** Description changed:
- Ensure zero's are written to backing store of at least one page size and
- sync it so that we can be 100% sure that mmap'ing the page into memory
- is backed with data so we don't get BUS errors on some platforms such as
- armhf Raspi2.
+ == SRU Justification BIONIC, DISCO ==
+
+ When running the mcontend stressor on slow armhf devices that have slow
+ memory backed I/O one can get SIGBUS on a file backed mmap because the
+ flush has been slow to allocate the page and we're mmapping and
+ accessing a as yet allocated page on the backing store.
+
+ == Test Proceedure ==
+
+ Run:
+
+
+ stress-ng --mcontend 1 -t 10 -v
+
+ without the fix, we get SIGBUS failures because we touch a page that has
+ not yet had the backing mmap page allocated and flushed to the file
+ system.
+
+ == Fix ==
+
+ commit c3678dadee23f9b8783038f54463cff5741a9cbe
+ Author: Colin Ian King <colin.k...@canonical.com>
+ Date: Mon Sep 23 15:54:13 2019 +0100
+
+ stress-mcontend: ensure mmap'd file is sync'd with zero data (LP:
#1845011)
+
+ Write zero's to backing store of at least one page size and sync
+ it so that we can be 100% sure that mmap'ing the page into memory
+ is backed with data so we don't get BUS errors on some platforms
+ such as armhf Raspi2.
+
+ Also fix broken sanity check on 2nd mmap out of memory failure.
+
+ Signed-off-by: Colin Ian King <colin.k...@canonical.com>
+
+
+ == Regression Potential ==
+
+ Minimal. This replaces the more esoteric fallocate() with a direct set
+ of file writes and a sync to ensure data is written back before we mmap
+ onto it. The fixed behaviour is slower as we introduce a sync, so we
+ have the possibility of the sync blocking for a long time if the system
+ has a lot of dirty data, but this is necessary as fsync() is less
+ portable and sync guarantees we really have data to mmap onto to avoid
+ the SIGBUS.
** Changed in: stress-ng (Ubuntu Eoan)
Status: In Progress => Fix Committed
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https://bugs.launchpad.net/bugs/1845011
Title:
mcontend stressor SIGBUS's on older armhf platforms
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