[PATCH 5.15 107/691] padata: Honor the callers alignment in case of chunk_size 0

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5.15-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Kamlesh Gurudasani <kamlesh@xxxxxx>

[ Upstream commit 24cc57d8faaa4060fd58adf810b858fcfb71a02f ]

In the case where we are forcing the ps.chunk_size to be at least 1,
we are ignoring the caller's alignment.

Move the forcing of ps.chunk_size to be at least 1 before rounding it
up to caller's alignment, so that caller's alignment is honored.

While at it, use max() to force the ps.chunk_size to be at least 1 to
improve readability.

Fixes: 6d45e1c948a8 ("padata: Fix possible divide-by-0 panic in padata_mt_helper()")
Signed-off-by: Kamlesh Gurudasani <kamlesh@xxxxxx>
Acked-by:  Waiman Long <longman@xxxxxxxxxx>
Acked-by: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx>
Signed-off-by: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 kernel/padata.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/padata.c b/kernel/padata.c
index 7c52f9de5d4ec..f567b54d79639 100644
--- a/kernel/padata.c
+++ b/kernel/padata.c
@@ -503,9 +503,12 @@ void __init padata_do_multithreaded(struct padata_mt_job *job)
 	 * thread function.  Load balance large jobs between threads by
 	 * increasing the number of chunks, guarantee at least the minimum
 	 * chunk size from the caller, and honor the caller's alignment.
+	 * Ensure chunk_size is at least 1 to prevent divide-by-0
+	 * panic in padata_mt_helper().
 	 */
 	ps.chunk_size = job->size / (ps.nworks * load_balance_factor);
 	ps.chunk_size = max(ps.chunk_size, job->min_chunk);
+	ps.chunk_size = max(ps.chunk_size, 1ul);
 	ps.chunk_size = roundup(ps.chunk_size, job->align);
 
 	/*
-- 
2.43.0







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