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Date:   Fri, 14 Feb 2020 22:15:24 +0100
From:   Domenico Andreoli <domenico.andreoli@linux.com>
To:     "Darrick J. Wong" <darrick.wong@oracle.com>
Cc:     Christoph Hellwig <hch@lst.de>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-pm@vger.kernel.org
Subject: Re: Regression: hibernation is broken since
 e6bc9de714972cac34daa1dc1567ee48a47a9342
Message-ID: <20200214211523.GA32637@dumbo>
Mail-Followup-To: "Darrick J. Wong" <darrick.wong@oracle.com>,
        Christoph Hellwig <hch@lst.de>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-pm@vger.kernel.org
References: <20200213172351.GA6747@dumbo>
 <20200213175753.GS6874@magnolia>
 <20200213183515.GA8798@dumbo>
 <20200213193410.GB6868@magnolia>
 <20200213194135.GF6870@magnolia>
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[ added linux-pm ]

On Thu, Feb 13, 2020 at 11:41:35AM -0800, Darrick J. Wong wrote:
> On Thu, Feb 13, 2020 at 11:34:10AM -0800, Darrick J. Wong wrote:
> > 
> > Well ... you could try the in-kernel hibernate (which I think is what
> > 'systemctl hibernate' does), though you'd lose the nifty features of
> > ?swsusp.

Indeed 'systemctl hibernate' works perfectly with v5.6-rc1 in my setup.

> > In the end, though, I'll probably have to revert all those IS_SWAPFILE
> > checks (at least if CONFIG_HIBERNATION=y) since it's not fair to force
> > you to totally reconfigure your hibernation setup.
> 
> Also, does the following partial revert fix uswsusp for you?  It'll
> allow the direct writes that uswsusp wants to do, while leaving the rest
> (mmap writes) in place.
> 
> --D
> 
> diff --git a/fs/block_dev.c b/fs/block_dev.c
> index 69bf2fb6f7cd..077d9fa6b87d 100644
> --- a/fs/block_dev.c
> +++ b/fs/block_dev.c
> @@ -2001,8 +2001,10 @@ ssize_t blkdev_write_iter(struct kiocb *iocb, struct iov_iter *from)
>  	if (bdev_read_only(I_BDEV(bd_inode)))
>  		return -EPERM;
>  
> +#ifndef CONFIG_HIBERNATION
>  	if (IS_SWAPFILE(bd_inode))
>  		return -ETXTBSY;
> +#endif

This alone is enough to make uswsusp work again.

I propose this alternative:

--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -2001,7 +2001,8 @@ ssize_t blkdev_write_iter(struct kiocb *iocb, struct iov_iter *from)
        if (bdev_read_only(I_BDEV(bd_inode)))
                return -EPERM;
 
-       if (IS_SWAPFILE(bd_inode))
+       /* Hibernation might happen via uswsusp, let it write to the swap */
+       if (IS_SWAPFILE(bd_inode) && !IS_ENABLED(CONFIG_HIBERNATION))
                return -ETXTBSY;
 
        if (!iov_iter_count(from))

I looked for a more selective way to enable writes to swap at runtime,
so I tried with system_entering_hibernation() but it's not yet armed
at the point in which uswsusp wants to write to the swap and therefore
it does not work.

--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -34,6 +34,7 @@
 #include <linux/task_io_accounting_ops.h>
 #include <linux/falloc.h>
 #include <linux/uaccess.h>
+#include <linux/suspend.h>
 #include "internal.h"

 struct bdev_inode {
@@ -2001,7 +2002,8 @@ ssize_t blkdev_write_iter(struct kiocb *iocb, struct iov_iter *from)
        if (bdev_read_only(I_BDEV(bd_inode)))
                return -EPERM;

-       if (IS_SWAPFILE(bd_inode))
+       /* Hibernation might happen via uswsusp, let it write to the swap */
+       if (IS_SWAPFILE(bd_inode) && !system_entering_hibernation())
                return -ETXTBSY;

        if (!iov_iter_count(from))

>  	if (!iov_iter_count(from))
>  		return 0;
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 1784478270e1..3df3211abe25 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -2920,8 +2920,10 @@ inline ssize_t generic_write_checks(struct kiocb *iocb, struct iov_iter *from)
>  	loff_t count;
>  	int ret;
>  
> +#ifndef CONFIG_HIBERNATION
>  	if (IS_SWAPFILE(inode))
>  		return -ETXTBSY;
> +#endif
>  
>  	if (!iov_iter_count(from))
>  		return 0;

The above is not needed in my case but I'm not sure it would not be
needed in some other configuration of uswsusp.

Dom

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