Turns out that commit 9ec23531fd48 ("sched/preempt, mm/fault: Trigger
might_sleep() in might_fault() with disabled pagefaults") accidentally
(and unnessecarily) put the lockdep part of __might_fault() under
CONFIG_DEBUG_ATOMIC_SLEEP.

Cc: David Hildenbrand <david@redhat.com>
Fixes: 9ec23531fd48 ("sched/preempt, mm/fault: Trigger might_sleep() in might_fault() with disabled pagefaults")
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 mm/memory.c |    2 --
 1 file changed, 2 deletions(-)

--- a/mm/memory.c
+++ b/mm/memory.c
@@ -6695,10 +6695,8 @@ void __might_fault(const char *file, int
 	if (pagefault_disabled())
 		return;
 	__might_sleep(file, line);
-#if defined(CONFIG_DEBUG_ATOMIC_SLEEP)
 	if (current->mm)
 		might_lock_read(&current->mm->mmap_lock);
-#endif
 }
 EXPORT_SYMBOL(__might_fault);
 #endif

The following commit has been merged into the locking/core branch of tip:

Commit-ID:     a1b65f3f7c6f7f0a08a7dba8be458c6415236487
Gitweb:        https://git.kernel.org/tip/a1b65f3f7c6f7f0a08a7dba8be458c6415236487
Author:        Peter Zijlstra <peterz@infradead.org>
AuthorDate:    Mon, 04 Nov 2024 14:39:10 +01:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Sat, 01 Mar 2025 19:32:41 +01:00

lockdep/mm: Fix might_fault() lockdep check of current->mm->mmap_lock

Turns out that this commit, about 10 years ago:

  9ec23531fd48 ("sched/preempt, mm/fault: Trigger might_sleep() in might_fault() with disabled pagefaults")

... accidentally (and unnessecarily) put the lockdep part of
__might_fault() under CONFIG_DEBUG_ATOMIC_SLEEP=y.

This is potentially notable because large distributions such as
Ubuntu are running with !CONFIG_DEBUG_ATOMIC_SLEEP.

Restore the debug check.

[ mingo: Update changelog. ]

Fixes: 9ec23531fd48 ("sched/preempt, mm/fault: Trigger might_sleep() in might_fault() with disabled pagefaults")
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: https://lore.kernel.org/r/20241104135517.536628371@infradead.org
---
 mm/memory.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index 539c0f7..1dfad45 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -6835,10 +6835,8 @@ void __might_fault(const char *file, int line)
 	if (pagefault_disabled())
 		return;
 	__might_sleep(file, line);
-#if defined(CONFIG_DEBUG_ATOMIC_SLEEP)
 	if (current->mm)
 		might_lock_read(&current->mm->mmap_lock);
-#endif
 }
 EXPORT_SYMBOL(__might_fault);
 #endif