linux-kernel - Re: [PATCH] futex: Remove unnecessary warning from get_futex

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Date:   Tue, 8 Aug 2017 23:49:11 -0700
From:   Davidlohr Bueso <dave@...olabs.net>
To:     Mel Gorman <mgorman@...e.de>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Mark Rutland <mark.rutland@....com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Ingo Molnar <mingo@...nel.org>,
        Davidlohr Bueso <dbueso@...e.de>,
        Hugh Dickins <hughd@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] futex: Remove unnecessary warning from get_futex_key

On Wed, 09 Aug 2017, Mel Gorman wrote:

>@@ -676,7 +676,7 @@ get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key, int rw)
> 		 * cases, therefore a successful atomic_inc return below will
> 		 * guarantee that get_futex_key() will still imply smp_mb(); (B).

You missed the comment above.

diff --git a/kernel/futex.c b/kernel/futex.c
index 16dbe4c93895..6b4a6a7cad3d 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -670,13 +670,14 @@ get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key, int rw)
 		 * this reference was taken by ihold under the page lock
 		 * pinning the inode in place so i_lock was unnecessary. The
 		 * only way for this check to fail is if the inode was
-		 * truncated in parallel so warn for now if this happens.
+		 * truncated in parallel -- which is a bizarre scenario, in
+		 * any case, just retry.
 		 *
 		 * We are not calling into get_futex_key_refs() in file-backed
 		 * cases, therefore a successful atomic_inc return below will
 		 * guarantee that get_futex_key() will still imply smp_mb(); (B).
 		 */
-		if (WARN_ON_ONCE(!atomic_inc_not_zero(&inode->i_count))) {
+		if (!atomic_inc_not_zero(&inode->i_count)) {
 			rcu_read_unlock();
 			put_page(page);
 

Thanks,
Davidlohr