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Message-ID: <ZfzQz5hwECOEGYVL@google.com>
Date: Thu, 21 Mar 2024 17:29:03 -0700
From: Jaegeuk Kim <jaegeuk@...nel.org>
To: Hillf Danton <hdanton@...a.com>
Cc: linux-kernel@...r.kernel.org,
Light Hsieh (謝明燈) <Light.Hsieh@...iatek.com>,
linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [PATCH] f2fs: avoid the deadlock case when stopping discard
thread
On 03/22, Hillf Danton wrote:
> On Tue, 19 Mar 2024 17:14:42 -0700 Jaegeuk Kim <jaegeuk@...nel.org>
> > f2fs_ioc_shutdown(F2FS_GOING_DOWN_NOSYNC) issue_discard_thread
> > - mnt_want_write_file()
> > - sb_start_write(SB_FREEZE_WRITE)
> __sb_start_write()
> percpu_down_read()
> > - sb_start_intwrite(SB_FREEZE_FS);
> __sb_start_write()
> percpu_down_read()
>
> Given lock acquirers for read on both sides, wtf deadlock are you fixing?
Damn. I couldn't think _write uses _read sem.
>
> > - f2fs_stop_checkpoint(sbi, false, : waiting
> > STOP_CP_REASON_SHUTDOWN);
> > - f2fs_stop_discard_thread(sbi);
> > - kthread_stop()
> > : waiting
> >
> > - mnt_drop_write_file(filp);
>
> More important, feel free to add in spin.
I posted this patch before Light reported.
And, in the report, I didn't get this:
f2fs_ioc_shutdown() --> freeze_bdev() --> freeze_super() --> sb_wait_write(sb, SB_FREEZE_FS) --> ... ->percpu_down_write().
because f2fs_ioc_shutdown() calls f2fs_stop_discard_thread() after thaw_bdev()
like this order.
-> freeze_bdev()
-> thaw_bdev()
-> f2fs_stop_discard_thread()
Am I missing something?
>
> Reported-by: "Light Hsieh (謝明燈)" <Light.Hsieh@...iatek.com>
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