| Message ID | 20170601160847.23720-1-roman.penyaev@profitbricks.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Thu, Jun 01, 2017 at 06:08:47PM +0200, Roman Pen wrote: > Submission of requests on linux aio is a bit tricky and can lead to > requests completions on submission path: > > 44713c9e8547 ("linux-aio: Handle io_submit() failure gracefully") > 0ed93d84edab ("linux-aio: process completions from ioq_submit()") > > That means that any coroutine which has been yielded in order to wait > for completion can be resumed from submission path and be eventually > terminated (freed). > > The following use-after-free crash was observed when IO throttling > was enabled: > > Program received signal SIGSEGV, Segmentation fault. > [Switching to Thread 0x7f5813dff700 (LWP 56417)] > virtqueue_unmap_sg (elem=0x7f5804009a30, len=1, vq=<optimized out>) at virtio.c:252 > (gdb) bt > #0 virtqueue_unmap_sg (elem=0x7f5804009a30, len=1, vq=<optimized out>) at virtio.c:252 > ^^^^^^^^^^^^^^ > remember the address > > #1 virtqueue_fill (vq=0x5598b20d21b0, elem=0x7f5804009a30, len=1, idx=0) at virtio.c:282 > #2 virtqueue_push (vq=0x5598b20d21b0, elem=elem@entry=0x7f5804009a30, len=<optimized out>) at virtio.c:308 > #3 virtio_blk_req_complete (req=req@entry=0x7f5804009a30, status=status@entry=0 '\000') at virtio-blk.c:61 > #4 virtio_blk_rw_complete (opaque=<optimized out>, ret=0) at virtio-blk.c:126 > #5 blk_aio_complete (acb=0x7f58040068d0) at block-backend.c:923 > #6 coroutine_trampoline (i0=<optimized out>, i1=<optimized out>) at coroutine-ucontext.c:78 > > (gdb) p * elem > $8 = {index = 77, out_num = 2, in_num = 1, > in_addr = 0x7f5804009ad8, out_addr = 0x7f5804009ae0, > in_sg = 0x0, out_sg = 0x7f5804009a50} > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ > 'in_sg' and 'out_sg' are invalid. > e.g. it is impossible that 'in_sg' is zero, > instead its value must be equal to: > > (gdb) p/x 0x7f5804009ad8 + sizeof(elem->in_addr[0]) + 2 * sizeof(elem->out_addr[0]) > $26 = 0x7f5804009af0 > > Seems 'elem' was corrupted. Meanwhile another thread raised an abort: > > Thread 12 (Thread 0x7f57f2ffd700 (LWP 56426)): > #0 raise () from /lib/x86_64-linux-gnu/libc.so.6 > #1 abort () from /lib/x86_64-linux-gnu/libc.so.6 > #2 qemu_coroutine_enter (co=0x7f5804009af0) at qemu-coroutine.c:113 > #3 qemu_co_queue_run_restart (co=0x7f5804009a30) at qemu-coroutine-lock.c:60 > #4 qemu_coroutine_enter (co=0x7f5804009a30) at qemu-coroutine.c:119 > ^^^^^^^^^^^^^^^^^^ > WTF?? this is equal to elem from crashed thread > > #5 qemu_co_queue_run_restart (co=0x7f57e7f16ae0) at qemu-coroutine-lock.c:60 > #6 qemu_coroutine_enter (co=0x7f57e7f16ae0) at qemu-coroutine.c:119 > #7 qemu_co_queue_run_restart (co=0x7f5807e112a0) at qemu-coroutine-lock.c:60 > #8 qemu_coroutine_enter (co=0x7f5807e112a0) at qemu-coroutine.c:119 > #9 qemu_co_queue_run_restart (co=0x7f5807f17820) at qemu-coroutine-lock.c:60 > #10 qemu_coroutine_enter (co=0x7f5807f17820) at qemu-coroutine.c:119 > #11 qemu_co_queue_run_restart (co=0x7f57e7f18e10) at qemu-coroutine-lock.c:60 > #12 qemu_coroutine_enter (co=0x7f57e7f18e10) at qemu-coroutine.c:119 > #13 qemu_co_enter_next (queue=queue@entry=0x5598b1e742d0) at qemu-coroutine-lock.c:106 > #14 timer_cb (blk=0x5598b1e74280, is_write=<optimized out>) at throttle-groups.c:419 > > Crash can be explained by access of 'co' object from the loop inside > qemu_co_queue_run_restart(): > > while ((next = QSIMPLEQ_FIRST(&co->co_queue_wakeup))) { > QSIMPLEQ_REMOVE_HEAD(&co->co_queue_wakeup, co_queue_next); > ^^^^^^^^^^^^^^^^^^^^ > on each iteration 'co' is accessed, > but 'co' can be already freed > > qemu_coroutine_enter(next); > } > > When 'next' coroutine is resumed (entered) it can in its turn resume > 'co', and eventually free it. That's why we see 'co' (which was freed) > has the same address as 'elem' from the first backtrace. > > The fix is obvious: use temporary queue and do not touch coroutine after > first qemu_coroutine_enter() is invoked. > > The issue is quite rare and happens every ~12 hours on very high IO > and CPU load (building linux kernel with -j512 inside guest) when IO > throttling is enabled. With the fix applied guest is running ~35 hours > and is still alive so far. > > Signed-off-by: Roman Pen <roman.penyaev@profitbricks.com> > Cc: Paolo Bonzini <pbonzini@redhat.com> > Cc: Fam Zheng <famz@redhat.com> > Cc: Stefan Hajnoczi <stefanha@redhat.com> > Cc: Kevin Wolf <kwolf@redhat.com> > Cc: qemu-devel@nongnu.org > --- > v3: > Comments tweaks suggested by Stefan. > v2: > Comments tweaks suggested by Paolo. > > util/qemu-coroutine-lock.c | 19 +++++++++++++++++-- > util/qemu-coroutine.c | 5 +++++ > 2 files changed, 22 insertions(+), 2 deletions(-) Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
On Thu, Jun 01, 2017 at 06:08:47PM +0200, Roman Pen wrote: > Submission of requests on linux aio is a bit tricky and can lead to > requests completions on submission path: > > 44713c9e8547 ("linux-aio: Handle io_submit() failure gracefully") > 0ed93d84edab ("linux-aio: process completions from ioq_submit()") > > That means that any coroutine which has been yielded in order to wait > for completion can be resumed from submission path and be eventually > terminated (freed). > > The following use-after-free crash was observed when IO throttling > was enabled: > > Program received signal SIGSEGV, Segmentation fault. > [Switching to Thread 0x7f5813dff700 (LWP 56417)] > virtqueue_unmap_sg (elem=0x7f5804009a30, len=1, vq=<optimized out>) at virtio.c:252 > (gdb) bt > #0 virtqueue_unmap_sg (elem=0x7f5804009a30, len=1, vq=<optimized out>) at virtio.c:252 > ^^^^^^^^^^^^^^ > remember the address > > #1 virtqueue_fill (vq=0x5598b20d21b0, elem=0x7f5804009a30, len=1, idx=0) at virtio.c:282 > #2 virtqueue_push (vq=0x5598b20d21b0, elem=elem@entry=0x7f5804009a30, len=<optimized out>) at virtio.c:308 > #3 virtio_blk_req_complete (req=req@entry=0x7f5804009a30, status=status@entry=0 '\000') at virtio-blk.c:61 > #4 virtio_blk_rw_complete (opaque=<optimized out>, ret=0) at virtio-blk.c:126 > #5 blk_aio_complete (acb=0x7f58040068d0) at block-backend.c:923 > #6 coroutine_trampoline (i0=<optimized out>, i1=<optimized out>) at coroutine-ucontext.c:78 > > (gdb) p * elem > $8 = {index = 77, out_num = 2, in_num = 1, > in_addr = 0x7f5804009ad8, out_addr = 0x7f5804009ae0, > in_sg = 0x0, out_sg = 0x7f5804009a50} > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ > 'in_sg' and 'out_sg' are invalid. > e.g. it is impossible that 'in_sg' is zero, > instead its value must be equal to: > > (gdb) p/x 0x7f5804009ad8 + sizeof(elem->in_addr[0]) + 2 * sizeof(elem->out_addr[0]) > $26 = 0x7f5804009af0 > > Seems 'elem' was corrupted. Meanwhile another thread raised an abort: > > Thread 12 (Thread 0x7f57f2ffd700 (LWP 56426)): > #0 raise () from /lib/x86_64-linux-gnu/libc.so.6 > #1 abort () from /lib/x86_64-linux-gnu/libc.so.6 > #2 qemu_coroutine_enter (co=0x7f5804009af0) at qemu-coroutine.c:113 > #3 qemu_co_queue_run_restart (co=0x7f5804009a30) at qemu-coroutine-lock.c:60 > #4 qemu_coroutine_enter (co=0x7f5804009a30) at qemu-coroutine.c:119 > ^^^^^^^^^^^^^^^^^^ > WTF?? this is equal to elem from crashed thread > > #5 qemu_co_queue_run_restart (co=0x7f57e7f16ae0) at qemu-coroutine-lock.c:60 > #6 qemu_coroutine_enter (co=0x7f57e7f16ae0) at qemu-coroutine.c:119 > #7 qemu_co_queue_run_restart (co=0x7f5807e112a0) at qemu-coroutine-lock.c:60 > #8 qemu_coroutine_enter (co=0x7f5807e112a0) at qemu-coroutine.c:119 > #9 qemu_co_queue_run_restart (co=0x7f5807f17820) at qemu-coroutine-lock.c:60 > #10 qemu_coroutine_enter (co=0x7f5807f17820) at qemu-coroutine.c:119 > #11 qemu_co_queue_run_restart (co=0x7f57e7f18e10) at qemu-coroutine-lock.c:60 > #12 qemu_coroutine_enter (co=0x7f57e7f18e10) at qemu-coroutine.c:119 > #13 qemu_co_enter_next (queue=queue@entry=0x5598b1e742d0) at qemu-coroutine-lock.c:106 > #14 timer_cb (blk=0x5598b1e74280, is_write=<optimized out>) at throttle-groups.c:419 > > Crash can be explained by access of 'co' object from the loop inside > qemu_co_queue_run_restart(): > > while ((next = QSIMPLEQ_FIRST(&co->co_queue_wakeup))) { > QSIMPLEQ_REMOVE_HEAD(&co->co_queue_wakeup, co_queue_next); > ^^^^^^^^^^^^^^^^^^^^ > on each iteration 'co' is accessed, > but 'co' can be already freed > > qemu_coroutine_enter(next); > } > > When 'next' coroutine is resumed (entered) it can in its turn resume > 'co', and eventually free it. That's why we see 'co' (which was freed) > has the same address as 'elem' from the first backtrace. > > The fix is obvious: use temporary queue and do not touch coroutine after > first qemu_coroutine_enter() is invoked. > > The issue is quite rare and happens every ~12 hours on very high IO > and CPU load (building linux kernel with -j512 inside guest) when IO > throttling is enabled. With the fix applied guest is running ~35 hours > and is still alive so far. > > Signed-off-by: Roman Pen <roman.penyaev@profitbricks.com> > Cc: Paolo Bonzini <pbonzini@redhat.com> > Cc: Fam Zheng <famz@redhat.com> > Cc: Stefan Hajnoczi <stefanha@redhat.com> > Cc: Kevin Wolf <kwolf@redhat.com> > Cc: qemu-devel@nongnu.org > --- > v3: > Comments tweaks suggested by Stefan. > v2: > Comments tweaks suggested by Paolo. > > util/qemu-coroutine-lock.c | 19 +++++++++++++++++-- > util/qemu-coroutine.c | 5 +++++ > 2 files changed, 22 insertions(+), 2 deletions(-) Thanks, applied to my block tree: https://github.com/stefanha/qemu/commits/block Stefan
