From: Al Viro <viro@ZenIV.linux.org.uk>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Benjamin LaHaise <bcrl@kvack.org>, Jeff Moyer <jmoyer@redhat.com>,
linux-aio@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 0/3] aio: ctx->dead cleanups
Date: Wed, 17 Jun 2015 01:39:06 +0100 [thread overview]
Message-ID: <20150617003906.GC17109@ZenIV.linux.org.uk> (raw)
In-Reply-To: <20150616230414.GA15776@redhat.com>
On Wed, Jun 17, 2015 at 01:04:14AM +0200, Oleg Nesterov wrote:
> Al, please help. We are trying to backport some aio fixes and I am
> absolutely confused by your b2edffdd912b "fix mremap() vs. ioctx_kill()
> race".
>
>
> Firstly, I simply can't understand what exactly it tries to fix. OK,
> aio_free_ring() can race with kill and we can remap the soon-to-be-killed
> ctx. So what? kill_ioctx() will the the correct (already re-mapped)
> ctx->mmap_base after it drops mm->ioctx_lock.
Huh? kill_ioctx() picks ctx->mmap_base and passes it to vm_munmap().
Which tries to grab mmap_sem, blocks for mremap() from another thread
and waits for it to drop mmap_sem. By that time ctx->mmap_base has
nothing whatsoever to the argument we'd passed to vm_munmap(). Sure,
it had been recalculated by aio_ring_remap(), but it's too late for
us - we'd already fetched the old value.
next prev parent reply other threads:[~2015-06-17 0:39 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-06-16 23:04 [PATCH 0/3] aio: ctx->dead cleanups Oleg Nesterov
2015-06-16 23:04 ` [PATCH 1/3] aio_ring_remap: turn the ctx->dead check into WARN_ON() Oleg Nesterov
2015-06-17 17:50 ` Jeff Moyer
2015-06-17 18:42 ` Oleg Nesterov
2015-06-16 23:04 ` [PATCH 2/3] aio: make aio_ring->dead boolean Oleg Nesterov
2015-06-16 23:50 ` [PATCH v2 " Oleg Nesterov
2015-06-17 19:33 ` Jeff Moyer
2015-06-16 23:04 ` [PATCH 3/3] aio_free_ring: don't do page_count(NULL) Oleg Nesterov
2015-06-17 18:26 ` Jeff Moyer
2015-06-17 0:39 ` Al Viro [this message]
2015-06-17 0:50 ` [PATCH 0/3] aio: ctx->dead cleanups Al Viro
2015-06-17 1:22 ` Oleg Nesterov
2015-06-18 16:08 ` Oleg Nesterov
2015-06-17 1:05 ` Oleg Nesterov
2015-06-17 1:14 ` Oleg Nesterov
2015-06-17 1:32 ` Oleg Nesterov
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