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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] xc_gntshr_unmap problems (BUG(s) in xen-gntalloc?)
Hi,
On 28 Aug 2014, at 14:50, David Vrabel <david.vrabel@xxxxxxxxxx> wrote:
> On 27/08/14 22:33, Dave Scott wrote:
>> I notice xc_gntshr_munmap for Linux simply calls 'munmap'
>>
>> static int linux_gntshr_munmap(xc_gntshr *xcg, xc_osdep_handle h,
>> void *start_address, uint32_t count)
>> {
>> return munmap(start_address, count);
>> }
>
> munmap() needs a byte length, not a page count.
>
> When using xc_gntshr_munmap() with multiple pages this results in none
> of the grefs being deleted (unshared and freed) since a mapping to some
> of the grefs in the set remain.
Aha, good spot. I worked around this in my test program by calling
xc_gntshr_munmap with (count * 4096) and it’s no longer leaking.
> This doesn't appear to explain why they're not deleted by the device is
> closed.
After rebuilding xen-gntalloc with your change I couldn’t reproduce this. I
tried all combinations of
* map 1 or 2 pages
* unmap 0, 1 or 2 pages
and, although some of the iterations did run out of grant references (as
expected), nothing seemed to be leaked over a close.
>
>> -- so I guess the problem is with the xen-gntalloc driver?
>>
>> If I share single pages at a time then it triggers a BUG:
>> $ sudo ./test-gnt 1
>> [ 148.564281] BUG: unable to handle kernel paging request at
>> ffffc908001bff20
>> [ 148.564299] IP: [<ffffffff813acf93>] gnttab_query_foreign_access+0x13/0x20
>> [ 148.564312] PGD 3d520067 PUD 0
>> [ 148.564317] Oops: 0000 [#1] SMP
>> [ 148.564322] CPU 0
>> [ 148.564325] Modules linked in: xenfs xen_evtchn xen_gntalloc xen_gntdev
>> lp parport
>> [ 148.564337]
>> [ 148.564340] Pid: 897, comm: test-gnt Not tainted 3.2.0-67-generic
>> #101-Ubuntu
>> [ 148.564348] RIP: e030:[<ffffffff813acf93>] [<ffffffff813acf93>]
>> gnttab_query_foreign_access+0x13/0x20
>> [ 148.564356] RSP: e02b:ffff88003c655da0 EFLAGS: 00010286
>> [ 148.564360] RAX: ffffc900001c0000 RBX: ffff88003cdb9e40 RCX:
>> 0000000000000000
>> [ 148.564365] RDX: 0000000000000000 RSI: 000000000007026e RDI:
>> 00000000ffffffe4
>> [ 148.564371] RBP: ffff88003c655dd8 R08: 0000000000000000 R09:
>> 000000000003725f
>> [ 148.564376] R10: ffffea0000ef3680 R11: 0000000000000000 R12:
>> ffff88003cdb9e40
>> [ 148.564381] R13: 0000000000000000 R14: ffff88003c655e80 R15:
>> 0000000000000000
>> [ 148.564389] FS: 00007ffe79406740(0000) GS:ffff88003fc00000(0000)
>> knlGS:0000000000000000
>> [ 148.564394] CS: e033 DS: 0000 ES: 0000 CR0: 000000008005003b
>> [ 148.564400] CR2: ffffc908001bff20 CR3: 000000003cdc6000 CR4:
>> 0000000000000660
>> [ 148.564406] DR0: 0000000000000000 DR1: 0000000000000000 DR2:
>> 0000000000000000
>> [ 148.564412] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7:
>> 0000000000000400
>> [ 148.564418] Process test-gnt (pid: 897, threadinfo ffff88003c654000, task
>> ffff88003cdd4500)
>> [ 148.564423] Stack:
>> [ 148.564426] ffffffffa000d1a5 ffff88003c655dd8 ffffffff813adbdb
>> 00000000ffffffe4
>> [ 148.564435] 0000000000000000 00000000ffffffe4 ffff88003cdb9e40
