Re: [PATCH 1/2] xfs: allow kmem_zalloc_greedy to fail

[Michal Hocko]

I've just realized that Darrick was not on the CC list. Let's add him.
I believe this patch should go in in the current cycle because
5d17a73a2ebe was merged in this merge window and it can be abused...

The other patch [1] is not that urgent.

[1] http://lkml.kernel.org/r/20170302154541.16155-2-mhocko@xxxxxxxxxx

On Thu 02-03-17 16:45:40, Michal Hocko wrote:
> From: Michal Hocko <mhocko@xxxxxxxx>
> 
> Even though kmem_zalloc_greedy is documented it might fail the current
> code doesn't really implement this properly and loops on the smallest
> allowed size for ever. This is a problem because vzalloc might fail
> permanently - we might run out of vmalloc space or since 5d17a73a2ebe
> ("vmalloc: back off when the current task is killed") when the current
> task is killed. The later one makes the failure scenario much more
> probable than it used to be because it makes vmalloc() failures
> permanent for tasks with fatal signals pending.. Fix this by bailing out
> if the minimum size request failed.
> 
> This has been noticed by a hung generic/269 xfstest by Xiong Zhou.
> 
> fsstress: vmalloc: allocation failure, allocated 12288 of 20480 bytes, mode:0x14080c2(GFP_KERNEL|__GFP_HIGHMEM|__GFP_ZERO), nodemask=(null)
> fsstress cpuset=/ mems_allowed=0-1
> CPU: 1 PID: 23460 Comm: fsstress Not tainted 4.10.0-master-45554b2+ #21
> Hardware name: HP ProLiant DL380 Gen9/ProLiant DL380 Gen9, BIOS P89 10/05/2016
> Call Trace:
>  dump_stack+0x63/0x87
>  warn_alloc+0x114/0x1c0
>  ? alloc_pages_current+0x88/0x120
>  __vmalloc_node_range+0x250/0x2a0
>  ? kmem_zalloc_greedy+0x2b/0x40 [xfs]
>  ? free_hot_cold_page+0x21f/0x280
>  vzalloc+0x54/0x60
>  ? kmem_zalloc_greedy+0x2b/0x40 [xfs]
>  kmem_zalloc_greedy+0x2b/0x40 [xfs]
>  xfs_bulkstat+0x11b/0x730 [xfs]
>  ? xfs_bulkstat_one_int+0x340/0x340 [xfs]
>  ? selinux_capable+0x20/0x30
>  ? security_capable+0x48/0x60
>  xfs_ioc_bulkstat+0xe4/0x190 [xfs]
>  xfs_file_ioctl+0x9dd/0xad0 [xfs]
>  ? do_filp_open+0xa5/0x100
>  do_vfs_ioctl+0xa7/0x5e0
>  SyS_ioctl+0x79/0x90
>  do_syscall_64+0x67/0x180
>  entry_SYSCALL64_slow_path+0x25/0x25
> 
> fsstress keeps looping inside kmem_zalloc_greedy without any way out
> because vmalloc keeps failing due to fatal_signal_pending.
> 
> Reported-by: Xiong Zhou <xzhou@xxxxxxxxxx>
> Analyzed-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
> ---
>  fs/xfs/kmem.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/fs/xfs/kmem.c b/fs/xfs/kmem.c
> index 339c696bbc01..ee95f5c6db45 100644
> --- a/fs/xfs/kmem.c
> +++ b/fs/xfs/kmem.c
> @@ -34,6 +34,8 @@ kmem_zalloc_greedy(size_t *size, size_t minsize, size_t maxsize)
>  	size_t		kmsize = maxsize;
>  
>  	while (!(ptr = vzalloc(kmsize))) {
> +		if (kmsize == minsize)
> +			break;
>  		if ((kmsize >>= 1) <= minsize)
>  			kmsize = minsize;
>  	}
> -- 
> 2.11.0
> 

-- 
Michal Hocko
SUSE Labs