Messages in this thread | | | From | Guenter Roeck <> | Subject | Re: [PATCH] iov_iter: separate direction from flavour | Date | Sun, 4 Jul 2021 13:28:44 -0700 |
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On 7/4/21 12:04 PM, Linus Torvalds wrote: > On Sun, Jul 4, 2021 at 11:54 AM Guenter Roeck <linux@roeck-us.net> wrote: >> >> No, I still see the same warning, with the same traceback. I did make sure >> that the code is executed by adding a printk in front of it. > > And that printk() hits before the WARN_ON_ONCE() hits? >
Yes:
[ 8.604785] Run /init as init process [ 8.604933] ##################### calling force_uaccess_begin() [ 8.609691] ------------[ cut here ]------------ [ 8.609795] WARNING: CPU: 0 PID: 1 at lib/iov_iter.c:468 iov_iter_init+0x35/0x58 [ 8.609979] CPU: 0 PID: 1 Comm: init Not tainted 5.13.0-09608-g678b12cd4025-dirty #1
Either case, the code doesn't do anything, because force_uaccess_begin() is already called. With more added debugging:
##################### calling force_uaccess_begin() ############## force_uaccess_begin(), called from run_init_process+0x80/0x8c ############## force_uaccess_begin(), called from load_flat_binary+0x10e/0x92a
> Funky. That sounds to me like something is then doing > set_fs(KERNEL_DS) again later, but it's also possible that I've been > dropped on my head a few too many times as a young child, and am > missing something completely obvious. > > Can somebody put me out of my misery and say "Oh, Linus, please take > your meds - you're missing xyz..." >
Turns out that, at least on m68k/nommu, USER_DS and KERNEL_DS are the same.
#define USER_DS MAKE_MM_SEG(TASK_SIZE) #define KERNEL_DS MAKE_MM_SEG(0xFFFFFFFF)
and:
#define TASK_SIZE (0xFFFFFFFFUL)
I didn't check mps2, but I strongly suspect the same is true there.
Guenter
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