From: Mikulas Patocka Date: Tue, 2 Jan 2018 19:01:34 +0000 (-0500) Subject: alpha: fix crash if pthread_create races with signal delivery X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=629bfb9f6b0d47c4ec805ec587acca059b68e924;p=pandora-kernel.git alpha: fix crash if pthread_create races with signal delivery commit 21ffceda1c8b3807615c40d440d7815e0c85d366 upstream. On alpha, a process will crash if it attempts to start a thread and a signal is delivered at the same time. The crash can be reproduced with this program: https://cygwin.com/ml/cygwin/2014-11/msg00473.html The reason for the crash is this: * we call the clone syscall * we go to the function copy_process * copy process calls copy_thread_tls, it is a wrapper around copy_thread * copy_thread sets the tls pointer: childti->pcb.unique = regs->r20 * copy_thread sets regs->r20 to zero * we go back to copy_process * copy process checks "if (signal_pending(current))" and returns -ERESTARTNOINTR * the clone syscall is restarted, but this time, regs->r20 is zero, so the new thread is created with zero tls pointer * the new thread crashes in start_thread when attempting to access tls The comment in the code says that setting the register r20 is some compatibility with OSF/1. But OSF/1 doesn't use the CLONE_SETTLS flag, so we don't have to zero r20 if CLONE_SETTLS is set. This patch fixes the bug by zeroing regs->r20 only if CLONE_SETTLS is not set. Signed-off-by: Mikulas Patocka Signed-off-by: Matt Turner [bwh: Backported to 3.2: - Remove the settls variable, which was done upstream in commit 25906730ec01 "alpha: reorganize copy_process(), prepare to saner fork_idle()"] - Adjust context] Signed-off-by: Ben Hutchings --- Reading git-diff-tree failed