commit 44234adcdce38f83c56e05f808ce656175b4beeb
author Frederic Weisbecker <fweisbec@gmail.com> Wed Dec 09 09:25:48 2009 +0100
committer Ingo Molnar <mingo@elte.hu> Wed Dec 09 09:48:20 2009 +0100
tree caff2ca7bbf4bf7c0b12652caf739bcc6db5f4d3
parent c937fe20cb6d9e24c6ad5f9f0c64d64c78411057

hw-breakpoints: Modify breakpoints without unregistering them

Currently, when ptrace needs to modify a breakpoint, like disabling
it, changing its address, type or len, it calls
modify_user_hw_breakpoint(). This latter will perform the heavy and
racy task of unregistering the old breakpoint and registering a new
one.

This is racy as someone else might steal the reserved breakpoint
slot under us, which is undesired as the breakpoint is only
supposed to be modified, sometimes in the middle of a debugging
workflow. We don't want our slot to be stolen in the middle.

So instead of unregistering/registering the breakpoint, just
disable it while we modify its breakpoint fields and re-enable it
after if necessary.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Prasad <prasad@linux.vnet.ibm.com>
LKML-Reference: <1260347148-5519-1-git-send-regression-fweisbec@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>