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

[Michal Hocko]

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