vasily postnicov <[email protected]> added the comment:
Some code from usb_mem.c:
/*
* Do not free the memory unconditionally since we might be called
* from an interrupt context and that is BAD.
* XXX when should we really free?
*/
static void
usb_block_freemem(usb_dma_block_t *p)
{
DPRINTFN(6, ("usb_block_freemem: size=%lu\n", (u_long)p->size));
logmemory(blkfree, p, NULL, p->size, p->align);
crit_enter();
LIST_INSERT_HEAD(&usb_blk_freelist, p, next);
usb_blk_nfree++;
crit_exit();
}
So it, actually, does not free memory, does it?
Here is some code from NetBSD I found:
http://fxr.watson.org/fxr/source/dev/usb/usb_mem.c?v=NETBSD;im=10
As you can see, there is some function called usb_block_real_freemem, but (as I
understand) it is never compiled (it is between #if 0/#endif).
What is "interrupt context" and why it is so dangerous?
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