On 02/09/2015 10:48 PM, Stefan Hajnoczi wrote: > On Mon, Feb 09, 2015 at 02:50:39PM +0800, Bin Wu wrote: >> From: Bin Wu <wu.wu...@huawei.com> >> >> We tested VMs migration with their disk images by drive_mirror. With >> migration, two VMs copyed large files between each other. During the >> test, a segfault occured. The stack was as follow: >> >> (gdb) bt >> qemu-coroutine-lock.c:66 >> to=0x7fa5a1798648) at qemu-coroutine.c:97 >> request=0x7fa28c2ffa10, reply=0x7fa28c2ffa30, qiov=0x0, offset=0) at >> block/nbd-client.c:165 >> sector_num=8552704, nb_sectors=2040, qiov=0x7fa5a1757468, offset=0) at >> block/nbd-client.c:262 >> sector_num=8552704, nb_sectors=2048, qiov=0x7fa5a1757468) at >> block/nbd-client.c:296 >> nb_sectors=2048, qiov=0x7fa5a1757468) at block/nbd.c:291 >> req=0x7fa28c2ffbb0, offset=4378984448, bytes=1048576, qiov=0x7fa5a1757468, >> flags=0) at block.c:3321 >> offset=4378984448, bytes=1048576, qiov=0x7fa5a1757468, flags=(unknown: 0)) at >> block.c:3447 >> sector_num=8552704, nb_sectors=2048, qiov=0x7fa5a1757468, flags=(unknown: >> 0)) at >> block.c:3471 >> nb_sectors=2048, qiov=0x7fa5a1757468) at block.c:3480 >> nb_sectors=2048, qiov=0x7fa5a1757468) at block/raw_bsd.c:62 >> req=0x7fa28c2ffe30, offset=4378984448, bytes=1048576, qiov=0x7fa5a1757468, >> flags=0) at block.c:3321 >> offset=4378984448, bytes=1048576, qiov=0x7fa5a1757468, flags=(unknown: 0)) at >> block.c:3447 >> sector_num=8552704, nb_sectors=2048, qiov=0x7fa5a1757468, flags=(unknown: >> 0)) at >> block.c:3471 >> coroutine-ucontext.c:121 > > This backtrace is incomplete. Where are the function names? The > parameter lists appear incomplete too. > >> After analyzing the stack and reviewing the code, we find the >> qemu_co_queue_run_restart should not be put in the coroutine_swap function >> which >> can be invoked by qemu_coroutine_enter or qemu_coroutine_yield. Only >> qemu_coroutine_enter needs to restart the co_queue. >> >> The error scenario is as follow: coroutine C1 enters C2, C2 yields >> back to C1, then C1 ternimates and the related coroutine memory >> becomes invalid. After a while, the C2 coroutine is entered again. >> At this point, C1 is used as a parameter passed to >> qemu_co_queue_run_restart. Therefore, qemu_co_queue_run_restart >> accesses an invalid memory and a segfault error ocurrs. >> >> The qemu_co_queue_run_restart function re-enters coroutines waiting >> in the co_queue. However, this function should be only used int the >> qemu_coroutine_enter context. Only in this context, when the current >> coroutine gets execution control again(after the execution of >> qemu_coroutine_switch), we can restart the target coutine because the >> target coutine has yielded back to the current coroutine or it has >> terminated. >> >> First we want to put qemu_co_queue_run_restart in qemu_coroutine_enter, >> but we find we can not access the target coroutine if it terminates. > > This example captures the scenario you describe: > > diff --git a/qemu-coroutine.c b/qemu-coroutine.c > index 525247b..883cbf5 100644 > --- a/qemu-coroutine.c > +++ b/qemu-coroutine.c > @@ -103,7 +103,10 @@ static void coroutine_swap(Coroutine *from, Coroutine > *to) > { > CoroutineAction ret; > > + fprintf(stderr, "> %s from %p to %p\n", __func__, from, to); > ret = qemu_coroutine_switch(from, to, COROUTINE_YIELD); > + fprintf(stderr, "< %s from %p to %p switch %s\n", __func__, from, to, > + ret == COROUTINE_YIELD ? "yield" : "terminate"); > > qemu_co_queue_run_restart(to); > > @@ -111,6 +114,7 @@ static void coroutine_swap(Coroutine *from, Coroutine *to) > case COROUTINE_YIELD: > return; > case COROUTINE_TERMINATE: > + fprintf(stderr, "coroutine_delete %p\n", to); > trace_qemu_coroutine_terminate(to); > coroutine_delete(to); > return; > diff --git a/tests/test-coroutine.c b/tests/test-coroutine.c > index 27d1b6f..d44c428 100644 > --- a/tests/test-coroutine.c > +++ b/tests/test-coroutine.c > @@ -13,6 +13,7 @@ > > #include <glib.h> > #include "block/coroutine.h" > +#include "block/coroutine_int.h" > > /* > * Check that qemu_in_coroutine() works > @@ -122,6 +123,35 @@ static void test_yield(void) > g_assert_cmpint(i, ==, 5); /* coroutine