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SubjectRe: Question about memory leak detector giving false positive report for net/core/flow.c
From
2011/9/27 Eric Dumazet <eric.dumazet@gmail.com>:
> Le lundi 26 septembre 2011 à 17:50 +0100, Catalin Marinas a écrit :
>> On Mon, Sep 26, 2011 at 05:32:54PM +0100, Eric Dumazet wrote:
>> > Le lundi 26 septembre 2011 à 23:17 +0800, Huajun Li a écrit :
>> > > Memory leak detector gives following memory leak report, it seems the
>> > > report is triggered by net/core/flow.c, but actually, it should be a
>> > > false positive report.
>> > > So, is there any idea from kmemleak side to fix/disable this false
>> > > positive report like this?
>> > > Yes, kmemleak_not_leak(...) could disable it, but is it suitable for this case ?
>> ...
>> > CC lkml and percpu maintainers (Tejun Heo & Christoph Lameter ) as well
>> >
>> > AFAIK this false positive only occurs if percpu data is allocated
>> > outside of embedded pcu space.
>> >
>> >  (grep pcpu_get_vm_areas /proc/vmallocinfo)
>> >
>> > I suspect this is a percpu/kmemleak cooperation problem (a missing
>> > kmemleak_alloc() ?)
>> >
>> > I am pretty sure kmemleak_not_leak() is not the right answer to this
>> > problem.
>>
>> kmemleak_not_leak() definitely not the write answer. The alloc_percpu()
>> call does not have any kmemleak_alloc() callback, so it doesn't scan
>> them.
>>
>> Huajun, could you please try the patch below:
>>
>> 8<--------------------------------
>> kmemleak: Handle percpu memory allocation
>>
>> From: Catalin Marinas <catalin.marinas@arm.com>
>>
>> This patch adds kmemleak callbacks from the percpu allocator, reducing a
>> number of false positives caused by kmemleak not scanning such memory
>> blocks.
>>
>> Reported-by: Huajun Li <huajun.li.lee@gmail.com>
>> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
>> ---
>>  mm/percpu.c |   11 +++++++++--
>>  1 files changed, 9 insertions(+), 2 deletions(-)
>>
>> diff --git a/mm/percpu.c b/mm/percpu.c
>> index bf80e55..c47a90b 100644
>> --- a/mm/percpu.c
>> +++ b/mm/percpu.c
>> @@ -67,6 +67,7 @@
>>  #include <linux/spinlock.h>
>>  #include <linux/vmalloc.h>
>>  #include <linux/workqueue.h>
>> +#include <linux/kmemleak.h>
>>
>>  #include <asm/cacheflush.h>
>>  #include <asm/sections.h>
>> @@ -833,7 +834,9 @@ fail_unlock_mutex:
>>   */
>>  void __percpu *__alloc_percpu(size_t size, size_t align)
>>  {
>> -     return pcpu_alloc(size, align, false);
>> +     void __percpu *ptr = pcpu_alloc(size, align, false);
>> +     kmemleak_alloc(ptr, size, 1, GFP_KERNEL);
>> +     return ptr;
>>  }
>>  EXPORT_SYMBOL_GPL(__alloc_percpu);
>>
>> @@ -855,7 +858,9 @@ EXPORT_SYMBOL_GPL(__alloc_percpu);
>>   */
>>  void __percpu *__alloc_reserved_percpu(size_t size, size_t align)
>>  {
>> -     return pcpu_alloc(size, align, true);
>> +     void __percpu *ptr = pcpu_alloc(size, align, true);
>> +     kmemleak_alloc(ptr, size, 1, GFP_KERNEL);
>> +     return ptr;
>>  }
>>
>>  /**
>> @@ -915,6 +920,8 @@ void free_percpu(void __percpu *ptr)
>>       if (!ptr)
>>               return;
>>
>> +     kmemleak_free(ptr);
>> +
>>       addr = __pcpu_ptr_to_addr(ptr);
>>
>>       spin_lock_irqsave(&pcpu_lock, flags);
>>
>
> Hmm, you need to call kmemleak_alloc() for each chunk allocated per
> possible cpu.
