linux-kernel - [PATCH v4 1/3] mmap locking API: add mmap_lock_is

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Date:   Tue, 18 Aug 2020 09:58:16 +0800
From:   Chinwen Chang <chinwen.chang@...iatek.com>
To:     Matthias Brugger <matthias.bgg@...il.com>,
        Michel Lespinasse <walken@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Daniel Jordan <daniel.m.jordan@...cle.com>,
        Davidlohr Bueso <dbueso@...e.de>,
        Chinwen Chang <chinwen.chang@...iatek.com>,
        Alexey Dobriyan <adobriyan@...il.com>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Steven Price <steven.price@....com>,
        Song Liu <songliubraving@...com>,
        Jimmy Assarsson <jimmyassarsson@...il.com>,
        Huang Ying <ying.huang@...el.com>,
        Daniel Kiss <daniel.kiss@....com>,
        Laurent Dufour <ldufour@...ux.ibm.com>
CC:     <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-mediatek@...ts.infradead.org>,
        <linux-fsdevel@...r.kernel.org>, <wsd_upstream@...iatek.com>
Subject: [PATCH v4 1/3] mmap locking API: add mmap_lock_is_contended()

Add new API to query if someone wants to acquire mmap_lock
for write attempts.

Using this instead of rwsem_is_contended makes it more tolerant
of future changes to the lock type.

Signed-off-by: Chinwen Chang <chinwen.chang@...iatek.com>
Reviewed-by: Steven Price <steven.price@....com>
Acked-by: Michel Lespinasse <walken@...gle.com>
---
 include/linux/mmap_lock.h | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/include/linux/mmap_lock.h b/include/linux/mmap_lock.h
index 0707671..18e7eae 100644
--- a/include/linux/mmap_lock.h
+++ b/include/linux/mmap_lock.h
@@ -87,4 +87,9 @@ static inline void mmap_assert_write_locked(struct mm_struct *mm)
 	VM_BUG_ON_MM(!rwsem_is_locked(&mm->mmap_lock), mm);
 }
 
+static inline int mmap_lock_is_contended(struct mm_struct *mm)
+{
+	return rwsem_is_contended(&mm->mmap_lock);
+}
+
 #endif /* _LINUX_MMAP_LOCK_H */
-- 
1.9.1