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Date:   Wed, 30 Mar 2022 08:51:21 +0900
From:   Dominique Martinet <>
To:     Tetsuo Handa <>
Cc:     Andrew Perepechko <>,
        Andreas Dilger <>,
        Theodore Ts'o <>,
        syzbot <>,,,,
        "open list:EXT4 FILE SYSTEM" <>
Subject: Re: [syzbot] possible deadlock in p9_write_work

Tetsuo Handa wrote on Wed, Mar 30, 2022 at 07:35:47AM +0900:
> This seems to be an example of
> introduced by "ext4: truncate during setxattr leads to kernel panic".

Thanks for the pointer

> Please don't use schedule_work() if you need to use flush_scheduled_work().

In this case we don't call flush_scheduled_work -- ext4 does.
The problem is mixing in the two subsystems when someone (e.g. syzbot)
opens an ext4 file and passes that fd to 9p when mounting with e.g.
mount -t 9p -o rfdno=<no>,wfdno=<no>

Frankly that's just not something I consider useful, interacting through
9p to a local file doesn't make sense except for testing.

If that is a real problem, the simplest way out would be to just forbid
non-socket FDs if it's something we can check.

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