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08e9cbe75f
This code was using get_user_pages*(), in a "Case 1" scenario (Direct IO),
using the categorization from [1]. That means that it's time to convert the
get_user_pages*() + put_page() calls to pin_user_pages*() +
unpin_user_pages() calls.
There is some helpful background in [2]: basically, this is a small part of
fixing a long-standing disconnect between pinning pages, and file systems'
use of those pages.
Note that this effectively changes the code's behavior as well: it now
ultimately calls set_page_dirty_lock(), instead of SetPageDirty().This is
probably more accurate.
As Christoph Hellwig put it, "set_page_dirty() is only safe if we are
dealing with a file backed page where we have reference on the inode it
hangs off." [3]
Also, this deletes one of the two FIXME comments (about refcounting),
because there is nothing wrong with the refcounting at this point.
[1] Documentation/core-api/pin_user_pages.rst
[2] "Explicit pinning of user-space pages":
https://lwn.net/Articles/807108/
[3] https://lore.kernel.org/r/20190723153640.GB720@lst.de
Link: https://lore.kernel.org/r/20200526182709.99599-1-jhubbard@nvidia.com
Cc: "Kai Mäkisara (Kolumbus)" <kai.makisara@kolumbus.fi>
Cc: Bart Van Assche <bvanassche@acm.org>
Cc: James E.J. Bottomley <jejb@linux.ibm.com>
Cc: Martin K. Petersen <martin.petersen@oracle.com>
Cc: linux-scsi@vger.kernel.org
Acked-by: Kai Mäkisara <kai.makisara@kolumbus.fi>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.