Revert "cpumask: fix checking valid cpu range".

This reverts commit 78e5a33 ("cpumask: fix checking valid cpu range").

syzbot is hitting WARN_ON_ONCE(cpu >= nr_cpumask_bits) warning at
cpu_max_bits_warn() [1], for commit 78e5a33 ("cpumask: fix checking
valid cpu range") is broken.  Obviously that patch hits WARN_ON_ONCE()
when e.g.  reading /proc/cpuinfo because passing "cpu + 1" instead of
"cpu" will trivially hit cpu == nr_cpumask_bits condition.

Although syzbot found this problem in linux-next.git on 2022/09/27 [2],
this problem was not fixed immediately.  As a result, that patch was
sent to linux.git before the patch author recognizes this problem, and
syzbot started failing to test changes in linux.git since 2022/10/10
[3].

Andrew Jones proposed a fix for x86 and riscv architectures [4].  But
[2] and [5] indicate that affected locations are not limited to arch
code.  More delay before we find and fix affected locations, less tested
kernel (and more difficult to bisect and fix) before release.

We should have inspected and fixed basically all cpumask users before
applying that patch.  We should not crash kernels in order to ask
existing cpumask users to update their code, even if limited to
CONFIG_DEBUG_PER_CPU_MAPS=y case.

Link: https://syzkaller.appspot.com/bug?extid=d0fd2bf0dd6da72496dd [1]
Link: https://syzkaller.appspot.com/bug?extid=21da700f3c9f0bc40150 [2]
Link: https://syzkaller.appspot.com/bug?extid=51a652e2d24d53e75734 [3]
Link: https://lkml.kernel.org/r/[email protected] [4]
Link: https://syzkaller.appspot.com/bug?extid=4d46c43d81c3bd155060 [5]
Reported-by: Andrew Jones <[email protected]>
Reported-by: [email protected]
Signed-off-by: Tetsuo Handa <[email protected]>
Cc: Yury Norov <[email protected]>
Cc: Borislav Petkov <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Author: Tetsuo Handa

include/linux/cpumask.h

@@ -174,8 +174,9 @@ static inline unsigned int cpumask_last(const struct cpumask *srcp)
 static inline
 unsigned int cpumask_next(int n, const struct cpumask *srcp)
 {
-	/* n is a prior cpu */
-	cpumask_check(n + 1);
+	/* -1 is a legal arg here. */
+	if (n != -1)
+		cpumask_check(n);
 	return find_next_bit(cpumask_bits(srcp), nr_cpumask_bits, n + 1);
 }
 
@@ -188,8 +189,9 @@ unsigned int cpumask_next(int n, const struct cpumask *srcp)
  */
 static inline unsigned int cpumask_next_zero(int n, const struct cpumask *srcp)
 {
-	/* n is a prior cpu */
-	cpumask_check(n + 1);
+	/* -1 is a legal arg here. */
+	if (n != -1)
+		cpumask_check(n);
 	return find_next_zero_bit(cpumask_bits(srcp), nr_cpumask_bits, n+1);
 }
 
@@ -229,8 +231,9 @@ static inline
 unsigned int cpumask_next_and(int n, const struct cpumask *src1p,
 		     const struct cpumask *src2p)
 {
-	/* n is a prior cpu */
-	cpumask_check(n + 1);
+	/* -1 is a legal arg here. */
+	if (n != -1)
+		cpumask_check(n);
 	return find_next_and_bit(cpumask_bits(src1p), cpumask_bits(src2p),
 		nr_cpumask_bits, n + 1);
 }
@@ -260,8 +263,8 @@ static inline
 unsigned int cpumask_next_wrap(int n, const struct cpumask *mask, int start, bool wrap)
 {
 	cpumask_check(start);
-	/* n is a prior cpu */
-	cpumask_check(n + 1);
+	if (n != -1)
+		cpumask_check(n);
 
 	/*
 	 * Return the first available CPU when wrapping, or when starting before cpu0,