have not seen any kernel crash logs.
>> > >
>> > > Anders, bisection is pointing to first bad commit,
>> > > 546694b8f658 autofs: add autofs_parse_fd()
>> > >
>> > > Reported-by: Linux Kernel Functional Testing <lkft@...aro.org>
>> > > Reported-by: Anders Roxell <anders.roxell@...aro.org>
>> >
>> > I tried to find something in that commit that would be different
>> > in compat mode, but don't see anything at all -- this appears
>> > to be just a simple refactoring of the code, unlike the commits
>> > that immediately follow it and that do change the mount
>> > interface.
>> >
>> > Unfortunately this makes it impossible to just revert the commit
>> > on top of linux-next. Can you double-check your bisection by
>> > testing 546694b8f658 and the commit before it again?
>> 
>> I tried these two patches again:
>> 546694b8f658 ("autofs: add autofs_parse_fd()") - doesn't boot
>> bc69fdde0ae1 ("autofs: refactor autofs_prepare_pipe()") - boots
>> 
>
> One difference that I notice between those two patches is that we no
> long call autofs_prepare_pipe().  We just call autofs_check_pipe().

Indeed, so some of the f_flags end up being different. I assumed
this was done intentionally, but it might be worth checking if
the patch below makes any difference when the flags get put
back the way they were. This is probably not the correct fix, but
may help figure out what is going on. It should apply to anything
from 546694b8f658 ("autofs: add autofs_parse_fd()") to the current
linux-next:

--- a/fs/autofs/inode.c
+++ b/fs/autofs/inode.c
@@ -358,6 +358,11 @@ static int autofs_fill_super(struct super_block *s, struct fs_context *fc)
        pr_debug("pipe fd = %d, pgrp = %u\n",
                 sbi->pipefd, pid_nr(sbi->oz_pgrp));
 
+        /* We want a packet pipe */
+        sbi->pipe->f_flags |= O_DIRECT;
+        /* We don't expect -EAGAIN */
+        sbi->pipe->f_flags &= ~O_NONBLOCK;
+
        sbi->flags &= ~AUTOFS_SBI_CATATONIC;
 
        /*