Re: [RFC PATCH] lib: Introduce generic __cmpxchg_u64() and use it where needed
From: Paul E. McKenney <hidden>
Date: 2018-11-01 20:29:23
Also in:
linux-mips, linux-nfs, lkml, netdev
On Thu, Nov 01, 2018 at 06:27:39PM +0100, Peter Zijlstra wrote:
On Thu, Nov 01, 2018 at 06:14:32PM +0100, Peter Zijlstra wrote:quoted
quoted
This reminds me of this sooooo silly patch :/ https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=adb03115f4590baa280ddc440a8eff08a6be0cb7You'd probably want to write it like so; +- some ordering stuff, that code didn't look like it really needs the memory barriers implied by these, but I didn't look too hard.
The atomic_fetch_add() API would need to be propagated out to the other architectures, correct? Thanx, Paul
quoted hunk ↗ jump to hunk
diff --git a/net/ipv4/route.c b/net/ipv4/route.c index c0a9d26c06ce..11deb1d7e96b 100644 --- a/net/ipv4/route.c +++ b/net/ipv4/route.c@@ -485,16 +485,10 @@ u32 ip_idents_reserve(u32 hash, int segs) u32 now = (u32)jiffies; u32 new, delta = 0; - if (old != now && cmpxchg(p_tstamp, old, now) == old) + if (old != now && try_cmpxchg(p_tstamp, &old, now)) delta = prandom_u32_max(now - old); - /* Do not use atomic_add_return() as it makes UBSAN unhappy */ - do { - old = (u32)atomic_read(p_id); - new = old + delta + segs; - } while (atomic_cmpxchg(p_id, old, new) != old); - - return new - segs; + return atomic_fetch_add(segs + delta, p_id) + delta; } EXPORT_SYMBOL(ip_idents_reserve);