The patch titled
Subject: test_xarray: fix soft lockup for advanced-api tests
has been added to the -mm mm-unstable branch. Its filename is
test_xarray-add-tests-for-advanced-multi-index-use-fix.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/test_xarray-add-tests-for-advanced-multi-index-use-fix.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Luis Chamberlain <mcgrof@xxxxxxxxxx>
Subject: test_xarray: fix soft lockup for advanced-api tests
Date: Fri, 16 Feb 2024 11:43:29 -0800
The new adanced API tests want to vet the xarray API is doing what it
promises by manually iterating over a set of possible indexes on its
own, and using a query operation which holds the RCU lock and then
releases it. So it is not using the helper loop options which xarray
provides on purpose. Any loop which iterates over 1 million entries
(which is possible with order 20, so emulating say a 4 GiB block size)
to just to rcu lock and unlock will eventually end up triggering a soft
lockup on systems which don't preempt, and have lock provin and RCU
prooving enabled.
xarray users already use XA_CHECK_SCHED for loops which may take a long
time, in our case we don't want to RCU unlock and lock as the caller
does that already, but rather just force a schedule every XA_CHECK_SCHED
iterations since the test is trying to not trust and rather test that
xarray is doing the right thing.
Link: https://lkml.kernel.org/r/20240216194329.840555-1-mcgrof@xxxxxxxxxx
Reported-by: kernel test robot <oliver.sang@xxxxxxxxx>
Closes: https://lkml.kernel.org/r/202402071613.70f28243-lkp@xxxxxxxxx
Signed-off-by: Luis Chamberlain <mcgrof@xxxxxxxxxx>
Cc: Daniel Gomez <da.gomez@xxxxxxxxxxx>
Cc: Luis Chamberlain <mcgrof@xxxxxxxxxx>
Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Cc: Pankaj Raghav <p.raghav@xxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
lib/test_xarray.c | 12 ++++++++++++
1 file changed, 12 insertions(+)
--- a/lib/test_xarray.c~test_xarray-add-tests-for-advanced-multi-index-use-fix
+++ a/lib/test_xarray.c
@@ -728,6 +728,7 @@ static noinline void *test_get_entry(str
{
XA_STATE(xas, xa, index);
void *p;
+ static unsigned int i = 0;
rcu_read_lock();
repeat:
@@ -737,6 +738,17 @@ repeat:
goto repeat;
rcu_read_unlock();
+ /*
+ * This is not part of the page cache, this selftest is pretty
+ * aggressive and does not want to trust the xarray API but rather
+ * test it, and for order 20 (4 GiB block size) we can loop over
+ * over a million entries which can cause a soft lockup. Page cache
+ * APIs won't be stupid, proper page cache APIs loop over the proper
+ * order so when using a larger order we skip shared entries.
+ */
+ if (++i % XA_CHECK_SCHED == 0)
+ schedule();
+
return p;
}
_
Patches currently in -mm which might be from mcgrof@xxxxxxxxxx are
test_xarray-add-tests-for-advanced-multi-index-use.patch
test_xarray-add-tests-for-advanced-multi-index-use-fix.patch
