Commit f0fa7463 authored by Oliver Neukum's avatar Oliver Neukum Committed by Greg Kroah-Hartman

USB: update to Documentation

this mentions a new deadlock due to advanced power management.
Signed-off-by: default avatarOliver Neukum <oneukum@suse.de>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@suse.de>
parent 230ffc75
......@@ -436,7 +436,12 @@ post_reset; the USB core guarantees that this is true of internal
suspend/resume events as well.
If a driver wants to block all suspend/resume calls during some
critical section, it can simply acquire udev->pm_mutex.
critical section, it can simply acquire udev->pm_mutex. Note that
calls to resume may be triggered indirectly. Block IO due to memory
allocations can make the vm subsystem resume a device. Thus while
holding this lock you must not allocate memory with GFP_KERNEL or
GFP_NOFS.
Alternatively, if the critical section might call some of the
usb_autopm_* routines, the driver can avoid deadlock by doing:
......
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