The following commit has been merged into the sched/core branch of tip: Commit-ID: c040fc3cb4ce18e1be54df6294f6a4004d2664ec Gitweb: https://git.kernel.org/tip/c040fc3cb4ce18e1be54df6294f6a4004d2664ec Author: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx> AuthorDate: Wed, 22 Jun 2022 15:46:16 -04:00 Committer: Peter Zijlstra <peterz@xxxxxxxxxxxxx> CommitterDate: Sat, 30 Jul 2022 10:14:18 +02:00 rseq: Deprecate RSEQ_CS_FLAG_NO_RESTART_ON_* flags The pretty much unused RSEQ_CS_FLAG_NO_RESTART_ON_* flags introduce complexity in rseq, and are subtly buggy [1]. Solving those issues requires introducing additional complexity in the rseq implementation for each supported architecture. Considering that it complexifies the rseq ABI, I am proposing that we deprecate those flags. [2] So far there appears to be consensus from maintainers of user-space projects impacted by this feature that its removal would be a welcome simplification. [3] The deprecation approach proposed here is to issue WARN_ON_ONCE() when encountering those flags and kill the offending process with sigsegv. This should allow us to quickly identify whether anyone yells at us for removing this. Link: https://lore.kernel.org/lkml/20220618182515.95831-1-minhquangbui99@xxxxxxxxx/ [1] Link: https://lore.kernel.org/lkml/258546133.12151.1655739550814.JavaMail.zimbra@xxxxxxxxxxxx/ [2] Link: https://lore.kernel.org/lkml/87pmj1enjh.fsf@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/ [3] Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> Link: https://lore.kernel.org/lkml/20220622194617.1155957-1-mathieu.desnoyers@xxxxxxxxxxxx --- kernel/rseq.c | 23 ++++++++--------------- 1 file changed, 8 insertions(+), 15 deletions(-) diff --git a/kernel/rseq.c b/kernel/rseq.c index 97ac20b..81d7dc8 100644 --- a/kernel/rseq.c +++ b/kernel/rseq.c @@ -18,8 +18,9 @@ #define CREATE_TRACE_POINTS #include <trace/events/rseq.h> -#define RSEQ_CS_PREEMPT_MIGRATE_FLAGS (RSEQ_CS_FLAG_NO_RESTART_ON_MIGRATE | \ - RSEQ_CS_FLAG_NO_RESTART_ON_PREEMPT) +#define RSEQ_CS_NO_RESTART_FLAGS (RSEQ_CS_FLAG_NO_RESTART_ON_PREEMPT | \ + RSEQ_CS_FLAG_NO_RESTART_ON_SIGNAL | \ + RSEQ_CS_FLAG_NO_RESTART_ON_MIGRATE) /* * @@ -175,23 +176,15 @@ static int rseq_need_restart(struct task_struct *t, u32 cs_flags) u32 flags, event_mask; int ret; + if (WARN_ON_ONCE(cs_flags & RSEQ_CS_NO_RESTART_FLAGS)) + return -EINVAL; + /* Get thread flags. */ ret = get_user(flags, &t->rseq->flags); if (ret) return ret; - /* Take critical section flags into account. */ - flags |= cs_flags; - - /* - * Restart on signal can only be inhibited when restart on - * preempt and restart on migrate are inhibited too. Otherwise, - * a preempted signal handler could fail to restart the prior - * execution context on sigreturn. - */ - if (unlikely((flags & RSEQ_CS_FLAG_NO_RESTART_ON_SIGNAL) && - (flags & RSEQ_CS_PREEMPT_MIGRATE_FLAGS) != - RSEQ_CS_PREEMPT_MIGRATE_FLAGS)) + if (WARN_ON_ONCE(flags & RSEQ_CS_NO_RESTART_FLAGS)) return -EINVAL; /* @@ -203,7 +196,7 @@ static int rseq_need_restart(struct task_struct *t, u32 cs_flags) t->rseq_event_mask = 0; preempt_enable(); - return !!(event_mask & ~flags); + return !!event_mask; } static int clear_rseq_cs(struct task_struct *t)
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