| Message ID | 20230213125238.331881-3-iii@linux.ibm.com |
|---|---|
| State | New |
| Headers | show |
| Series | Fix deadlock when dying because of a signal | expand |
On 2/13/23 02:52, Ilya Leoshkevich wrote: > Currently dying to one of the core_dump_signal()s deadlocks, because > dump_core_and_abort() calls start_exclusive() two times: first via > stop_all_tasks(), and then via preexit_cleanup() -> > qemu_plugin_user_exit(). > > There are a number of ways to solve this: resume after dumping core; > check cpu_in_exclusive_context() in qemu_plugin_user_exit(); or make > {start,end}_exclusive() recursive. Pick the last option, since it's > the most straightforward one. > > Fixes: da91c1920242 ("linux-user: Clean up when exiting due to a signal") > Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com> > --- > cpus-common.c | 12 ++++++++++-- > include/hw/core/cpu.h | 4 ++-- > 2 files changed, 12 insertions(+), 4 deletions(-) > > diff --git a/cpus-common.c b/cpus-common.c > index 793364dc0ed..a0c52cd187f 100644 > --- a/cpus-common.c > +++ b/cpus-common.c > @@ -192,6 +192,11 @@ void start_exclusive(void) > CPUState *other_cpu; > int running_cpus; > > + if (current_cpu->exclusive_context_count) { > + current_cpu->exclusive_context_count++; > + return; > + } > + > qemu_mutex_lock(&qemu_cpu_list_lock); > exclusive_idle(); > > @@ -219,13 +224,16 @@ void start_exclusive(void) > */ > qemu_mutex_unlock(&qemu_cpu_list_lock); > > - current_cpu->in_exclusive_context = true; > + current_cpu->exclusive_context_count++; I think this line would be clearer as "= 1". Otherwise, Reviewed-by: Richard Henderson <richard.henderson@linaro.org> r~
Ilya Leoshkevich <iii@linux.ibm.com> writes: > Currently dying to one of the core_dump_signal()s deadlocks, because > dump_core_and_abort() calls start_exclusive() two times: first via > stop_all_tasks(), and then via preexit_cleanup() -> > qemu_plugin_user_exit(). > > There are a number of ways to solve this: resume after dumping core; > check cpu_in_exclusive_context() in qemu_plugin_user_exit(); or make > {start,end}_exclusive() recursive. Pick the last option, since it's > the most straightforward one. > > Fixes: da91c1920242 ("linux-user: Clean up when exiting due to a signal") > Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com> Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
diff --git a/cpus-common.c b/cpus-common.c index 793364dc0ed..a0c52cd187f 100644 --- a/cpus-common.c +++ b/cpus-common.c @@ -192,6 +192,11 @@ void start_exclusive(void) CPUState *other_cpu; int running_cpus; + if (current_cpu->exclusive_context_count) { + current_cpu->exclusive_context_count++; + return; + } + qemu_mutex_lock(&qemu_cpu_list_lock); exclusive_idle(); @@ -219,13 +224,16 @@ void start_exclusive(void) */ qemu_mutex_unlock(&qemu_cpu_list_lock); - current_cpu->in_exclusive_context = true; + current_cpu->exclusive_context_count++; } /* Finish an exclusive operation. */ void end_exclusive(void) { - current_cpu->in_exclusive_context = false; + current_cpu->exclusive_context_count--; + if (current_cpu->exclusive_context_count) { + return; + } qemu_mutex_lock(&qemu_cpu_list_lock); qatomic_set(&pending_cpus, 0); diff --git a/include/hw/core/cpu.h b/include/hw/core/cpu.h index 2417597236b..671f041bec6 100644 --- a/include/hw/core/cpu.h +++ b/include/hw/core/cpu.h @@ -349,7 +349,7 @@ struct CPUState { bool unplug; bool crash_occurred; bool exit_request; - bool in_exclusive_context; + int exclusive_context_count; uint32_t cflags_next_tb; /* updates protected by BQL */ uint32_t interrupt_request; @@ -758,7 +758,7 @@ void async_safe_run_on_cpu(CPUState *cpu, run_on_cpu_func func, run_on_cpu_data */ static inline bool cpu_in_exclusive_context(const CPUState *cpu) { - return cpu->in_exclusive_context; + return cpu->exclusive_context_count; } /**
Currently dying to one of the core_dump_signal()s deadlocks, because dump_core_and_abort() calls start_exclusive() two times: first via stop_all_tasks(), and then via preexit_cleanup() -> qemu_plugin_user_exit(). There are a number of ways to solve this: resume after dumping core; check cpu_in_exclusive_context() in qemu_plugin_user_exit(); or make {start,end}_exclusive() recursive. Pick the last option, since it's the most straightforward one. Fixes: da91c1920242 ("linux-user: Clean up when exiting due to a signal") Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com> --- cpus-common.c | 12 ++++++++++-- include/hw/core/cpu.h | 4 ++-- 2 files changed, 12 insertions(+), 4 deletions(-)