On Thu, Sep 1, 2022 at 11:23 PM Sebastian Andrzej Siewior
[off-list ref] wrote:

On 2022-09-01 16:24:09 [-0400], Kent Overstreet wrote:

quoted

quoted

--- a/include/linux/mmap_lock.h
+++ b/include/linux/mmap_lock.h

@@ -60,6 +60,18 @@ static inline void __mmap_lock_trace_released(struct mm_struct *mm, bool write)

 #endif /* CONFIG_TRACING */

+static inline void mmap_assert_locked(struct mm_struct *mm)
+{
+   lockdep_assert_held(&mm->mmap_lock);
+   VM_BUG_ON_MM(!rwsem_is_locked(&mm->mmap_lock), mm);

These look redundant to me - maybe there's a reason the VM developers want both,
but I would drop the VM_BUG_ON() and just keep the lockdep_assert_held(), since
that's the standard way to write that assertion.

Exactly. rwsem_is_locked() returns true only if the lock is "locked" not
necessary by the caller. lockdep_assert_held() checks that the lock is
locked by the caller - this is the important part.

Ok, if at the end of the day there is a consensus that this redundancy
should be removed then I'll do that in a patch separate from this
series. Please note that in this patch I'm not changing these
functions in any way, just moving them.

Sebastian

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