What's the meaning of CONFIG_BROKEN_ON_SMP?
Hi,
I compiled a driver, ang get the following message:
CONFIG_BROKEN_ON_SMP: should be set in the kernel configuration, but isn't.
Somebody suggested to disable the kernel's SMP feature. I did, and the problem got solved.
Then, I googled the meaning of CONFIG_BROKEN_ON_SMP, but did not get definitive explanation, such as
http://cateee.net/lkddb/web-lkddb/BROKEN_ON_SMP.html
I wonder what the meaning of the configuration is. How does it work? Thx!
Quoted 3 lines · parmenides
CONFIG_BROKEN_ON_SMP: should be set in the kernel configuration, but isn't.I wonder what the meaning of the configuration is. How does it work? Thx!
Drivers (and all other kernel-mode code, actually) need to do proper locking, so that if there's a race between code running on 2 different CPUs at the same time, they don't stomp all over each other (consider the case of one CPU trying to walk a linked list at the same time that another CPU is deleting an entry from the list - this can leave the first CPU walking down a now corrupted list following now-stale pointers).
There are a lot of old buggy drivers that don't do proper locking. In a few cases, the drivers are *technically* buggy, but the bugs just happen to be in code that will manage to work anyhow *if there is only one CPU* (for instance, wrapped in a IRQ-disabled section). These drivers get BROKEN_ON_SMP attached, because they can still potentially be useful for people compiling on architectures that only support 1 processor core, or *need* the driver and don't care if they only use 1 core of the 4 they have.
The proper fix is, of course, to put proper locking in the driver - but most BROKEN_ON_SMP drivers are creeping horrorshows straight out of HP Lovecraft,
and nobody wants to invest the resources needed to fix the abandonware driver. -------------- next part --------------
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? 2014/1/25 1:27, Valdis.Kletnieks at vt.edu wote:
Quoted 21 lines · parmenides
Quoted 4 lines
CONFIG_BROKEN_ON_SMP: should be set in the kernel configuration, but isn't.I wonder what the meaning of the configuration is. How does it work? Thx!
Drivers (and all other kernel-mode code, actually) need to do proper locking, so that if there's a race between code running on 2 different CPUs at the same time, they don't stomp all over each other (consider the case of one CPU trying to walk a linked list at the same time that another CPU is deleting an entry from the list - this can leave the first CPU walking down a now corrupted list following now-stale pointers).
There are a lot of old buggy drivers that don't do proper locking. In a few cases, the drivers are *technically* buggy, but the bugs just happen to be in code that will manage to work anyhow *if there is only one CPU* (for instance, wrapped in a IRQ-disabled section). These drivers get
BROKEN_ON_SMPattached, because they can still potentially be useful for people compiling on architectures that only support 1 processor core, or *need* the driver and don't care if they only use 1 core of the 4 they have.
Quoted 4 lines
The proper fix is, of course, to put proper locking in the driver - but most
BROKEN_ON_SMPdrivers are creeping horrorshows straight out of HP Lovecraft, and nobody wants to invest the resources needed to fix the abandonware driver.
Does that mean BROKEN_ON_SMP drivers are all tagged, and they are not seen when I 'make menuconfig', if CONFIG_BROKEN_ON_SMP not be set? If so, how these drivers are tagged?