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    Subject[PATCH 4.19 251/287] powerpc/pci: Fix get_phb_number() locking
    Date
    From: Michael Ellerman <mpe@ellerman.id.au>

    commit 8d48562a2729742f767b0fdd994d6b2a56a49c63 upstream.

    The recent change to get_phb_number() causes a DEBUG_ATOMIC_SLEEP
    warning on some systems:

    BUG: sleeping function called from invalid context at kernel/locking/mutex.c:580
    in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 1, name: swapper
    preempt_count: 1, expected: 0
    RCU nest depth: 0, expected: 0
    1 lock held by swapper/1:
    #0: c157efb0 (hose_spinlock){+.+.}-{2:2}, at: pcibios_alloc_controller+0x64/0x220
    Preemption disabled at:
    [<00000000>] 0x0
    CPU: 0 PID: 1 Comm: swapper Not tainted 5.19.0-yocto-standard+ #1
    Call Trace:
    [d101dc90] [c073b264] dump_stack_lvl+0x50/0x8c (unreliable)
    [d101dcb0] [c0093b70] __might_resched+0x258/0x2a8
    [d101dcd0] [c0d3e634] __mutex_lock+0x6c/0x6ec
    [d101dd50] [c0a84174] of_alias_get_id+0x50/0xf4
    [d101dd80] [c002ec78] pcibios_alloc_controller+0x1b8/0x220
    [d101ddd0] [c140c9dc] pmac_pci_init+0x198/0x784
    [d101de50] [c140852c] discover_phbs+0x30/0x4c
    [d101de60] [c0007fd4] do_one_initcall+0x94/0x344
    [d101ded0] [c1403b40] kernel_init_freeable+0x1a8/0x22c
    [d101df10] [c00086e0] kernel_init+0x34/0x160
    [d101df30] [c001b334] ret_from_kernel_thread+0x5c/0x64

    This is because pcibios_alloc_controller() holds hose_spinlock but
    of_alias_get_id() takes of_mutex which can sleep.

    The hose_spinlock protects the phb_bitmap, and also the hose_list, but
    it doesn't need to be held while get_phb_number() calls the OF routines,
    because those are only looking up information in the device tree.

    So fix it by having get_phb_number() take the hose_spinlock itself, only
    where required, and then dropping the lock before returning.
    pcibios_alloc_controller() then needs to take the lock again before the
    list_add() but that's safe, the order of the list is not important.

    Fixes: 0fe1e96fef0a ("powerpc/pci: Prefer PCI domain assignment via DT 'linux,pci-domain' and alias")
    Reported-by: Guenter Roeck <linux@roeck-us.net>
    Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
    Link: https://lore.kernel.org/r/20220815065550.1303620-1-mpe@ellerman.id.au
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    arch/powerpc/kernel/pci-common.c | 16 ++++++++++------
    1 file changed, 10 insertions(+), 6 deletions(-)

    --- a/arch/powerpc/kernel/pci-common.c
    +++ b/arch/powerpc/kernel/pci-common.c
    @@ -75,10 +75,6 @@ const struct dma_map_ops *get_pci_dma_op
    }
    EXPORT_SYMBOL(get_pci_dma_ops);

    -/*
    - * This function should run under locking protection, specifically
    - * hose_spinlock.
    - */
    static int get_phb_number(struct device_node *dn)
    {
    int ret, phb_id = -1;
    @@ -115,15 +111,20 @@ static int get_phb_number(struct device_
    if (!ret)
    phb_id = (int)(prop & (MAX_PHBS - 1));

    + spin_lock(&hose_spinlock);
    +
    /* We need to be sure to not use the same PHB number twice. */
    if ((phb_id >= 0) && !test_and_set_bit(phb_id, phb_bitmap))
    - return phb_id;
    + goto out_unlock;

    /* If everything fails then fallback to dynamic PHB numbering. */
    phb_id = find_first_zero_bit(phb_bitmap, MAX_PHBS);
    BUG_ON(phb_id >= MAX_PHBS);
    set_bit(phb_id, phb_bitmap);

    +out_unlock:
    + spin_unlock(&hose_spinlock);
    +
    return phb_id;
    }

    @@ -134,10 +135,13 @@ struct pci_controller *pcibios_alloc_con
    phb = zalloc_maybe_bootmem(sizeof(struct pci_controller), GFP_KERNEL);
    if (phb == NULL)
    return NULL;
    - spin_lock(&hose_spinlock);
    +
    phb->global_number = get_phb_number(dev);
    +
    + spin_lock(&hose_spinlock);
    list_add_tail(&phb->list_node, &hose_list);
    spin_unlock(&hose_spinlock);
    +
    phb->dn = dev;
    phb->is_dynamic = slab_is_available();
    #ifdef CONFIG_PPC64

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