> There are various points in the oom killer where the kernel must
> determine whether to panic or not. It's better to extract this to a
> helper function to remove all the confusion as to its semantics.
>
> Also fix a call to dump_header() where tasklist_lock is not read-
> locked, as required.
>
> There's no functional change with this patch.
>
> Acked-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
> Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx>
> ---
> include/linux/oom.h | 1 +
> mm/oom_kill.c | 53 +++++++++++++++++++++++++++-----------------------
> 2 files changed, 30 insertions(+), 24 deletions(-)
>
> diff --git a/include/linux/oom.h b/include/linux/oom.h
> --- a/include/linux/oom.h
> +++ b/include/linux/oom.h
> @@ -22,6 +22,7 @@ enum oom_constraint {
> CONSTRAINT_NONE,
> CONSTRAINT_CPUSET,
> CONSTRAINT_MEMORY_POLICY,
> + CONSTRAINT_MEMCG,
> };
>
> extern int try_set_zone_oom(struct zonelist *zonelist, gfp_t gfp_flags);
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -505,17 +505,40 @@ static int oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
> return oom_kill_task(victim);
> }
>
> +/*
> + * Determines whether the kernel must panic because of the panic_on_oom sysctl.
> + */
> +static void check_panic_on_oom(enum oom_constraint constraint, gfp_t gfp_mask,
> + int order)
> +{
> + if (likely(!sysctl_panic_on_oom))
> + return;
> + if (sysctl_panic_on_oom != 2) {
> + /*
> + * panic_on_oom == 1 only affects CONSTRAINT_NONE, the kernel
> + * does not panic for cpuset, mempolicy, or memcg allocation
> + * failures.
> + */
> + if (constraint != CONSTRAINT_NONE)
> + return;
> + }
> + read_lock(&tasklist_lock);
> + dump_header(NULL, gfp_mask, order, NULL);
> + read_unlock(&tasklist_lock);
> + panic("Out of memory: %s panic_on_oom is enabled\n",
> + sysctl_panic_on_oom == 2 ? "compulsory" : "system-wide");
> +}
> +
> #ifdef CONFIG_CGROUP_MEM_RES_CTLR
> void mem_cgroup_out_of_memory(struct mem_cgroup *mem, gfp_t gfp_mask)
> {
> unsigned long points = 0;
> struct task_struct *p;
>
> - if (sysctl_panic_on_oom == 2)
> - panic("out of memory(memcg). panic_on_oom is selected.\n");
> + check_panic_on_oom(CONSTRAINT_MEMCG, gfp_mask, 0);
> read_lock(&tasklist_lock);
> retry:
> - p = select_bad_process(&points, mem, CONSTRAINT_NONE, NULL);
> + p = select_bad_process(&points, mem, CONSTRAINT_MEMCG, NULL);
> if (!p || PTR_ERR(p) == -1UL)
> goto out;
>
> @@ -616,8 +639,8 @@ retry:
>
> /* Found nothing?!?! Either we hang forever, or we panic. */
> if (!p) {
> - read_unlock(&tasklist_lock);
> dump_header(NULL, gfp_mask, order, NULL);
> + read_unlock(&tasklist_lock);
> panic("Out of memory and no killable processes...\n");
> }
>
> @@ -639,9 +662,7 @@ void pagefault_out_of_memory(void)
> /* Got some memory back in the last second. */
> return;
>
> - if (sysctl_panic_on_oom)
> - panic("out of memory from page fault. panic_on_oom is selected.\n");
> -
> + check_panic_on_oom(CONSTRAINT_NONE, 0, 0);
> read_lock(&tasklist_lock);
> /* unknown gfp_mask and order */
> __out_of_memory(0, 0, CONSTRAINT_NONE, NULL);
> @@ -688,29 +709,13 @@ void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask,
> return;
> }
>
> - if (sysctl_panic_on_oom == 2) {
> - dump_header(NULL, gfp_mask, order, NULL);
> - panic("out of memory. Compulsory panic_on_oom is selected.\n");
> - }
> -
> /*
> * Check if there were limitations on the allocation (only relevant for
> * NUMA) that may require different handling.
> */
> constraint = constrained_alloc(zonelist, gfp_mask, nodemask);
> + check_panic_on_oom(constraint, gfp_mask, order);
> read_lock(&tasklist_lock);
> - if (unlikely(sysctl_panic_on_oom)) {
> - /*
> - * panic_on_oom only affects CONSTRAINT_NONE, the kernel
> - * should not panic for cpuset or mempolicy induced memory
> - * failures.
> - */
> - if (constraint == CONSTRAINT_NONE) {
> - dump_header(NULL, gfp_mask, order, NULL);
> - read_unlock(&tasklist_lock);
> - panic("Out of memory: panic_on_oom is enabled\n");
> - }
> - }
> __out_of_memory(gfp_mask, order, constraint, nodemask);
> read_unlock(&tasklist_lock);
>
pulled.
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