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| author | Mathieu Desnoyers <mathieu.desnoyers@efficios.com> | 2022-06-22 15:46:16 -0400 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2022-08-01 15:21:29 +0200 |
| commit | 0190e4198e47fe99d002d72588f34fd62c9ab570 (patch) | |
| tree | 025ffe0425ab8aa28c0ded5bc3ca61a79019f605 /kernel | |
| parent | 91caa5ae242465c3ab9fd473e50170faa7e944f4 (diff) | |
| download | lwn-0190e4198e47fe99d002d72588f34fd62c9ab570.tar.gz lwn-0190e4198e47fe99d002d72588f34fd62c9ab570.zip | |
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@gmail.com/ [1]
Link: https://lore.kernel.org/lkml/258546133.12151.1655739550814.JavaMail.zimbra@efficios.com/ [2]
Link: https://lore.kernel.org/lkml/87pmj1enjh.fsf@email.froward.int.ebiederm.org/ [3]
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/lkml/20220622194617.1155957-1-mathieu.desnoyers@efficios.com
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/rseq.c | 23 |
1 files changed, 8 insertions, 15 deletions
diff --git a/kernel/rseq.c b/kernel/rseq.c index 97ac20b4f738..81d7dc80787b 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) |