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2007-07-21x86_64: mcelog tolerant level cleanupTim Hockin
Background: The MCE handler has several paths that it can take, depending on various conditions of the MCE status and the value of the 'tolerant' knob. The exact semantics are not well defined and the code is a bit twisty. Description: This patch makes the MCE handler's behavior more clear by documenting the behavior for various 'tolerant' levels. It also fixes or enhances several small things in the handler. Specifically: * If RIPV is set it is not safe to restart, so set the 'no way out' flag rather than the 'kill it' flag. * Don't panic() on correctable MCEs. * If the _OVER bit is set *and* the _UC bit is set (meaning possibly dropped uncorrected errors), set the 'no way out' flag. * Use EIPV for testing whether an app can be killed (SIGBUS) rather than RIPV. According to docs, EIPV indicates that the error is related to the IP, while RIPV simply means the IP is valid to restart from. * Don't clear the MCi_STATUS registers until after the panic() path. This leaves the status bits set after the panic() so clever BIOSes can find them (and dumb BIOSes can do nothing). This patch also calls nonseekable_open() in mce_open (as suggested by akpm). Result: Tolerant levels behave almost identically to how they always have, but not it's well defined. There's a slightly higher chance of panic()ing when multiple errors happen (a good thing, IMHO). If you take an MBE and panic(), the error status bits are not cleared. Alternatives: None. Testing: I used software to inject correctable and uncorrectable errors. With tolerant = 3, the system usually survives. With tolerant = 2, the system usually panic()s (PCC) but not always. With tolerant = 1, the system always panic()s. When the system panic()s, the BIOS is able to detect that the cause of death was an MC4. I was not able to reproduce the case of a non-PCC error in userspace, with EIPV, with (tolerant < 3). That will be rare at best. Signed-off-by: Tim Hockin <thockin@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Andi Kleen <ak@suse.de> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-02[PATCH] x86-64: Dynamically adjust machine check intervalTim Hockin
Background: We've found that MCEs (specifically DRAM SBEs) tend to come in bunches, especially when we are trying really hard to stress the system out. The current MCE poller uses a static interval which does not care whether it has or has not found MCEs recently. Description: This patch makes the MCE poller adjust the polling interval dynamically. If we find an MCE, poll 2x faster (down to 10 ms). When we stop finding MCEs, poll 2x slower (up to check_interval seconds). The check_interval tunable becomes the max polling interval. The "Machine check events logged" printk() is rate limited to the check_interval, which should be identical behavior to the old functionality. Result: If you start to take a lot of correctable errors (not exceptions), you log them faster and more accurately (less chance of overflowing the MCA registers). If you don't take a lot of errors, you will see no change. Alternatives: I considered simply reducing the polling interval to 10 ms immediately and keeping it there as long as we continue to find errors. This felt a bit heavy handed, but does perform significantly better for the default check_interval of 5 minutes (we're using a few seconds when testing for DRAM errors). I could be convinced to go with this, if anyone felt it was not too aggressive. Testing: I used an error-injecting DIMM to create lots of correctable DRAM errors and verified that the polling interval accelerates. The printk() only happens once per check_interval seconds. Patch: This patch is against 2.6.21-rc7. Signed-Off-By: Tim Hockin <thockin@google.com> Signed-off-by: Andi Kleen <ak@suse.de>
2007-02-13[PATCH] x86-64: Allow to run a program when a machine check event is detectedAndi Kleen
When a machine check event is detected (including a AMD RevF threshold overflow event) allow to run a "trigger" program. This allows user space to react to such events sooner. The trigger is configured using a new trigger entry in the machinecheck sysfs interface. It is currently shared between all CPUs. I also fixed the AMD threshold handler to run the machine check polling code immediately to actually log any events that might have caused the threshold interrupt. Also added some documentation for the mce sysfs interface. Signed-off-by: Andi Kleen <ak@suse.de>