From: "J. Bruce Fields" <bfields@fieldses.org>
To: NeilBrown <neilb@suse.com>
Cc: Jeff Layton <jlayton@kernel.org>,
Alexander Viro <viro@zeniv.linux.org.uk>,
Martin Wilck <mwilck@suse.de>,
linux-fsdevel@vger.kernel.org,
Frank Filz <ffilzlnx@mindspring.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 0/5 - V2] locks: avoid thundering-herd wake-ups
Date: Thu, 9 Aug 2018 13:32:45 -0400 [thread overview]
Message-ID: <20180809173245.GM23873@fieldses.org> (raw)
In-Reply-To: <153378012255.1220.6754153662007899557.stgit@noble>
I think there's also a problem with multiple tasks sharing the same
lock owner.
So, all locks are exclusive locks for the same range. We have four
tasks. Tasks 1 and 4 share the same owner, the others' owners are
distinct.
- Task 1 gets a lock.
- Task 2 gets a conflicting lock.
- Task 3 gets another conflicting lock. So now we the tree is
3->2->1.
- Task 1's lock is released.
- Before task 2 is scheduled, task 4 acquires a new lock.
- Task 2 waits on task 4's lock, we now have
3->2->4.
Task 3 shouldn't be waiting--the lock it's requesting has the same owner
as the lock task 4 holds--but we fail to wake up task 3.
--b.
next prev parent reply other threads:[~2018-08-09 19:58 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-08-09 2:04 [PATCH 0/5 - V2] locks: avoid thundering-herd wake-ups NeilBrown
2018-08-09 2:04 ` [PATCH 2/5] fs/locks: allow a lock request to block other requests NeilBrown
2018-08-09 2:04 ` [PATCH 5/5] fs/locks: create a tree of dependent requests NeilBrown
2018-08-09 11:17 ` Jeff Layton
2018-08-09 23:25 ` NeilBrown
2018-08-09 14:13 ` J. Bruce Fields
2018-08-09 22:19 ` NeilBrown
2018-08-10 0:36 ` J. Bruce Fields
2018-08-09 2:04 ` [PATCH 1/5] fs/locks: rename some lists and pointers NeilBrown
2018-08-09 2:04 ` [PATCH 4/5] fs/locks: split out __locks_wake_one() NeilBrown
2018-08-09 2:04 ` [PATCH 3/5] fs/locks: change all *_conflict() functions to return a new enum NeilBrown
2018-08-09 11:09 ` Jeff Layton
2018-08-09 13:09 ` J. Bruce Fields
2018-08-09 23:40 ` NeilBrown
2018-08-10 0:56 ` J. Bruce Fields
2018-08-09 17:32 ` J. Bruce Fields [this message]
2018-08-09 22:12 ` [PATCH 0/5 - V2] locks: avoid thundering-herd wake-ups NeilBrown
2018-08-10 0:29 ` J. Bruce Fields
2018-08-10 1:50 ` NeilBrown
2018-08-10 2:52 ` J. Bruce Fields
2018-08-10 3:17 ` NeilBrown
2018-08-10 15:47 ` J. Bruce Fields
2018-08-11 11:56 ` Jeff Layton
2018-08-11 12:35 ` J. Bruce Fields
2018-08-11 11:51 ` Jeff Layton
2018-08-11 12:21 ` J. Bruce Fields
2018-08-11 13:15 ` Jeff Layton
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