>
> Here is the (untested) patch for the allocation phase, need the same at
> freeing time
>
> diff --git a/mm/percpu-km.c b/mm/percpu-km.c
> index 89633fe..5061ac5 100644
> --- a/mm/percpu-km.c
> +++ b/mm/percpu-km.c
> @@ -37,9 +37,12 @@ static int pcpu_populate_chunk(struct pcpu_chunk *chunk, int off, int size)
>  {
>        unsigned int cpu;
>
> -       for_each_possible_cpu(cpu)
> -               memset((void *)pcpu_chunk_addr(chunk, cpu, 0) + off, 0, size);
> +       for_each_possible_cpu(cpu) {
> +               void *chunk_addr = (void *)pcpu_chunk_addr(chunk, cpu, 0) + off;
>
> +               kmemleak_alloc(chunk_addr, size, 1, GFP_KERNEL);
> +               memset(chunk_addr, 0, size);
> +       }
>        return 0;
>  }
>
> diff --git a/mm/percpu-vm.c b/mm/percpu-vm.c
> index ea53496..0d397cc 100644
> --- a/mm/percpu-vm.c
> +++ b/mm/percpu-vm.c
> @@ -342,8 +342,12 @@ static int pcpu_populate_chunk(struct pcpu_chunk *chunk, int off, int size)
>        /* commit new bitmap */
>        bitmap_copy(chunk->populated, populated, pcpu_unit_pages);
>  clear:
> -       for_each_possible_cpu(cpu)
> -               memset((void *)pcpu_chunk_addr(chunk, cpu, 0) + off, 0, size);
> +       for_each_possible_cpu(cpu) {
> +               void *chunk_addr = (void *)pcpu_chunk_addr(chunk, cpu, 0) + off;
> +
> +               kmemleak_alloc(chunk_addr, size, 1, GFP_KERNEL);
> +               memset(chunk_addr, 0, size);
> +       }
>        return 0;
>
>  err_unmap:
>
>

About this one, memory leak detector disabled(actually I enable it
while config the kernel) while booting system, and and found following
info in dmesg:
---------------------------------------------------------------------------------------------------------------
[ 0.370000] smpboot cpu 1: start_ip = 9a000
[ 0.010000] numa_add_cpu cpu 1 node 0: mask now 0-1
[ 0.530124] NMI watchdog enabled, takes one hw-pmu counter.
[ 0.530344] Brought up 2 CPUs
[ 0.530348] Total of 2 processors activated (10639.45 BogoMIPS).
[ 0.533083] kmemleak: Cannot insert 0xffff88007a3d7448 into the
object search tree (already existing)
[ 0.533083] Pid: 1, comm: swapper Tainted: G I 3.1.0-rc7+ #25
[ 0.533083] Call Trace:
[ 0.533083] [<ffffffff81256512>] create_object+0x2c2/0x360
[ 0.533083] [<ffffffff81920c5e>] kmemleak_alloc+0x7e/0x110
[ 0.533083] [<ffffffff811fd8cd>] pcpu_alloc+0xd2d/0x10f0
[ 0.533083] [<ffffffff81243129>] ? __kmalloc_track_caller+0x139/0x310
[ 0.533083] [<ffffffff811fdca8>] __alloc_percpu+0x18/0x30
[ 0.533083] [<ffffffff8128dded>] alloc_vfsmnt+0x11d/0x250
[ 0.533083] [<ffffffff8128dfd6>] vfs_kern_mount+0x46/0x130
[ 0.533083] [<ffffffff8194a283>] ? _raw_write_unlock+0x43/0x60
[ 0.533083] [<ffffffff82117cec>] shmem_init+0xb9/0x13b
[ 0.533083] [<ffffffff820ea2c6>] kernel_init+0x10e/0x23a
[ 0.533083] [<ffffffff8195a484>] kernel_thread_helper+0x4/0x10
[ 0.533083] [<ffffffff8194ac20>] ? _raw_spin_unlock_irq+0x50/0x80
[ 0.533083] [<ffffffff8194b834>] ? retint_restore_args+0x13/0x13
[ 0.533083] [<ffffffff820ea1b8>] ? start_kernel+0x6ce/0x6ce
[ 0.533083] [<ffffffff8195a480>] ? gs_change+0x13/0x13
[ 0.533083] kmemleak: Kernel memory leak detector disabled
[ 0.533083] kmemleak: Object 0xffff88007a200000 (size 1949696):
[ 0.533083] kmemleak: comm "swapper", pid 0, jiffies 4294937296
[ 0.533083] kmemleak: min_count = 0
[ 0.533083] kmemleak: count = 0
[ 0.533083] kmemleak: flags = 0x1
[ 0.533083] kmemleak: checksum = 0
[ 0.533083] kmemleak: backtrace:
[ 0.533083] [<ffffffff81256394>] create_object+0x144/0x360
[ 0.533083] [<ffffffff819214c8>] kmemleak_free_part+0x138/0x1d0
[ 0.533083] [<ffffffff8211e4e8>] kmemleak_init+0x30b/0x3fd
[ 0.533083] [<ffffffff820ea01c>] start_kernel+0x532/0x6ce
[ 0.533083] [<ffffffff820e938d>] x86_64_start_reservations+0x178/0x183
[ 0.533083] [<ffffffff820e94fb>] x86_64_start_kernel+0x163/0x179
[ 0.533083] [<ffffffffffffffff>] 0xffffffffffffffff
[ 0.533083] devtmpfs: initialized
[ 0.533083] gcov: version magic: 0x3430352a
[ 0.533083] PM: Registering ACPI NVS region at 7d2afe00 (8352 bytes)
[ 0.533083] print_constraints: dummy:
[ 0.533083] RTC time: 12:40:24, date: 09/27/11
[ 0.533083] NET: Registered protocol family 16
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