On Sat, 30 Dec 2023 11:00:47 +0000 <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > The patch below does not apply to the 6.1-stable tree. > If someone wants it applied there, or to any other stable or longterm > tree, then please email the backport, including the original git commit > id to <stable@xxxxxxxxxxxxxxx>. > > To reproduce the conflict and resubmit, you may use the following commands: > > git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.1.y > git checkout FETCH_HEAD > git cherry-pick -x b803d7c664d55705831729d2f2e29c874bcd62ea > # <resolve conflicts, build, test, etc.> > git commit -s > git send-email --to '<stable@xxxxxxxxxxxxxxx>' --in-reply-to '2023123047-tuesday-whooping-6ae3@gregkh' --subject-prefix 'PATCH 6.1.y' HEAD^.. > > Possible dependencies: > > b803d7c664d5 ("ring-buffer: Fix slowpath of interrupted event") > 0aa0e5289cfe ("ring-buffer: Have rb_time_cmpxchg() set the msb counter too") > fff88fa0fbc7 ("ring-buffer: Fix a race in rb_time_cmpxchg() for 32 bit archs") > 00a8478f8f5c ("ring_buffer: Use try_cmpxchg instead of cmpxchg") > bc92b9562abc ("ring_buffer: Change some static functions to bool") > 88ca6a71dcab ("ring-buffer: Handle resize in early boot up") > > thanks, Below is the patch for 6.1 of this change, and it depends on: 20231230164736.3b8c86c4@xxxxxxxxxxxxxxxxxx -- Steve --- kernel/trace/ring_buffer.c | 81 +++++++++++++-------------------------------- 1 file changed, 24 insertions(+), 57 deletions(-) Index: test-linux.git/kernel/trace/ring_buffer.c =================================================================== --- test-linux.git.orig/kernel/trace/ring_buffer.c 2023-12-30 16:10:20.179497134 -0500 +++ test-linux.git/kernel/trace/ring_buffer.c 2023-12-30 16:10:20.175497066 -0500 @@ -705,48 +705,6 @@ rb_time_read_cmpxchg(local_t *l, unsigne return ret == expect; } -static int rb_time_cmpxchg(rb_time_t *t, u64 expect, u64 set) -{ - unsigned long cnt, top, bottom, msb; - unsigned long cnt2, top2, bottom2, msb2; - u64 val; - - /* Any interruptions in this function should cause a failure */ - cnt = local_read(&t->cnt); - - /* The cmpxchg always fails if it interrupted an update */ - if (!__rb_time_read(t, &val, &cnt2)) - return false; - - if (val != expect) - return false; - - if ((cnt & 3) != cnt2) - return false; - - cnt2 = cnt + 1; - - rb_time_split(val, &top, &bottom, &msb); - msb = rb_time_val_cnt(msb, cnt); - top = rb_time_val_cnt(top, cnt); - bottom = rb_time_val_cnt(bottom, cnt); - - rb_time_split(set, &top2, &bottom2, &msb2); - msb2 = rb_time_val_cnt(msb2, cnt); - top2 = rb_time_val_cnt(top2, cnt2); - bottom2 = rb_time_val_cnt(bottom2, cnt2); - - if (!rb_time_read_cmpxchg(&t->cnt, cnt, cnt2)) - return false; - if (!rb_time_read_cmpxchg(&t->msb, msb, msb2)) - return false; - if (!rb_time_read_cmpxchg(&t->top, top, top2)) - return false; - if (!rb_time_read_cmpxchg(&t->bottom, bottom, bottom2)) - return false; - return true; -} - #else /* 64 bits */ /* local64_t always succeeds */ @@ -760,13 +718,6 @@ static void rb_time_set(rb_time_t *t, u6 { local64_set(&t->time, val); } - -static bool rb_time_cmpxchg(rb_time_t *t, u64 expect, u64 set) -{ - u64 val; - val = local64_cmpxchg(&t->time, expect, set); - return val == expect; -} #endif /* @@ -3607,20 +3558,36 @@ __rb_reserve_next(struct ring_buffer_per } else { u64 ts; /* SLOW PATH - Interrupted between A and C */ - a_ok = rb_time_read(&cpu_buffer->write_stamp, &info->after); - /* Was interrupted before here, write_stamp must be valid */ + + /* Save the old before_stamp */ + a_ok = rb_time_read(&cpu_buffer->before_stamp, &info->before); RB_WARN_ON(cpu_buffer, !a_ok); + + /* + * Read a new timestamp and update the before_stamp to make + * the next event after this one force using an absolute + * timestamp. This is in case an interrupt were to come in + * between E and F. + */ ts = rb_time_stamp(cpu_buffer->buffer); + rb_time_set(&cpu_buffer->before_stamp, ts); + barrier(); - /*E*/ if (write == (local_read(&tail_page->write) & RB_WRITE_MASK) && - info->after < ts && - rb_time_cmpxchg(&cpu_buffer->write_stamp, - info->after, ts)) { - /* Nothing came after this event between C and E */ + /*E*/ a_ok = rb_time_read(&cpu_buffer->write_stamp, &info->after); + /* Was interrupted before here, write_stamp must be valid */ + RB_WARN_ON(cpu_buffer, !a_ok); + barrier(); + /*F*/ if (write == (local_read(&tail_page->write) & RB_WRITE_MASK) && + info->after == info->before && info->after < ts) { + /* + * Nothing came after this event between C and F, it is + * safe to use info->after for the delta as it + * matched info->before and is still valid. + */ info->delta = ts - info->after; } else { /* - * Interrupted between C and E: + * Interrupted between C and F: * Lost the previous events time stamp. Just set the * delta to zero, and this will be the same time as * the event this event interrupted. And the events that
