[PATCH] mm/oom: added option 'oom_dump_task_cmdline'

[Stepan Bujnak <stepan@pex.com>]

When oom_dump_tasks is enabled, this option will try to display task
cmdline instead of the command name in the system-wide task dump.

This is useful in some cases e.g. on postgres server. If OOM killer is
invoked it will show a bunch of tasks called 'postgres'. With this
option enabled it will show additional information like the database
user, database name and what it is currently doing.

Other example is python. Instead of just 'python' it will also show the
script name currently being executed.

Signed-off-by: Stepan Bujnak <stepan@pex.com>
---
 Documentation/sysctl/vm.txt | 10 ++++++++++
 include/linux/oom.h         |  1 +
 kernel/sysctl.c             |  7 +++++++
 mm/oom_kill.c               | 20 ++++++++++++++++++--
 4 files changed, 36 insertions(+), 2 deletions(-)

diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt
index 187ce4f599a2..74278c8c30d2 100644
--- a/Documentation/sysctl/vm.txt
+++ b/Documentation/sysctl/vm.txt
@@ -50,6 +50,7 @@ Currently, these files are in /proc/sys/vm:
 - nr_trim_pages         (only if CONFIG_MMU=n)
 - numa_zonelist_order
 - oom_dump_tasks
+- oom_dump_task_cmdline
 - oom_kill_allocating_task
 - overcommit_kbytes
 - overcommit_memory
@@ -639,6 +640,15 @@ The default value is 1 (enabled).
 
 ==============================================================
 
+oom_dump_task_cmdline
+
+When oom_dump_tasks is enabled, this option will try to display task cmdline
+instead of the command name in the system-wide task dump.
+
+The default value is 0 (disabled).
+
+==============================================================
+
 oom_kill_allocating_task
 
 This enables or disables killing the OOM-triggering task in
diff --git a/include/linux/oom.h b/include/linux/oom.h
index d07992009265..461b15b3b695 100644
--- a/include/linux/oom.h
+++ b/include/linux/oom.h
@@ -125,6 +125,7 @@ extern struct task_struct *find_lock_task_mm(struct task_struct *p);
 
 /* sysctls */
 extern int sysctl_oom_dump_tasks;
+extern int sysctl_oom_dump_task_cmdline;
 extern int sysctl_oom_kill_allocating_task;
 extern int sysctl_panic_on_oom;
 #endif /* _INCLUDE_LINUX_OOM_H */
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index ba4d9e85feb8..4edc5f8e6cf9 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1288,6 +1288,13 @@ static struct ctl_table vm_table[] = {
 		.mode		= 0644,
 		.proc_handler	= proc_dointvec,
 	},
+	{
+		.procname	= "oom_dump_task_cmdline",
+		.data		= &sysctl_oom_dump_task_cmdline,
+		.maxlen		= sizeof(sysctl_oom_dump_task_cmdline),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec,
+	},
 	{
 		.procname	= "overcommit_ratio",
 		.data		= &sysctl_overcommit_ratio,
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 26ea8636758f..736fa0a6ab8d 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -41,6 +41,7 @@
 #include <linux/kthread.h>
 #include <linux/init.h>
 #include <linux/mmu_notifier.h>
+#include <linux/string_helpers.h>
 
 #include <asm/tlb.h>
 #include "internal.h"
@@ -52,6 +53,7 @@
 int sysctl_panic_on_oom;
 int sysctl_oom_kill_allocating_task;
 int sysctl_oom_dump_tasks = 1;
+int sysctl_oom_dump_task_cmdline;
 
 /*
  * Serializes oom killer invocations (out_of_memory()) from all contexts to
@@ -404,9 +406,18 @@ static void dump_tasks(struct mem_cgroup *memcg, const nodemask_t *nodemask)
 	pr_info("[  pid  ]   uid  tgid total_vm      rss pgtables_bytes swapents oom_score_adj name\n");
 	rcu_read_lock();
 	for_each_process(p) {
+		char *name, *cmd = NULL;
+
 		if (oom_unkillable_task(p, memcg, nodemask))
 			continue;
 
+		/*
+		 * This needs to be done before calling find_lock_task_mm()
+		 * since both grab a task lock which would result in deadlock.
+		 */
+		if (sysctl_oom_dump_task_cmdline)
+			cmd = kstrdup_quotable_cmdline(p, GFP_KERNEL);
+
 		task = find_lock_task_mm(p);
 		if (!task) {
 			/*
@@ -414,16 +425,21 @@ static void dump_tasks(struct mem_cgroup *memcg, const nodemask_t *nodemask)
 			 * detached their mm's.  There's no need to report
 			 * them; they can't be oom killed anyway.
 			 */
-			continue;
+			goto done;
 		}
 
+		name = cmd ? cmd : task->comm;
+
 		pr_info("[%7d] %5d %5d %8lu %8lu %8ld %8lu         %5hd %s\n",
 			task->pid, from_kuid(&init_user_ns, task_uid(task)),
 			task->tgid, task->mm->total_vm, get_mm_rss(task->mm),
 			mm_pgtables_bytes(task->mm),
 			get_mm_counter(task->mm, MM_SWAPENTS),
-			task->signal->oom_score_adj, task->comm);
+			task->signal->oom_score_adj, name);
 		task_unlock(task);
+
+done:
+		kfree(cmd);
 	}
 	rcu_read_unlock();
 }
-- 
2.17.1