must yield 5 times */ > } > > +static void coroutine_fn c2_fn(void *opaque) > +{ > + fprintf(stderr, "c2 Part 1\n"); > + qemu_coroutine_yield(); > + fprintf(stderr, "c2 Part 2\n"); > +} > + > +static void coroutine_fn c1_fn(void *opaque) > +{ > + Coroutine *c2 = opaque; > + > + fprintf(stderr, "c1 Part 1\n"); > + qemu_coroutine_enter(c2, NULL); > + fprintf(stderr, "c1 Part 2\n"); > +} > + > +static void test_co_queue(void) > +{ > + Coroutine *c1; > + Coroutine *c2; > + > + c1 = qemu_coroutine_create(c1_fn); > + c2 = qemu_coroutine_create(c2_fn); > + > + qemu_coroutine_enter(c1, c2); > + memset(c1, 0xff, sizeof(Coroutine)); > + qemu_coroutine_enter(c2, NULL); > +} > + > /* > * Check that creation, enter, and return work > */ > @@ -343,6 +373,7 @@ static void perf_cost(void) > int main(int argc, char **argv) > { > g_test_init(&argc, &argv, NULL); > + g_test_add_func("/basic/co_queue", test_co_queue); > g_test_add_func("/basic/lifecycle", test_lifecycle); > g_test_add_func("/basic/yield", test_yield); > g_test_add_func("/basic/nesting", test_nesting); > > Here is the output (with printfs in coroutine_swap): > > -> coroutine_swap from MAIN to C1 > c1 Part 1 > -> coroutine_swap from C1 to C2 > c2 Part 1 > -> coroutine_swap from C2 to C1 > <- coroutine_swap from C1 to C2 switch yield > c1 Part 2 > <- coroutine_swap from MAIN to C1 switch terminate > coroutine_delete C1 > -> coroutine_swap from MAIN to C2 > <- coroutine_swap from C2 to C1 switch yield !!! > c2 Part 2 > <- coroutine_swap from MAIN to C2 switch terminate > coroutine_delete C2 > > I have marked the problematic line with "!!!". The to=C1 variable is > used after C1 has been deleted.
How to build the test program? make test? I meet the following errors: make test make -C tests/tcg test make[1]: Entering directory '/work/src/qemu/tests/tcg' CC test_path.o In file included from /work/src/qemu/include/qemu-common.h:43:0, from /work/src/qemu/util/cutils.c:24, from test_path.c:3: /work/src/qemu/include/glib-compat.h:19:18: fatal error: glib.h: No such file or directory #include <glib.h> ^ compilation terminated. /work/src/qemu/rules.mak:57: recipe for target 'test_path.o' failed make[1]: *** [test_path.o] Error 1 make[1]: Leaving directory '/work/src/qemu/tests/tcg' Makefile:428: recipe for target 'test' failed make: *** [test] Error 2 Do I miss something? Thanks Wen Congyang > > The test crashes since it writes 0xff to C1 after it has terminated. > >> Signed-off-by: Bin Wu <wu.wu...@huawei.com> >> --- >> qemu-coroutine.c | 16 ++++++++++------ >> 1 file changed, 10 insertions(+), 6 deletions(-) >> >> diff --git a/qemu-coroutine.c b/qemu-coroutine.c >> index 525247b..cc0bdfa 100644 >> --- a/qemu-coroutine.c >> +++ b/qemu-coroutine.c >> @@ -99,29 +99,31 @@ static void coroutine_delete(Coroutine *co) >> qemu_coroutine_delete(co); >> } >> >> -static void coroutine_swap(Coroutine *from, Coroutine *to) >> +static CoroutineAction coroutine_swap(Coroutine *from, Coroutine *to) >> { >> CoroutineAction ret; >> >> ret = qemu_coroutine_switch(from, to, COROUTINE_YIELD); >> >> - qemu_co_queue_run_restart(to); >> - >> switch (ret) { >> case COROUTINE_YIELD: >> - return; >> + break; >> case COROUTINE_TERMINATE: >> trace_qemu_coroutine_terminate(to); >> + qemu_co_queue_run_restart(to); >> coroutine_delete(to); >> - return; >> + break; >> default: >> abort(); >> } >> + >> + return ret; >> } >> >> void qemu_coroutine_enter(Coroutine *co, void *opaque) >> { >> Coroutine *self = qemu_coroutine_self(); >> + CoroutineAction ret; >> >> trace_qemu_coroutine_enter(self, co, opaque); >> >> @@ -132,7 +134,9 @@ void qemu_coroutine_enter(Coroutine *co, void *opaque) >> >> co->caller = self; >> co->entry_arg = opaque; >> - coroutine_swap(self, co); >> + ret = coroutine_swap(self, co); >> + if (ret == COROUTINE_YIELD) >> + qemu_co_queue_run_restart(co); >> } > > Your fix looks correct although QEMU coding style requires {}. > > I tried to think of a simpler solution that keeps a single > qemu_co_queue_run_restart() call but was unable to find one. > > Please send another revision with a test-coroutine.c test case so we can > protect against regressions. > > Thanks, > Stefan >