A question on the function clean_bdev_bh_alias

[valdis.kletnieks at vt.edu]

On Fri, 10 Aug 2018 22:48:43 +0800, "Larry" said:

> Does it intend to remove existent pages in block device's page cache
> if some new page cache of a vfs file was created whose block number
> range has overlaps with its block device page cache?

That's a situation you *really* hope doesn't arise.

Consider if you have (for example) an ext4 filesystem on /dev/sda4 mounted on
/foobar.

For there to be page cache for the ext4 filesystem and also page cache for
the block device, that means that something is writing to a file on /foobar
while something else is writing directly to /dev/sda4.

That's a really good way to corrupt the filesystem (and is why it's a Really
Bad Idea to fsck a mounted filesystem).  And no, merely trimming cache
pages that overlap doesn't even come *close* to fixing the problem...

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