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Fix a race in the user-callchains code.

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Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Merge tag 'perf-urgent-2026-02-01' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull perf events fix from Ingo Molnar:
 "Fix a race in the user-callchains code"

* tag 'perf-urgent-2026-02-01' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  perf: sched: Fix perf crash with new is_user_task() helper
This commit is contained in:
Linus Torvalds 2026-02-01 10:47:21 -08:00
commit c00a879164
3 changed files with 9 additions and 4 deletions
Download patch file Download diff file Expand all files Collapse all files

5
include/linux/sched.h
View file

@ -1776,6 +1776,11 @@ static __always_inline bool is_percpu_thread(void)
(current->nr_cpus_allowed == 1);
}
static __always_inline bool is_user_task(struct task_struct *task)
{
return task->mm && !(task->flags & (PF_KTHREAD | PF_USER_WORKER));
}
/* Per-process atomic flags. */
#define PFA_NO_NEW_PRIVS 0 /* May not gain new privileges. */
#define PFA_SPREAD_PAGE 1 /* Spread page cache over cpuset */

2
kernel/events/callchain.c
View file

@ -246,7 +246,7 @@ get_perf_callchain(struct pt_regs *regs, bool kernel, bool user,
if (user && !crosstask) {
if (!user_mode(regs)) {
if (current->flags & (PF_KTHREAD | PF_USER_WORKER))
if (!is_user_task(current))
goto exit_put;
regs = task_pt_regs(current);
}

6
kernel/events/core.c
View file

@ -7460,7 +7460,7 @@ static void perf_sample_regs_user(struct perf_regs *regs_user,
if (user_mode(regs)) {
regs_user->abi = perf_reg_abi(current);
regs_user->regs = regs;
} else if (!(current->flags & (PF_KTHREAD | PF_USER_WORKER))) {
} else if (is_user_task(current)) {
perf_get_regs_user(regs_user, regs);
} else {
regs_user->abi = PERF_SAMPLE_REGS_ABI_NONE;
@ -8100,7 +8100,7 @@ static u64 perf_virt_to_phys(u64 virt)
* Try IRQ-safe get_user_page_fast_only first.
* If failed, leave phys_addr as 0.
*/
if (!(current->flags & (PF_KTHREAD | PF_USER_WORKER))) {
if (is_user_task(current)) {
struct page *p;
pagefault_disable();
@ -8215,7 +8215,7 @@ perf_callchain(struct perf_event *event, struct pt_regs *regs)
{
bool kernel = !event->attr.exclude_callchain_kernel;
bool user = !event->attr.exclude_callchain_user &&
!(current->flags & (PF_KTHREAD | PF_USER_WORKER));
is_user_task(current);
/* Disallow cross-task user callchains. */
bool crosstask = event->ctx->task && event->ctx->task != current;
bool defer_user = IS_ENABLED(CONFIG_UNWIND_USER) && user &&