[PATCH] fs: fix for core dumping of a process getting oom-killed

From: Vishnu Rangayyan
Date: Tue Sep 21 2021 - 02:41:36 EST

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Processes inside a memcg that get core dumped when there is less memory
available in the memcg can have the core dumping interrupted by the oom-killer.
We saw this with qemu processes inside a memcg, as in this trace below.
The memcg was not out of memory when the core dump was triggered.

[201169.028782] qemu-kata-syste invoked oom-killer: gfp_mask=0x101c4a(GFP_NOFS|__GFP_HIGHMEM|__GFP_HARDWALL|__GFP_MOVABLE|__GFP_WRITE), order=0, oom_score_adj=-100
[201169.028785] CPU: 3 PID: 1887079 Comm: qemu-kata-syste Kdump: loaded Tainted: P W O 5.4.77-7.el7pie #1
[201169.028786] Call Trace:
[201169.028794] dump_stack+0x8f/0xd0
[201169.028797] dump_header+0x4a/0x1d8
[201169.028799] oom_kill_process.cold.33+0xb/0x10
[201169.028800] out_of_memory+0x199/0x460
[201169.028804] mem_cgroup_out_of_memory+0xbe/0xd0
[201169.028805] try_charge+0x789/0x800
[201169.028807] mem_cgroup_try_charge+0x6a/0x190
[201169.028809] __add_to_page_cache_locked+0x29d/0x2f0
[201169.028812] ? scan_shadow_nodes+0x30/0x30
[201169.028813] add_to_page_cache_lru+0x4a/0xc0
[201169.028814] pagecache_get_page+0x101/0x220
[201169.028816] grab_cache_page_write_begin+0x1f/0x40
[201169.028818] iomap_write_begin.constprop.31+0x1b6/0x330
[201169.028819] ? iomap_write_end+0x240/0x240
[201169.028822] ? xfs_file_iomap_begin+0x387/0x5d0
[201169.028823] ? iomap_write_end+0x240/0x240
[201169.028824] iomap_write_actor+0x92/0x170
[201169.028825] ? iomap_write_end+0x240/0x240
[201169.028826] iomap_apply+0xba/0x130
[201169.028827] ? iomap_write_end+0x240/0x240
[201169.028828] iomap_file_buffered_write+0x61/0x80
[201169.028829] ? iomap_write_end+0x240/0x240
[201169.028831] xfs_file_buffered_aio_write+0xca/0x320
[201169.028832] new_sync_write+0x11b/0x1b0
[201169.028833] __kernel_write+0x4f/0xf0
[201169.028834] dump_emit+0x91/0xc0
[201169.028837] elf_core_dump+0x818/0x9a0
[201169.028839] do_coredump+0x52b/0xb0b
[201169.028842] get_signal+0x134/0x820
[201169.028844] do_signal+0x36/0x5d0
[201169.028845] ? do_send_specific+0x66/0x80
[201169.028847] ? audit_filter_inodes+0x2e/0x100
[201169.028848] ? audit_filter_syscall.constprop.19+0x2c/0xd0
[201169.028850] do_syscall_64+0x1aa/0x58e
[201169.028852] ? trace_hardirqs_off_thunk+0x1a/0x30
[201169.028854] entry_SYSCALL_64_after_hwframe+0x49/0xbe
[201169.028856] RIP: 0033:0x7fdf0bbd73d7
[201169.028857] Code: 02 00 00 85 f6 75 34 b8 ba 00 00 00 0f 05 89 c1 64 89 04 25 d0 02 00 00 89 c6 48 63 d7 48 63 f6 48 63 f9 b8 ea 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 1e f3 c3 0f 1f 80 00 00 00 00 85 c9 7f db 89
[201169.028858] RSP: 002b:00007fff9b56a018 EFLAGS: 00000202 ORIG_RAX: 00000000000000ea
[201169.028860] RAX: 0000000000000000 RBX: 00007fdf20d7b000 RCX: 00007fdf0bbd73d7
[201169.028860] RDX: 0000000000000006 RSI: 00000000001ccb67 RDI: 00000000001ccb67
[201169.028861] RBP: 00007fdf0bd2be00 R08: 0000000000000000 R09: 0000556728a30390
[201169.028861] R10: 0000000000000008 R11: 0000000000000202 R12: 0000556727115cb5
[201169.028862] R13: 0000556727115e20 R14: 00005567277fe700 R15: 0000556727806701
[201169.028863] memory: usage 12218368kB, limit 12218368kB, failcnt 1728013
[201169.028864] memory+swap: usage 12218368kB, limit 9007199254740988kB, failcnt 0
[201169.028864] kmem: usage 154424kB, limit 9007199254740988kB, failcnt 0
[201169.028880] oom-kill:constraint=CONSTRAINT_MEMCG,nodemask=(null),cpuset=podacfa3d53-2068-4b61-a754-fa21968b4201,mems_allowed=0-1,oom_memcg=/kubepods/burstable/podacfa3d53-2068-4b61-a754-fa21968b4201,task_memcg=/kubepods/burstable/podacfa3d53-2068-4b61-a754-fa21968b4201,task=qemu-kata-syste,pid=1887079,uid=0
[201169.028888] Memory cgroup out of memory: Killed process 1887079 (qemu-kata-syste) total-vm:13598556kB, anon-rss:39836kB, file-rss:8712kB, shmem-rss:12017992kB, UID:0 pgtables:24204kB oom_score_adj:-100
[201169.045201] oom_reaper: reaped process 1887079 (qemu-kata-syste), now anon-rss:0kB, file-rss:28kB, shmem-rss:12018016kB

