[Xen-devel] Xen scheduling bug?

["Stephen C. Tweedie" <sct@xxxxxxxxxx>]

Hi all,

The arch/x86_64/kernel/entry-xen.S linux-2.6-xen.hg contains:

sysret_careful:
        CFI_RESTORE_STATE
        bt $TIF_NEED_RESCHED,%edx
        jnc sysret_signal
        XEN_BLOCK_EVENTS(%rsi)          <<<<<<<<<<<<<<
        pushq %rdi
        CFI_ADJUST_CFA_OFFSET 8
        call schedule
        popq  %rdi
        CFI_ADJUST_CFA_OFFSET -8
        jmp sysret_check
sret_careful:
The equivalent non-Xen chunk is:

sysret_careful:
        CFI_RESTORE_STATE
        bt $TIF_NEED_RESCHED,%edx
        jnc sysret_signal
        TRACE_IRQS_ON
        sti                             <<<<<<<<<<<<<<
        pushq %rdi
        CFI_ADJUST_CFA_OFFSET 8
        call schedule
        popq  %rdi
        CFI_ADJUST_CFA_OFFSET -8
        jmp sysret_check

Note the marked lines --- Xen is turning irqs _off_ at this point, when
non-Xen is turning them on.  I just noticed it when merging the
irqtracing code.

Bug?

--Stephen



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