Re: [PATCH] infiniband: fix a subtle race condition

From: Cong Wang
Date: Thu Jun 14 2018 - 02:22:20 EST

On Wed, Jun 13, 2018 at 10:34 PM, Leon Romanovsky <leon@xxxxxxxxxx> wrote:
> Hi Cong,
> If the compiler optimizes the first line (mutex_lock) as you wrote,
> it will reuse "f" for the second line (mutex_unlock) too.

Nope, check the assembly if you don't trust me, at least
my compiler always fetches ctx->file without this patch.

I can show you the assembly code tomorrow (too late to
access my dev machine now).

> You need to ensure that ucma_modify_id() doesn't run in parallel to
> anything that uses "ctx->file" directly and indirectly.

Talk is easy, show me the code. :) I knew there is probably
some other race with this code even after my patch, possibly with
->close() for example, but for this specific unlock warning, this patch
is sufficient. I can't solve all the races in one patch.