linux-kernel - [PATCH AUTOSEL 4.19 03/16] s390/mm: Add cond_resched() to cmm_alloc/free

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Message-ID: <20241004183150.3676355-3-sashal@kernel.org>
Date: Fri,  4 Oct 2024 14:31:30 -0400
From: Sasha Levin <sashal@...nel.org>
To: linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Cc: Gerald Schaefer <gerald.schaefer@...ux.ibm.com>,
	Heiko Carstens <hca@...ux.ibm.com>,
	Sasha Levin <sashal@...nel.org>,
	agordeev@...ux.ibm.com,
	gor@...ux.ibm.com,
	linux-s390@...r.kernel.org
Subject: [PATCH AUTOSEL 4.19 03/16] s390/mm: Add cond_resched() to cmm_alloc/free_pages()

From: Gerald Schaefer <gerald.schaefer@...ux.ibm.com>

[ Upstream commit 131b8db78558120f58c5dc745ea9655f6b854162 ]

Adding/removing large amount of pages at once to/from the CMM balloon
can result in rcu_sched stalls or workqueue lockups, because of busy
looping w/o cond_resched().

Prevent this by adding a cond_resched(). cmm_free_pages() holds a
spin_lock while looping, so it cannot be added directly to the existing
loop. Instead, introduce a wrapper function that operates on maximum 256
pages at once, and add it there.

Signed-off-by: Gerald Schaefer <gerald.schaefer@...ux.ibm.com>
Reviewed-by: Heiko Carstens <hca@...ux.ibm.com>
Signed-off-by: Heiko Carstens <hca@...ux.ibm.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 arch/s390/mm/cmm.c | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/arch/s390/mm/cmm.c b/arch/s390/mm/cmm.c
index a51c892f14f3e..756aefbd05249 100644
--- a/arch/s390/mm/cmm.c
+++ b/arch/s390/mm/cmm.c
@@ -98,11 +98,12 @@ static long cmm_alloc_pages(long nr, long *counter,
 		(*counter)++;
 		spin_unlock(&cmm_lock);
 		nr--;
+		cond_resched();
 	}
 	return nr;
 }
 
-static long cmm_free_pages(long nr, long *counter, struct cmm_page_array **list)
+static long __cmm_free_pages(long nr, long *counter, struct cmm_page_array **list)
 {
 	struct cmm_page_array *pa;
 	unsigned long addr;
@@ -126,6 +127,21 @@ static long cmm_free_pages(long nr, long *counter, struct cmm_page_array **list)
 	return nr;
 }
 
+static long cmm_free_pages(long nr, long *counter, struct cmm_page_array **list)
+{
+	long inc = 0;
+
+	while (nr) {
+		inc = min(256L, nr);
+		nr -= inc;
+		inc = __cmm_free_pages(inc, counter, list);
+		if (inc)
+			break;
+		cond_resched();
+	}
+	return nr + inc;
+}
+
 static int cmm_oom_notify(struct notifier_block *self,
 			  unsigned long dummy, void *parm)
 {
-- 
2.43.0