tree 7f5349d9e8b59633b9f8a7bd9bcd45ace1d21a41
parent 0e44dc383787b472a7f13564c6bd8a44cc07d408
author Linus Torvalds <torvalds@g5.osdl.org> 1147370929 -0700
committer Linus Torvalds <torvalds@g5.osdl.org> 1147370929 -0700

ptrace_attach: fix possible deadlock schenario with irqs

Eric Biederman points out that we can't take the task_lock while holding
tasklist_lock for writing, because another CPU that holds the task lock
might take an interrupt that then tries to take tasklist_lock for writing.

Which would be a nasty deadlock, with one CPU spinning forever in an
interrupt handler (although admittedly you need to really work at
triggering it ;)

Since the ptrace_attach() code is special and very unusual, just make it
be extra careful, and use trylock+repeat to avoid the possible deadlock.

Cc: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Roland McGrath <roland@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>