linux-kernel - Re: [syzbot] [io-uring?] WARNING in __io_uring

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Message-ID: <Z0kDWtjmlI_LwP5S@casper.infradead.org>
Date: Thu, 28 Nov 2024 23:57:14 +0000
From: Matthew Wilcox <willy@...radead.org>
To: Jann Horn <jannh@...gle.com>
Cc: syzbot <syzbot+cc36d44ec9f368e443d3@...kaller.appspotmail.com>,
	asml.silence@...il.com, axboe@...nel.dk, io-uring@...r.kernel.org,
	linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [syzbot] [io-uring?] WARNING in __io_uring_free

On Fri, Nov 29, 2024 at 12:30:35AM +0100, Jann Horn wrote:
> > ------------[ cut here ]------------
> > WARNING: CPU: 0 PID: 16 at io_uring/tctx.c:51 __io_uring_free+0xfa/0x140 io_uring/tctx.c:51
> 
> This warning is a check for WARN_ON_ONCE(!xa_empty(&tctx->xa)); and as
> Jens pointed out, this was triggered after error injection caused a
> memory allocation inside xa_store() to fail.
> 
> Is there maybe an issue where xa_store() can fail midway through while
> allocating memory for the xarray, so that xa_empty() is no longer true
> even though there is nothing in the xarray? (And if yes, is that
> working as intended?)

Yes, that's a known possibility.  We have similar problems when people
use error injection with mapping->i_pages.  The effort to fix it seems
disproportionate to the severity of the problem.