Linux 5.10 compat: restore custom uio_prefaultpages() #11493
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As part of commit 1c2358c the custom uio_prefaultpages() code was removed in favor of using the generic kernel provided iov_iter_fault_in_readable() interface. Unfortunately, it turns out that up until the Linux 4.7 kernel the function would only ever fault in the first iovec of the iov_iter. The result being uiomove_iov() may hang waiting for the page. This commit effectively restores the custom uio_prefaultpages() pages code for Linux 4.9 and earlier kernels which contain the troublesome version of iov_iter_fault_in_readable(). Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov> Closes openzfs#11463 Closes openzfs#11484
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Motivation and Context
Backport of PR #11484 for the 2.0.2 release.
Description
As part of commit 1c2358c the custom uio_prefaultpages() code
was removed in favor of using the generic kernel provided
iov_iter_fault_in_readable() interface. Unfortunately, it
turns out that up until the Linux 4.7 kernel the function would
only ever fault in the first iovec of the iov_iter. The result
being uiomove_iov() may hang waiting for the page.
This commit effectively restores the custom uio_prefaultpages()
pages code for Linux 4.9 and earlier kernels which contain the
troublesome version of iov_iter_fault_in_readable().
How Has This Been Tested?
See #11484
Types of changes