Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1685928

Re: [PATCH 1/2] arm64: mm: abort uaccess retries upon fatal signal

Show all headers | View raw

Hi Mark,

On 11/07/17 15:19, Mark Rutland wrote:
> When there's a fatal signal pending, arm64's do_page_fault()
> implementation returns 0. The intent is that we'll return to the
> faulting userspace instruction, delivering the signal on the way.
> 
> However, if we take a fatal signal during fixing up a uaccess, this
> results in a return to the faulting kernel instruction, which will be
> instantly retried, resulting in the same fault being taken forever. As
> the task never reaches userspace, the signal is not delivered, and the
> task is left unkillable. While the task is stuck in this state, it can
> inhibit the forward progress of the system.
> 
> To avoid this, we must ensure that when a fatal signal is pending, we
> apply any necessary fixup for a faulting kernel instruction. Thus we
> will return to an error path, and it is up to that code to make forward
> progress towards delivering the fatal signal.

VM_FAULT_RETRY's 'I released your locks' behaviour is pretty nasty, but this
looks right. FWIW:
Reviewed-by: James Morse <james.morse@arm.com>

I also gave this a spin through LTP on Juno, based on v4.12-defconfig:
Tested-by: James Morse <james.morse@arm.com>


Thanks,

James

Back to linux.kernel | Previous | Next — Previous in thread | Find similar | Unroll thread

Thread

[PATCH 0/2] Fatal signal handing within uaccess faults Mark Rutland <mark.rutland@arm.com> - 2017-07-11 16:30 +0200
  [PATCH 1/2] arm64: mm: abort uaccess retries upon fatal signal Mark Rutland <mark.rutland@arm.com> - 2017-07-11 16:30 +0200
    Re: [PATCH 1/2] arm64: mm: abort uaccess retries upon fatal signal Will Deacon <will.deacon@arm.com> - 2017-07-11 17:00 +0200
    Re: [PATCH 1/2] arm64: mm: abort uaccess retries upon fatal signal James Morse <james.morse@arm.com> - 2017-07-12 19:30 +0200

csiph-web