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Date: Thu, 26 Mar 2026 07:08:40 +0100
From: Christoph Hellwig <hch@lst.de>
To: Dave Chinner <dgc@kernel.org>
Cc: Hans Holmberg <hans.holmberg@wdc.com>, Carlos Maiolino <cem@kernel.org>,
	Dave Chinner <david@fromorbit.com>,
	"Darrick J . Wong" <djwong@kernel.org>,
	Christoph Hellwig <hch@lst.de>, Damien Le Moal <dlemoal@kernel.org>,
	linux-xfs@vger.kernel.org, stable@vger.kernel.org
Subject: Re: [PATCH v2] xfs: start gc on zonegc_low_space attribute updates
Message-ID: <20260326060840.GA23733@lst.de>
References: <20260325124312.26349-1-hans.holmberg@wdc.com> <acSfSmE_IBjWl_cR@dread>
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User-Agent: Mutt/1.5.17 (2007-11-01)

On Thu, Mar 26, 2026 at 01:51:54PM +1100, Dave Chinner wrote:
> > - Added a new helper to wake up the gc thread in stead of unparking it,
> >   which is required to make this work properly.
> > - Added protection against races with unmounts as sysfs gets torn down
> >   after the zone info struct is freed. This also avoids unneded
> >   wakeups during remount.
> 
> Isn't that a deadlock vector?
> 
> i.e. unmount takes s_umount, concurrently userspace writes a new
> value to sysfs file. sysfs file write blocks on s_umount, unmount
> blocks holding s_umount waiting for sysfs file reference count to go
> to zero to destroy it?

Given that the code does a trylock it should not.