linux-kernel - Re: [PATCH 08/10] iommu/amd: drop the lock while allocating new irq remap table

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Message-ID: <20180315125832.kfxoqfnxdajeg2yl@8bytes.org>
Date:   Thu, 15 Mar 2018 13:58:32 +0100
From:   Joerg Roedel <joro@...tes.org>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        tglx@...utronix.de
Subject: Re: [PATCH 08/10] iommu/amd: drop the lock while allocating new irq
 remap table

On Fri, Feb 23, 2018 at 11:27:34PM +0100, Sebastian Andrzej Siewior wrote:
> The irq_remap_table is allocated while the iommu_table_lock is held with
> interrupts disabled. While this works it makes RT scream very loudly.
> >From looking at the call sites, all callers are in the early device
> initialisation (apic_bsp_setup(), pci_enable_device(),
> pci_enable_msi()) so make sense to drop the lock which also enables
> interrupts and try to allocate that memory with GFP_KERNEL instead
> GFP_ATOMIC.
> 
> Since during the allocation the iommu_table_lock is dropped, we need to
> recheck if table exists after the lock has been reacquired. I *think*
> that it is impossible that the "devid" entry appears in irq_lookup_table
> while the lock is dropped since the same device can only be probed once.
> It is more likely that another device added an `alias' entry. However I
> check for both cases, just to be sure.
> 
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>

This looks like it conflicts with the x86/amd branch as well.