path: root/Documentation
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authorRik van Riel <riel@redhat.com>2014-06-06 14:38:13 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2014-06-06 16:08:17 -0700
commit984d74a72076a12b400339973e8c98fd2fcd90e5 (patch)
treed36c81545c10dbfa1513b8392aa10478eac7d13e /Documentation
parent310bf8f74927d0b945cd3e11dc5cef961ec04fd1 (diff)
sysrq: rcu-ify __handle_sysrq
Echoing values into /proc/sysrq-trigger seems to be a popular way to get information out of the kernel. However, dumping information about thousands of processes, or hundreds of CPUs to serial console can result in IRQs being blocked for minutes, resulting in various kinds of cascade failures. The most common failure is due to interrupts being blocked for a very long time. This can lead to things like failed IO requests, and other things the system cannot easily recover from. This problem is easily fixable by making __handle_sysrq use RCU instead of spin_lock_irqsave. This leaves the warning that RCU grace periods have not elapsed for a long time, but the system will come back from that automatically. It also leaves sysrq-from-irq-context when the sysrq keys are pressed, but that is probably desired since people want that to work in situations where the system is already hosed. The callers of register_sysrq_key and unregister_sysrq_key appear to be capable of sleeping. Signed-off-by: Rik van Riel <riel@redhat.com> Reported-by: Madper Xie <cxie@redhat.com> Cc: Randy Dunlap <rdunlap@infradead.org> Cc: Richard Weinberger <richard@nod.at> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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