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

[Michal Hocko]

On Sat 04-03-17 09:54:44, Dave Chinner wrote:
> On Thu, Mar 02, 2017 at 04:45:40PM +0100, 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;
> >  	}
> 
> Seems wrong to me - this function used to have lots of callers and
> over time we've slowly removed them or replaced them with something
> else. I'd suggest removing it completely, replacing the call sites
> with kmem_zalloc_large().

I do not really care how this gets fixed. Dropping kmem_zalloc_greedy
sounds like a way to go. I am not familiar with xfs_bulkstat to do an
edicated guess which allocation size to use. So I guess I have to
postpone this to you guys if you prefer that route though.

Thanks!
-- 
Michal Hocko
SUSE Labs