diff --git a/util/qemu-coroutine-lock.c b/util/qemu-coroutine-lock.c index 6328eed26bc6..b44b5d55ebad 100644 --- a/util/qemu-coroutine-lock.c +++ b/util/qemu-coroutine-lock.c @@ -77,10 +77,25 @@ void coroutine_fn qemu_co_queue_wait(CoQueue *queue, CoMutex *mutex) void qemu_co_queue_run_restart(Coroutine *co) { Coroutine *next; + QSIMPLEQ_HEAD(, Coroutine) tmp_queue_wakeup = + QSIMPLEQ_HEAD_INITIALIZER(tmp_queue_wakeup); trace_qemu_co_queue_run_restart(co); - while ((next = QSIMPLEQ_FIRST(&co->co_queue_wakeup))) { - QSIMPLEQ_REMOVE_HEAD(&co->co_queue_wakeup, co_queue_next); + + /* Because "co" has yielded, any coroutine that we wakeup can resume it. + * If this happens and "co" terminates, co->co_queue_wakeup becomes + * invalid memory. Therefore, use a temporary queue and do not touch + * the "co" coroutine as soon as you enter another one. + * + * In its turn resumed "co" can pupulate "co_queue_wakeup" queue with + * new coroutines to be woken up. The caller, who has resumed "co", + * will be responsible for traversing the same queue, which may cause + * a different wakeup order but not any missing wakeups. + */ + QSIMPLEQ_CONCAT(&tmp_queue_wakeup, &co->co_queue_wakeup); + + while ((next = QSIMPLEQ_FIRST(&tmp_queue_wakeup))) { + QSIMPLEQ_REMOVE_HEAD(&tmp_queue_wakeup, co_queue_next); qemu_coroutine_enter(next); } } diff --git a/util/qemu-coroutine.c b/util/qemu-coroutine.c index 486af9a62275..d6095c1d5aa4 100644 --- a/util/qemu-coroutine.c +++ b/util/qemu-coroutine.c @@ -126,6 +126,11 @@ void qemu_aio_coroutine_enter(AioContext *ctx, Coroutine *co) qemu_co_queue_run_restart(co); + /* Beware, if ret == COROUTINE_YIELD and qemu_co_queue_run_restart() + * has started any other coroutine, "co" might have been reentered + * and even freed by now! So be careful and do not touch it. + */ + switch (ret) { case COROUTINE_YIELD: return;
Submission of requests on linux aio is a bit tricky and can lead to requests completions on submission path: 44713c9e8547 ("linux-aio: Handle io_submit() failure gracefully") 0ed93d84edab ("linux-aio: process completions from ioq_submit()") That means that any coroutine which has been yielded in order to wait for completion can be resumed from submission path and be eventually terminated (freed). The following use-after-free crash was observed when IO throttling was enabled: Program received signal SIGSEGV, Segmentation fault. [Switching to Thread 0x7f5813dff700 (LWP 56417)] virtqueue_unmap_sg (elem=0x7f5804009a30, len=1, vq=<optimized out>) at virtio.c:252 (gdb) bt #0 virtqueue_unmap_sg (elem=0x7f5804009a30, len=1, vq=<optimized out>) at virtio.c:252 ^^^^^^^^^^^^^^ remember the address #1 virtqueue_fill (vq=0x5598b20d21b0, elem=0x7f5804009a30, len=1, idx=0) at virtio.c:282 #2 virtqueue_push (vq=0x5598b20d21b0, elem=elem@entry=0x7f5804009a30, len=<optimized out>) at virtio.c:308 #3 virtio_blk_req_complete (req=req@entry=0x7f5804009a30, status=status@entry=0 '\000') at virtio-blk.c:61 #4 virtio_blk_rw_complete (opaque=<optimized out>, ret=0) at virtio-blk.c:126 #5 blk_aio_complete (acb=0x7f58040068d0) at block-backend.c:923 #6 coroutine_trampoline (i0=<optimized out>, i1=<optimized out>) at coroutine-ucontext.c:78 (gdb) p * elem $8 = {index = 77, out_num = 2, in_num = 1, in_addr = 0x7f5804009ad8, out_addr = 0x7f5804009ae0, in_sg = 0x0, out_sg = 0x7f5804009a50} ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 'in_sg' and 'out_sg' are invalid. e.g. it is impossible that 'in_sg' is zero, instead its value must be equal to: (gdb) p/x 0x7f5804009ad8 + sizeof(elem->in_addr[0]) + 2 * sizeof(elem->out_addr[0]) $26 = 0x7f5804009af0 Seems 'elem' was corrupted. Meanwhile another thread raised an abort: Thread 12 (Thread 0x7f57f2ffd700 (LWP 56426)): #0 raise () from /lib/x86_64-linux-gnu/libc.so.6 #1 abort () from /lib/x86_64-linux-gnu/libc.so.6 #2 qemu_coroutine_enter (co=0x7f5804009af0) at qemu-coroutine.c:113 #3 qemu_co_queue_run_restart (co=0x7f5804009a30) at qemu-coroutine-lock.c:60 #4 qemu_coroutine_enter (co=0x7f5804009a30) at qemu-coroutine.c:119 ^^^^^^^^^^^^^^^^^^ WTF?? this is equal to elem from crashed thread #5 qemu_co_queue_run_restart (co=0x7f57e7f16ae0) at qemu-coroutine-lock.c:60 #6 qemu_coroutine_enter (co=0x7f57e7f16ae0) at qemu-coroutine.c:119 #7 qemu_co_queue_run_restart (co=0x7f5807e112a0) at qemu-coroutine-lock.c:60 #8 qemu_coroutine_enter (co=0x7f5807e112a0) at qemu-coroutine.c:119 #9 qemu_co_queue_run_restart (co=0x7f5807f17820) at qemu-coroutine-lock.c:60 #10 qemu_coroutine_enter (co=0x7f5807f17820) at qemu-coroutine.c:119 #11 qemu_co_queue_run_restart (co=0x7f57e7f18e10) at qemu-coroutine-lock.c:60 #12 qemu_coroutine_enter (co=0x7f57e7f18e10) at qemu-coroutine.c:119 #13 qemu_co_enter_next (queue=queue@entry=0x5598b1e742d0) at qemu-coroutine-lock.c:106 #14 timer_cb (blk=0x5598b1e74280, is_write=<optimized out>) at throttle-groups.c:419 Crash can be explained by access of 'co' object from the loop inside qemu_co_queue_run_restart(): while ((next = QSIMPLEQ_FIRST(&co->co_queue_wakeup))) { QSIMPLEQ_REMOVE_HEAD(&co->co_queue_wakeup, co_queue_next); ^^^^^^^^^^^^^^^^^^^^ on each iteration 'co' is accessed, but 'co' can be already freed qemu_coroutine_enter(next); } When 'next' coroutine is resumed (entered) it can in its turn resume 'co', and eventually free it. That's why we see 'co' (which was freed) has the same address as 'elem' from the first backtrace. The fix is obvious: use temporary queue and do not touch coroutine after first qemu_coroutine_enter() is invoked. The issue is quite rare and happens every ~12 hours on very high IO and CPU load (building linux kernel with -j512 inside guest) when IO throttling is enabled. With the fix applied guest is running ~35 hours and is still alive so far. Signed-off-by: Roman Pen <roman.penyaev@profitbricks.com> Cc: Paolo Bonzini <pbonzini@redhat.com> Cc: Fam Zheng <famz@redhat.com> Cc: Stefan Hajnoczi <stefanha@redhat.com> Cc: Kevin Wolf <kwolf@redhat.com> Cc: qemu-devel@nongnu.org --- v3: Comments tweaks suggested by Stefan. v2: Comments tweaks suggested by Paolo. util/qemu-coroutine-lock.c | 19 +++++++++++++++++-- util/qemu-coroutine.c | 5 +++++ 2 files changed, 22 insertions(+), 2 deletions(-)