Commit 04d7e098 authored by Josh Stone's avatar Josh Stone Committed by Catalin Marinas

arm64: fix missing syscall trace exit

If a syscall is entered without TIF_SYSCALL_TRACE set, then it goes on
the fast path.  It's then possible to have TIF_SYSCALL_TRACE added in
the middle of the syscall, but ret_fast_syscall doesn't check this flag
again.  This causes a ptrace syscall-exit-stop to be missed.

For instance, from a PTRACE_EVENT_FORK reported during do_fork, the
tracer might resume with PTRACE_SYSCALL, setting TIF_SYSCALL_TRACE.
Now the completion of the fork should have a syscall-exit-stop.

Russell King fixed this on arm by re-checking _TIF_SYSCALL_WORK in the
fast exit path.  Do the same on arm64.
Reviewed-by: default avatarWill Deacon <>
Cc: Russell King <>
Signed-off-by: default avatarJosh Stone <>
Signed-off-by: default avatarCatalin Marinas <>
parent addc8120
......@@ -611,11 +611,16 @@ ENDPROC(cpu_switch_to)
disable_irq // disable interrupts
ldr x1, [tsk, #TI_FLAGS]
ldr x1, [tsk, #TI_FLAGS] // re-check for syscall tracing
and x2, x1, #_TIF_SYSCALL_WORK
cbnz x2, ret_fast_syscall_trace
and x2, x1, #_TIF_WORK_MASK
cbnz x2, fast_work_pending
enable_step_tsk x1, x2
kernel_exit 0, ret = 1
enable_irq // enable interrupts
b __sys_trace_return
* Ok, we need to do extra processing, enter the slow path.
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