+ padata-honor-the-callers-alignment-in-case-of-chunk_size-0.patch added to mm-hotfixes-unstable branch

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The patch titled
     Subject: padata: honor the caller's alignment in case of chunk_size 0
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     padata-honor-the-callers-alignment-in-case-of-chunk_size-0.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/padata-honor-the-callers-alignment-in-case-of-chunk_size-0.patch

This patch will later appear in the mm-hotfixes-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Kamlesh Gurudasani <kamlesh@xxxxxx>
Subject: padata: honor the caller's alignment in case of chunk_size 0
Date: Thu, 22 Aug 2024 02:32:52 +0530

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.

Link: https://lkml.kernel.org/r/20240822-max-v1-1-cb4bc5b1c101@xxxxxx
Fixes: 6d45e1c948a8 ("padata: Fix possible divide-by-0 panic in padata_mt_helper()")
Signed-off-by: Kamlesh Gurudasani <kamlesh@xxxxxx>
Cc: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx>
Cc: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Cc: Steffen Klassert <steffen.klassert@xxxxxxxxxxx>
Cc: Waiman Long <longman@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 kernel/padata.c |   12 ++++--------
 1 file changed, 4 insertions(+), 8 deletions(-)

--- a/kernel/padata.c~padata-honor-the-callers-alignment-in-case-of-chunk_size-0
+++ a/kernel/padata.c
@@ -509,21 +509,17 @@ void __init padata_do_multithreaded(stru
 
 	/*
 	 * Chunk size is the amount of work a helper does per call to the
-	 * thread function.  Load balance large jobs between threads by
+	 * 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);
 
-	/*
-	 * chunk_size can be 0 if the caller sets min_chunk to 0. So force it
-	 * to at least 1 to prevent divide-by-0 panic in padata_mt_helper().`
-	 */
-	if (!ps.chunk_size)
-		ps.chunk_size = 1U;
-
 	list_for_each_entry(pw, &works, pw_list)
 		if (job->numa_aware) {
 			int old_node = atomic_read(&last_used_nid);
_

Patches currently in -mm which might be from kamlesh@xxxxxx are

padata-honor-the-callers-alignment-in-case-of-chunk_size-0.patch





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