Documentation/mm: add details about kmap_local_page() and preemption
What happens if a thread is preempted after mapping pages with kmap_local_page() was questioned recently.[1] Commit f3ba3c71 ("mm/highmem: Provide kmap_local*") from Thomas Gleixner explains clearly that on context switch, the maps of an outgoing task are removed and the map of the incoming task are restored and that kmap_local_page() can be invoked from both preemptible and atomic contexts.[2] Therefore, for the purpose to make it clearer that users can call kmap_local_page() from contexts that allow preemption, rework a couple of sentences and add further information in highmem.rst. [1] https://lore.kernel.org/lkml/5303077.Sb9uPGUboI@opensuse/ [2] https://lore.kernel.org/all/20201118204007.468533059@linutronix.de/ Link: https://lkml.kernel.org/r/20220728154844.10874-8-fmdefrancesco@gmail.comSigned-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com> Suggested-by: Ira Weiny <ira.weiny@intel.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Mike Rapoport <rppt@linux.ibm.com> Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Peter Collingbourne <pcc@google.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Will Deacon <will@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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