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Date:   Mon, 23 Mar 2020 15:30:45 +0000
From:   Qais Yousef <qais.yousef@arm.com>
To:     Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org
Cc:     linux-kernel@vger.kernel.org
Subject: Re: lockdep warning in sys_swapon
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On 03/23/20 15:17, Qais Yousef wrote:
> Hi
> 
> I hit the following 2 warnings when running with LOCKDEP=y on arm64 platform
> (juno-r2), running on v5.6-rc6
> 
> The 1st one is when I execute `swapon -a`. The 2nd one happens at boot. I have
> /dev/sda2 as my swap in /etc/fstab
> 
> Note that I either hit 1 OR 2, but didn't hit both warnings at the same time,
> yet at least.
> 
> /dev/sda2 is a usb flash drive, in case it matters somehow.

By the way, I noticed that in claim_swapfile() if we fail we don't release the
lock. Shouldn't we release the lock here?

I tried with that FWIW, but it had no effect on the warnings.


diff --git a/mm/swapfile.c b/mm/swapfile.c
index b2a2e45c9a36..0293e8c7b472 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -2900,8 +2900,10 @@ static int claim_swapfile(struct swap_info_struct *p, struct inode *inode)
        }

        inode_lock(inode);
-       if (IS_SWAPFILE(inode))
+       if (IS_SWAPFILE(inode)) {
+               inode_unlock(inode);
                return -EBUSY;
+       }

        return 0;
 }


Thanks

--
Qais Yousef