Re: [Qemu-devel] [PATCH] ide: fix double free

[Paolo Bonzini <pbonzini@redhat.com>]

Il 03/07/2014 04:23, ChenLiang ha scritto:
> Program received signal SIGABRT, Aborted.
> 0x00007fd548355b55 in raise () from /lib64/libc.so.6
> (gdb) bt
> #0  0x00007fd548355b55 in raise () from /lib64/libc.so.6
> #1  0x00007fd548357131 in abort () from /lib64/libc.so.6
> #2  0x00007fd548393e0f in __libc_message () from /lib64/libc.so.6
> #3  0x00007fd548399618 in malloc_printerr () from /lib64/libc.so.6
> #4  0x00007fd54b15e80e in free_and_trace (mem=0x7fd54beb2230) at vl.c:2815
> #5  0x00007fd54b3453cd in qemu_aio_release (p=0x7fd54beb2230) at block.c:4813
> #6  0x00007fd54b15717d in dma_complete (dbs=0x7fd54beb2230, ret=0) at dma-helpers.c:132
> #7  0x00007fd54b157253 in dma_bdrv_cb (opaque=0x7fd54beb2230, ret=0) at dma-helpers.c:148
> #8  0x00007fd54b344db8 in bdrv_co_em_bh (opaque=0x7fd54bea4b30) at block.c:4676
> #9  0x00007fd54b335a72 in aio_bh_poll (ctx=0x7fd54bcec990) at async.c:81
> #10 0x00007fd54b34b1b4 in aio_poll (ctx=0x7fd54bcec990, blocking=false) at aio-posix.c:188
> #11 0x00007fd54b335ee0 in aio_ctx_dispatch (source=0x7fd54bcec990, callback=0x0, user_data=0x0) at async.c:211
> #12 0x00007fd549e3669a in g_main_context_dispatch () from /usr/lib64/libglib-2.0.so.0
> #13 0x00007fd54b348c45 in glib_pollfds_poll () at main-loop.c:190
> #14 0x00007fd54b348d3d in os_host_main_loop_wait (timeout=0) at main-loop.c:235
> #15 0x00007fd54b348e2f in main_loop_wait (nonblocking=0) at main-loop.c:484
> #16 0x00007fd54b15b0f8 in main_loop () at vl.c:2007
> #17 0x00007fd54b162a35 in main (argc=57, argv=0x7fff152720a8, envp=0x7fff15272278) at vl.c:4526
>
> (gdb) bt
> #0  qemu_aio_release (p=0x7f86420ebec0) at block.c:4811
> #1  0x00007f86412b617d in dma_complete (dbs=0x7f86420ebec0, ret=0) at dma-helpers.c:132
> #2  0x00007f86412b65ab in dma_aio_cancel (acb=0x7f86420ebec0) at dma-helpers.c:192
> #3  0x00007f86414a3996 in bdrv_aio_cancel (acb=0x7f86420ebec0) at block.c:4559
> #4  0x00007f86413906af in ide_bus_reset (bus=0x7f8641fe3a20) at hw/ide/core.c:2056
> #5  0x00007f86413967d6 in piix3_reset (opaque=0x7f8641fe32a0) at hw/ide/piix.c:114
> #6  0x00007f86412b9a37 in qemu_devices_reset () at vl.c:1829
> #7  0x00007f86412b9aef in qemu_system_reset (report=true) at vl.c:1842
> #8  0x00007f86412b9fe2 in main_loop_should_exit () at vl.c:1971
> #9  0x00007f86412ba100 in main_loop () at vl.c:2011
> #10 0x00007f86412c1a35 in main (argc=57, argv=0x7fff2e827d38, envp=0x7fff2e827f08) at vl.c:4526

Ok, this is the same as your previous backtrace.  The bug is still the 
same: dma_bdrv_cb must not be called dma_aio_cancel has finished the 
recursive call to bdrv_aio_cancel.

> BTW, is it better to rename dbs->in_cancel to dbs->canceled ?

If we were to apply my patch, yes.  But with the current logic 
"in_cancel" says "are we inside the recursive call to bdrv_aio_cancel" 
so I think the answer is no.  My patch is just a band-aid, I don't think 
it should be applied.

Paolo