set_page_dirty vs set_page_dirty_lock

From: Michael S. Tsirkin
Date: Thu Dec 08 2005 - 13:47:15 EST


Hi!
The comment at set_page_dirty_lock says:

/*
* set_page_dirty() is racy if the caller has no reference against
* page->mapping->host, and if the page is unlocked. This is because another
* CPU could truncate the page off the mapping and then free the mapping.
*
* Usually, the page _is_ locked, or the caller is a user-space process which
* holds a reference on the inode by having an open file.
*
* In other cases, the page should be locked before running set_page_dirty().
*/

Still, I wander whether it might be OK to use set_page_dirty
in another case - if I previously got a reference to the page
with get_user_pages?
The page wouldnt be written back in this case, would it?
What if I'm in the middle of a system call?

Thanks,

--
MST
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