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    Subject[PATCH AUTOSEL 4.14 08/26] mm/memory_hotplug: make add_memory() take the device_hotplug_lock
    Date
    From: David Hildenbrand <david@redhat.com>

    [ Upstream commit 8df1d0e4a265f25dc1e7e7624ccdbcb4a6630c89 ]

    add_memory() currently does not take the device_hotplug_lock, however
    is aleady called under the lock from
    arch/powerpc/platforms/pseries/hotplug-memory.c
    drivers/acpi/acpi_memhotplug.c
    to synchronize against CPU hot-remove and similar.

    In general, we should hold the device_hotplug_lock when adding memory to
    synchronize against online/offline request (e.g. from user space) - which
    already resulted in lock inversions due to device_lock() and
    mem_hotplug_lock - see 30467e0b3be ("mm, hotplug: fix concurrent memory
    hot-add deadlock"). add_memory()/add_memory_resource() will create memory
    block devices, so this really feels like the right thing to do.

    Holding the device_hotplug_lock makes sure that a memory block device
    can really only be accessed (e.g. via .online/.state) from user space,
    once the memory has been fully added to the system.

    The lock is not held yet in
    drivers/xen/balloon.c
    arch/powerpc/platforms/powernv/memtrace.c
    drivers/s390/char/sclp_cmd.c
    drivers/hv/hv_balloon.c
    So, let's either use the locked variants or take the lock.

    Don't export add_memory_resource(), as it once was exported to be used by
    XEN, which is never built as a module. If somebody requires it, we also
    have to export a locked variant (as device_hotplug_lock is never
    exported).

    Link: http://lkml.kernel.org/r/20180925091457.28651-3-david@redhat.com
    Signed-off-by: David Hildenbrand <david@redhat.com>
    Reviewed-by: Pavel Tatashin <pavel.tatashin@microsoft.com>
    Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
    Reviewed-by: Rashmica Gupta <rashmica.g@gmail.com>
    Reviewed-by: Oscar Salvador <osalvador@suse.de>
    Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
    Cc: Paul Mackerras <paulus@samba.org>
    Cc: Michael Ellerman <mpe@ellerman.id.au>
    Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
    Cc: Len Brown <lenb@kernel.org>
    Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
    Cc: Juergen Gross <jgross@suse.com>
    Cc: Nathan Fontenot <nfont@linux.vnet.ibm.com>
    Cc: John Allen <jallen@linux.vnet.ibm.com>
    Cc: Michal Hocko <mhocko@suse.com>
    Cc: Dan Williams <dan.j.williams@intel.com>
    Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
    Cc: Vlastimil Babka <vbabka@suse.cz>
    Cc: Mathieu Malaterre <malat@debian.org>
    Cc: Pavel Tatashin <pavel.tatashin@microsoft.com>
    Cc: YASUAKI ISHIMATSU <yasu.isimatu@gmail.com>
    Cc: Balbir Singh <bsingharora@gmail.com>
    Cc: Haiyang Zhang <haiyangz@microsoft.com>
    Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
    Cc: Jonathan Corbet <corbet@lwn.net>
    Cc: Kate Stewart <kstewart@linuxfoundation.org>
    Cc: "K. Y. Srinivasan" <kys@microsoft.com>
    Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
    Cc: Michael Neuling <mikey@neuling.org>
    Cc: Philippe Ombredanne <pombredanne@nexb.com>
    Cc: Stephen Hemminger <sthemmin@microsoft.com>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    .../platforms/pseries/hotplug-memory.c | 2 +-
    drivers/acpi/acpi_memhotplug.c | 2 +-
    drivers/base/memory.c | 9 ++++++--
    drivers/xen/balloon.c | 3 +++
    include/linux/memory_hotplug.h | 1 +
    mm/memory_hotplug.c | 22 ++++++++++++++++---
    6 files changed, 32 insertions(+), 7 deletions(-)

    diff --git a/arch/powerpc/platforms/pseries/hotplug-memory.c b/arch/powerpc/platforms/pseries/hotplug-memory.c
    index 1d48ab424bd9..c197ea8dde01 100644
    --- a/arch/powerpc/platforms/pseries/hotplug-memory.c
    +++ b/arch/powerpc/platforms/pseries/hotplug-memory.c
    @@ -784,7 +784,7 @@ static int dlpar_add_lmb(struct of_drconf_cell *lmb)
    nid = memory_add_physaddr_to_nid(lmb->base_addr);

