diff options
| author | Benjamin Berg <benjamin.berg@intel.com> | 2025-03-14 14:08:15 +0100 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2025-05-02 07:59:19 +0200 |
| commit | da780c4a075ba2deb05ae29f0af4a990578c7901 (patch) | |
| tree | 99bbb582bb9d50bbf7f94730e1eee677ace9cec5 | |
| parent | 0a205fdbb388daafec587dc91c9526742f28fac9 (diff) | |
um: work around sched_yield not yielding in time-travel mode
[ Upstream commit 887c5c12e80c8424bd471122d2e8b6b462e12874 ]
sched_yield by a userspace may not actually cause scheduling in
time-travel mode as no time has passed. In the case seen it appears to
be a badly implemented userspace spinlock in ASAN. Unfortunately, with
time-travel it causes an extreme slowdown or even deadlock depending on
the kernel configuration (CONFIG_UML_MAX_USERSPACE_ITERATIONS).
Work around it by accounting time to the process whenever it executes a
sched_yield syscall.
Signed-off-by: Benjamin Berg <benjamin.berg@intel.com>
Link: https://patch.msgid.link/20250314130815.226872-1-benjamin@sipsolutions.net
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
| -rw-r--r-- | arch/um/include/linux/time-internal.h | 2 | ||||
| -rw-r--r-- | arch/um/kernel/skas/syscall.c | 11 |
2 files changed, 13 insertions, 0 deletions
diff --git a/arch/um/include/linux/time-internal.h b/arch/um/include/linux/time-internal.h index b22226634ff6..138908b999d7 100644 --- a/arch/um/include/linux/time-internal.h +++ b/arch/um/include/linux/time-internal.h @@ -83,6 +83,8 @@ extern void time_travel_not_configured(void); #define time_travel_del_event(...) time_travel_not_configured() #endif /* CONFIG_UML_TIME_TRAVEL_SUPPORT */ +extern unsigned long tt_extra_sched_jiffies; + /* * Without CONFIG_UML_TIME_TRAVEL_SUPPORT this is a linker error if used, * which is intentional since we really shouldn't link it in that case. diff --git a/arch/um/kernel/skas/syscall.c b/arch/um/kernel/skas/syscall.c index b09e85279d2b..a5beaea2967e 100644 --- a/arch/um/kernel/skas/syscall.c +++ b/arch/um/kernel/skas/syscall.c @@ -31,6 +31,17 @@ void handle_syscall(struct uml_pt_regs *r) goto out; syscall = UPT_SYSCALL_NR(r); + + /* + * If no time passes, then sched_yield may not actually yield, causing + * broken spinlock implementations in userspace (ASAN) to hang for long + * periods of time. + */ + if ((time_travel_mode == TT_MODE_INFCPU || + time_travel_mode == TT_MODE_EXTERNAL) && + syscall == __NR_sched_yield) + tt_extra_sched_jiffies += 1; + if (syscall >= 0 && syscall < __NR_syscalls) { unsigned long ret = EXECUTE_SYSCALL(syscall, regs); |