While testing an older driver on an -RT kernel (currently using
-V0.7.37-03), I noticed something strange.
The driver was triggering a "sleeping function called from invalid
context" BUG(). It was coming from a case where the driver was doing
a __get_free_page(GFP_ATOMIC) while interrupts were disabled (example
trace below). I know this is probably real bug and it shouldn't be
allocating memory with interrupts disabled, but shouldn't this be
possible? Isn't the role of GFP_ATOMIC to say that "this caller
cannot sleep".
To produce the following trace, I wrote a simple moudle which just has
this as its init_module routine:
local_irq_disable();
p = __get_free_page(GFP_ATOMIC);
local_irq_enable();
And here's the trace:
BUG: sleeping function called from invalid context insmod(2126) at
kernel/rt.c:1448
in_atomic():0 [00000000], irqs_disabled():1
[<c0102fa3>] dump_stack+0x23/0x30 (20)
[<c01133c5>] __might_sleep+0xe5/0x100 (36)
[<c012fbb8>] __spin_lock+0x38/0x60 (24)
[<c012fc8d>] _spin_lock_irqsave+0x1d/0x30 (16)
[<c0140e5c>] buffered_rmqueue+0x1c/0x190 (40)
[<c01413ce>] __alloc_pages+0x34e/0x390 (76)
[<c0141437>] __get_free_pages+0x27/0x50 (12)
[<c883205a>] kmod_init+0x5a/0x74 [kmod] (24)
[<c0138232>] sys_init_module+0x232/0x260 (28)
[<c010299c>] syscall_call+0x7/0xb (-8124)
---------------------------
| preempt count: 00000001 ]
| 1-level deep critical section nesting:
----------------------------------------
.. [<c0133e3d>] .... print_traces+0x1d/0x60
.....[<c0102fa3>] .. ( <= dump_stack+0x23/0x30)
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