>> ffff88003c655e68
>> [ 148.564443] ffffffffa000d848 ffff88003cc47790 ffff88003c5a8dc0
>> ffff8800041aeba8
>> [ 148.564452] Call Trace:
>> [ 148.564459] [<ffffffffa000d1a5>] ? __del_gref+0x105/0x150 [xen_gntalloc]
>> [ 148.564465] [<ffffffff813adbdb>] ? gnttab_grant_foreign_access+0x2b/0x80
>> [ 148.564471] [<ffffffffa000d848>] add_grefs+0x1c8/0x2b0 [xen_gntalloc]
>> [ 148.564478] [<ffffffffa000da28>] gntalloc_ioctl_alloc+0xf8/0x160
>> [xen_gntalloc]
>> [ 148.564485] [<ffffffffa000dae0>] gntalloc_ioctl+0x50/0x64 [xen_gntalloc]
>> [ 148.564492] [<ffffffff8118d45a>] do_vfs_ioctl+0x8a/0x340
>> [ 148.564498] [<ffffffff811456b3>] ? do_munmap+0x1f3/0x2f0
>> [ 148.564504] [<ffffffff8118d7a1>] sys_ioctl+0x91/0xa0
>> [ 148.564510] [<ffffffff8166bd42>] system_call_fastpath+0x16/0x1b
>> [ 148.564515] Code: f8 48 8b 15 98 89 b6 00 66 89 04 fa 5d c3 66 2e 0f 1f
>> 84 00 00 00 00 00 55 48 89 e5 66 66 66 66 90 48 8b 05 78 89 b6 00 89 ff 5d
>> <0f> b7 04 f8 83 e0 18 c3 0f 1f 44 00 00 55 48 89 e5 66 66 66 66
>> [ 148.564577] RIP [<ffffffff813acf93>]
>> gnttab_query_foreign_access+0x13/0x20
>> [ 148.564583] RSP <ffff88003c655da0>
>> [ 148.564586] CR2: ffffc908001bff20
>> [ 148.564591] ---[ end trace 57b3a513f0d79bd6 ]---
>
> Does this patch fix the oops?
Yes, I’ve left my test case running for several hours with no sign of trouble.
Thanks!
Dave
>
> 8<-------------------------------------
> xen/gntalloc: safely delete grefs in add_grefs() undo path
>
> If a gref could not be added (perhaps because the limit has been
> reached or there are no more grant references available). The undo
> path may crash because __del_gref() frees the gref while it is being
> used for a list iteration.
>
> A comment suggests that using list_for_each_entry() is safe since the
> gref isn't removed from the list being iterated over, but it is freed
> and thus list_for_each_entry_safe() must be used.
>
> Also, explicitly delete the gref from the per-file list, even though
> this is not strictly necessary.
>
> Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>
> ---
> drivers/xen/gntalloc.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/xen/gntalloc.c b/drivers/xen/gntalloc.c
> index 787d179..b8af1ba 100644
> --- a/drivers/xen/gntalloc.c
> +++ b/drivers/xen/gntalloc.c
> @@ -124,7 +124,7 @@ static int add_grefs(struct
> ioctl_gntalloc_alloc_gref *op,
> int i, rc, readonly;
> LIST_HEAD(queue_gref);
> LIST_HEAD(queue_file);
> - struct gntalloc_gref *gref;
> + struct gntalloc_gref *gref, *next;
>
> readonly = !(op->flags & GNTALLOC_FLAG_WRITABLE);
> rc = -ENOMEM;
> @@ -162,9 +162,9 @@ undo:
> mutex_lock(&gref_mutex);
> gref_size -= (op->count - i);
>
> - list_for_each_entry(gref, &queue_file, next_file) {
> - /* __del_gref does not remove from queue_file */
> + list_for_each_entry_safe(gref, next, &queue_file, next_file) {
> __del_gref(gref);
> + list_del(&gref->next_file);
> }
>
> /* It's possible for the target domain to map the just-allocated grant
> --
> 1.7.10.4
>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@xxxxxxxxxxxxx
> http://lists.xen.org/xen-devel
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