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Re: [PATCH v8 2/8] xen: mapcache: Unmap first entries in buckets
On Mon, Jul 1, 2024 at 6:21 PM Anthony PERARD <anthony.perard@xxxxxxxxxx> wrote:
On Mon, Jul 01, 2024 at 04:34:53PM +0200, Edgar E. Iglesias wrote:
> On Mon, Jul 1, 2024 at 4:30 PM Edgar E. Iglesias <edgar.iglesias@xxxxxxxxx>
> wrote:
> > On Mon, Jul 1, 2024 at 3:58 PM Edgar E. Iglesias <edgar.iglesias@xxxxxxxxx>
> > wrote:
> >> Any chance you could try to get a backtrace from QEMU when it failed?
Here it is:
#3 0x00007fa8762f4472 in __GI_abort () at ./stdlib/abort.c:79
save_stage = 1
act = {__sigaction_handler = {sa_handler = 0x20, sa_sigaction = 0x20}, sa_mask = {__val = {94603440166168, 18446744073709551615, 94603406369640, 0, 0, 94603406346720, 94603440166168, 140361486774256, 0, 140361486773376, 94603401285536, 140361496232688, 94603440166096, 140361486773456, 94603401289576, 140360849280256}}, sa_flags = -1804462896, sa_restorer = 0x748f2d40}
#4 0x0000560a92230f0d in qemu_get_ram_block (addr=18446744073709551615) at ../system/physmem.c:801
block = 0x0
#5 0x0000560a922350ab in qemu_ram_block_from_host (ptr=0x7fa84e8fcd00, round_offset=false, offset=0x7fa8748f2de8) at ../system/physmem.c:2280
ram_addr = 18446744073709551615
_rcu_read_auto = 0x1
block = 0x0
host = 0x7fa84e8fcd00 ""
_rcu_read_auto = 0x7fa8751f8288
#6 0x0000560a92229669 in memory_region_from_host (ptr=0x7fa84e8fcd00, offset=0x7fa8748f2de8) at ../system/memory.c:2440
block = 0x0
#7 0x0000560a92237418 in address_space_unmap (as=0x560a94b05a20, buffer=0x7fa84e8fcd00, len=32768, is_write=true, access_len=32768) at ../system/physmem.c:3246
mr = 0x0
addr1 = 0
__PRETTY_FUNCTION__ = "address_space_unmap"
#8 0x0000560a91fd6cd3 in dma_memory_unmap (as=0x560a94b05a20, buffer=0x7fa84e8fcd00, len=32768, dir=DMA_DIRECTION_FROM_DEVICE, access_len=32768) at /root/build/qemu/include/sysemu/dma.h:236
#9 0x0000560a91fd763d in dma_blk_unmap (dbs=0x560a94d87400) at ../system/dma-helpers.c:93
i = 1
#10 0x0000560a91fd76e6 in dma_complete (dbs=0x560a94d87400, ret=0) at ../system/dma-helpers.c:105
__PRETTY_FUNCTION__ = "dma_complete"
#11 0x0000560a91fd781c in dma_blk_cb (opaque=0x560a94d87400, ret=0) at ../system/dma-helpers.c:129
dbs = 0x560a94d87400
ctx = 0x560a9448da90
cur_addr = 0
cur_len = 0
mem = 0x0
__PRETTY_FUNCTION__ = "dma_blk_cb"
#12 0x0000560a9232e974 in blk_aio_complete (acb=0x560a9448d5f0) at ../block/block-backend.c:1555
#13 0x0000560a9232ebd1 in blk_aio_read_entry (opaque=0x560a9448d5f0) at ../block/block-backend.c:1610
acb = 0x560a9448d5f0
rwco = 0x560a9448d618
qiov = 0x560a94d87460
__PRETTY_FUNCTION__ = "blk_aio_read_entry"
> > One more thing, regarding this specific patch. I don't think we should
> > clear the
> > entire entry, the next field should be kept, otherwise we'll disconnect
> > following
> > mappings that will never be found again. IIUC, this could very well be
> > causing the problem you see.
> >
> > Does the following make sense?
> >
> And here without double-freeing entry->valid_mapping:
>
> diff --git a/hw/xen/xen-mapcache.c b/hw/xen/xen-mapcache.c
> index 5f23b0adbe..667807b3b6 100644
> --- a/hw/xen/xen-mapcache.c
> +++ b/hw/xen/xen-mapcache.c
> @@ -597,7 +597,13 @@ static void
> xen_invalidate_map_cache_entry_unlocked(MapCache *mc,
> pentry->next = entry->next;
> g_free(entry);
> } else {
> - memset(entry, 0, sizeof *entry);
> + /* Invalidate mapping. */
> + entry->paddr_index = 0;
> + entry->vaddr_base = NULL;
> + entry->size = 0;
> + entry->valid_mapping = NULL;
> + entry->flags = 0;
> + /* Keep entry->next pointing to the rest of the list. */
> }
> }
I've tried this patch, and that fix the issue I've seen. I'll run more
tests on it, just in case, but there's no reason that would break
something else.
Cheers,
Thanks Anthony, I'll send out a proper patch tomorrow.
Cheers, Edgar
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