This change adds an fsync only for regular file core dumps based on a configurable limit core_sync_bytes placed alongside other core dump params and defaults the limit to (an arbitrary value) of 128KB.
Setting core_sync_bytes to zero disables the sync.

Cc: stable@xxxxxxxxxxxxxxx
Reported-by: Eric Ernst <eric_ernst@xxxxxxxxx>
Signed-off-by: Vishnu Rangayyan <vrangayyan@xxxxxxxxx>
---
fs/coredump.c | 9 +++++++++
include/linux/binfmts.h | 1 +
include/linux/coredump.h | 1 +
kernel/sysctl.c | 7 +++++++
4 files changed, 18 insertions(+)

diff --git a/fs/coredump.c b/fs/coredump.c
index 3224dee44d30..187813704533 100644
--- a/fs/coredump.c
+++ b/fs/coredump.c
@@ -54,6 +54,7 @@

int core_uses_pid;
unsigned int core_pipe_limit;
+unsigned int core_sync_bytes = 131072; /* sync core file every so many bytes */
char core_pattern[CORENAME_MAX_SIZE] = "core";
static int core_name_size = CORENAME_MAX_SIZE;

@@ -866,6 +867,14 @@ static int __dump_emit(struct coredump_params *cprm, const void *addr, int nr)
n = __kernel_write(file, addr, nr, &pos);
if (n != nr)
return 0;
+ if (file->f_inode && S_ISREG(file->f_inode->i_mode)) {
+ cprm->not_synced += n;
+ if (cprm->not_synced >= core_sync_bytes &&
+ core_sync_bytes) {
+ generic_file_fsync(file, 0, pos - 1, 0);
+ cprm->not_synced = 0;
+ }
+ }
file->f_pos = pos;
cprm->written += n;
cprm->pos += n;
diff --git a/include/linux/binfmts.h b/include/linux/binfmts.h
index 049cf9421d83..588d8f240715 100644
--- a/include/linux/binfmts.h
+++ b/include/linux/binfmts.h
@@ -84,6 +84,7 @@ struct coredump_params {
struct file *file;
unsigned long limit;
unsigned long mm_flags;
+ loff_t not_synced;
loff_t written;
loff_t pos;
loff_t to_skip;
diff --git a/include/linux/coredump.h b/include/linux/coredump.h
index 78fcd776b185..2f65e2f10118 100644
--- a/include/linux/coredump.h
+++ b/include/linux/coredump.h
@@ -17,6 +17,7 @@ struct core_vma_metadata {
extern int core_uses_pid;
extern char core_pattern[];
extern unsigned int core_pipe_limit;
+extern unsigned int core_sync_bytes;

/*
* These are the only things you should do on a core-file: use only these
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 083be6af29d7..89b54e9ca963 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1948,6 +1948,13 @@ static struct ctl_table kern_table[] = {
.mode = 0644,
.proc_handler = proc_dointvec,
},
+ {
+ .procname = "core_sync_bytes",
+ .data = &core_sync_bytes,
+ .maxlen = sizeof(unsigned int),
+ .mode = 0644,
+ .proc_handler = proc_dointvec,
+ },
#endif
#ifdef CONFIG_PROC_SYSCTL
{
--
2.25.1

Next message: Huang, Ying: "Re: [PATCH] mm/migrate: fix CPUHP state to update node demotion order"
Previous message: Masanari Iida: "[PATCH] Doc: networking: Fox a typo in ice.rst"
Next in thread: Greg Kroah-Hartman: "Re: [PATCH] fs: fix for core dumping of a process getting oom-killed"
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