On Thu, 2009-10-01 at 15:59 -0400, Douglas Gilbert wrote: > iceberg wrote: > > KERNEL_VERSION: 2.6.31 > > DESCRIBE: > > Driver sg.c might sleep in atomic context, because it calls > > scsi_device_put under lock_kernel. > > > > /drivers/scsi/sg.c:306: > > static int > > sg_open(struct inode *inode, struct file *filp) > > { > > ... > > lock_kernel(); > > ... > > error_out: > > if (retval) > > scsi_device_put(sdp->device); > > ... > > > > Path to might_sleep macro from scsi_device_put: > > 1. scsi_device_put calls put_device at ./drivers/scsi/scsi.c:1111 > > 2. put_device calls kobject_put at ./drivers/base/core.c:1038 > > 3. kobject_put calls kref_put at ./lib/kobject.c > > 4. kref_put may call callback function kobject_release at ./lib/kref.c if > > refcount becomes zero, which might_sleep because it calls user event. Details: > > 5.1 kobject_cleanup calls kobject_uevent at ./lib/kobject.c:555 > > 5.2 kobject_uevent calls kobject_uevent_env at ./lib/kobject_uevent.c:282 > > 5.3 kobject_uevent_env calls call_usermodehelper_exec at > > include/linux/kmod.h:83 > > 5.4 call_usermodehelper_exec calls wait_for_completion at ./kernel/kmod.c:481 > > 5.5 wait_for_completion calls wait_for_common at ./kernel/sched.c:5710 > > 5.6 wait_for_common calls might_sleep at ./kernels/sched.c:5692 > > > > Found by: Linux Driver Verification > > This patch to sg_open() does one (and only one) unlock_kernel() > prior to scsi_device_put(). I presume sg_put_dev() may also > sleep so the unlock_kernel() is moved before it as well. > > Hopefully Tomo will comment. Really, this isn't a bug, so no fix is required. The analysis is wrong on two levels. Firstly scsi_device_put() is designed to be called from interrupt/locked context and secondly lock_kernel isn't actually a lock taking interrupt context anyway. The BLK is a strange beast; it's recursive and it's actually transparently dropped and reacquired over schedule, so you can sleep by design with the BKL held. James -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html