    /* Add the memory */
    - rc = add_memory(nid, lmb->base_addr, block_sz);
    + rc = __add_memory(nid, lmb->base_addr, block_sz);
    if (rc) {
    dlpar_remove_device_tree_lmb(lmb);
    return rc;
    diff --git a/drivers/acpi/acpi_memhotplug.c b/drivers/acpi/acpi_memhotplug.c
    index 6b0d3ef7309c..2ccfbb61ca89 100644
    --- a/drivers/acpi/acpi_memhotplug.c
    +++ b/drivers/acpi/acpi_memhotplug.c
    @@ -228,7 +228,7 @@ static int acpi_memory_enable_device(struct acpi_memory_device *mem_device)
    if (node < 0)
    node = memory_add_physaddr_to_nid(info->start_addr);

    - result = add_memory(node, info->start_addr, info->length);
    + result = __add_memory(node, info->start_addr, info->length);

    /*
    * If the memory block has been used by the kernel, add_memory()
    diff --git a/drivers/base/memory.c b/drivers/base/memory.c
    index 1d60b58a8c19..9a9aebb4bd19 100644
    --- a/drivers/base/memory.c
    +++ b/drivers/base/memory.c
    @@ -517,15 +517,20 @@ memory_probe_store(struct device *dev, struct device_attribute *attr,
    if (phys_addr & ((pages_per_block << PAGE_SHIFT) - 1))
    return -EINVAL;

    + ret = lock_device_hotplug_sysfs();
    + if (ret)
    + goto out;
    +
    nid = memory_add_physaddr_to_nid(phys_addr);
    - ret = add_memory(nid, phys_addr,
    - MIN_MEMORY_BLOCK_SIZE * sections_per_block);
    + ret = __add_memory(nid, phys_addr,
    + MIN_MEMORY_BLOCK_SIZE * sections_per_block);

    if (ret)
    goto out;

    ret = count;
    out:
    + unlock_device_hotplug();
    return ret;
    }

    diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
    index 065f0b607373..6e39a0c10f93 100644
    --- a/drivers/xen/balloon.c
    +++ b/drivers/xen/balloon.c
    @@ -401,7 +401,10 @@ static enum bp_state reserve_additional_memory(void)
    * callers drop the mutex before trying again.
    */
    mutex_unlock(&balloon_mutex);
    + /* add_memory_resource() requires the device_hotplug lock */
    + lock_device_hotplug();
    rc = add_memory_resource(nid, resource, memhp_auto_online);
    + unlock_device_hotplug();
    mutex_lock(&balloon_mutex);

    if (rc) {
    diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
    index 58e110aee7ab..d36a02935391 100644
    --- a/include/linux/memory_hotplug.h
    +++ b/include/linux/memory_hotplug.h
    @@ -316,6 +316,7 @@ static inline void remove_memory(int nid, u64 start, u64 size) {}

    extern int walk_memory_range(unsigned long start_pfn, unsigned long end_pfn,
    void *arg, int (*func)(struct memory_block *, void *));
    +extern int __add_memory(int nid, u64 start, u64 size);
    extern int add_memory(int nid, u64 start, u64 size);
    extern int add_memory_resource(int nid, struct resource *resource, bool online);
    extern int arch_add_memory(int nid, u64 start, u64 size, bool want_memblock);
    diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
    index d4b5f29906b9..dc60f2f27389 100644
    --- a/mm/memory_hotplug.c
    +++ b/mm/memory_hotplug.c
    @@ -1109,7 +1109,12 @@ static int online_memory_block(struct memory_block *mem, void *arg)
    return device_online(&mem->dev);
    }

    -/* we are OK calling __meminit stuff here - we have CONFIG_MEMORY_HOTPLUG */
    +/*
    + * NOTE: The caller must call lock_device_hotplug() to serialize hotplug
    + * and online/offline operations (triggered e.g. by sysfs).
    + *
    + * we are OK calling __meminit stuff here - we have CONFIG_MEMORY_HOTPLUG
    + */
    int __ref add_memory_resource(int nid, struct resource *res, bool online)
    {
    u64 start, size;
    @@ -1202,9 +1207,9 @@ int __ref add_memory_resource(int nid, struct resource *res, bool online)
    mem_hotplug_done();
    return ret;
    }
    -EXPORT_SYMBOL_GPL(add_memory_resource);

    -int __ref add_memory(int nid, u64 start, u64 size)
    +/* requires device_hotplug_lock, see add_memory_resource() */
    +int __ref __add_memory(int nid, u64 start, u64 size)
    {
    struct resource *res;
    int ret;
    @@ -1218,6 +1223,17 @@ int __ref add_memory(int nid, u64 start, u64 size)
    release_memory_resource(res);
    return ret;
    }
    +
    +int add_memory(int nid, u64 start, u64 size)
    +{
    + int rc;
    +
    + lock_device_hotplug();
    + rc = __add_memory(nid, start, size);
    + unlock_device_hotplug();
    +
    + return rc;
    +}
    EXPORT_SYMBOL_GPL(add_memory);

    #ifdef CONFIG_MEMORY_HOTREMOVE
    --
    2.17.1
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