diff mbox series

random: clarify PRNG MT safety guarantees

Message ID 20231004105449.367667-1-mattias.ronnblom@ericsson.com (mailing list archive)
State Accepted, archived
Delegated to: David Marchand
Headers
Series random: clarify PRNG MT safety guarantees |

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Commit Message

Mattias Rönnblom Oct. 4, 2023, 10:54 a.m. UTC 
  Clarify MT safety guarantees for unregistered non-EAL threads calling
PRNG functions in rte_random.h.

Clarify that rte_srand() is not MT safe in regards to calls to
rte_rand_max() and rte_drand().

Signed-off-by: Mattias Rönnblom <mattias.ronnblom@ericsson.com>
Suggested-by: Stephen Hemminger <stephen@networkplumber.org>
---
 lib/eal/include/rte_random.h | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

Comments

Morten Brørup Oct. 4, 2023, 12:05 p.m. UTC | #1 
> From: Mattias Rönnblom [mailto:mattias.ronnblom@ericsson.com]
> Sent: Wednesday, 4 October 2023 12.55
random: clarify PRNG MT safety guarantees
> 
> Clarify MT safety guarantees for unregistered non-EAL threads calling
> PRNG functions in rte_random.h.
> 
> Clarify that rte_srand() is not MT safe in regards to calls to
> rte_rand_max() and rte_drand().
> 
> Signed-off-by: Mattias Rönnblom <mattias.ronnblom@ericsson.com>
> Suggested-by: Stephen Hemminger <stephen@networkplumber.org>
> ---

Acked-by: Morten Brørup <mb@smartsharesystems.com>
David Marchand Oct. 6, 2023, 9:13 a.m. UTC | #2 
On Wed, Oct 4, 2023 at 1:00 PM Mattias Rönnblom
<mattias.ronnblom@ericsson.com> wrote:
>
> Clarify MT safety guarantees for unregistered non-EAL threads calling
> PRNG functions in rte_random.h.
>
> Clarify that rte_srand() is not MT safe in regards to calls to
> rte_rand_max() and rte_drand().
>
> Suggested-by: Stephen Hemminger <stephen@networkplumber.org>
> Signed-off-by: Mattias Rönnblom <mattias.ronnblom@ericsson.com>

Should it be backported along 3a4e21301c7a ("random: initialize state
for unregistered non-EAL threads") ?
Mattias Rönnblom Oct. 6, 2023, 12:18 p.m. UTC | #3 
On 2023-10-06 11:13, David Marchand wrote:
> On Wed, Oct 4, 2023 at 1:00 PM Mattias Rönnblom
> <mattias.ronnblom@ericsson.com> wrote:
>>
>> Clarify MT safety guarantees for unregistered non-EAL threads calling
>> PRNG functions in rte_random.h.
>>
>> Clarify that rte_srand() is not MT safe in regards to calls to
>> rte_rand_max() and rte_drand().
>>
>> Suggested-by: Stephen Hemminger <stephen@networkplumber.org>
>> Signed-off-by: Mattias Rönnblom <mattias.ronnblom@ericsson.com>
> 
> Should it be backported along 3a4e21301c7a ("random: initialize state
> for unregistered non-EAL threads") ?
> 
> 

I don't think that's worth the trouble, but if someone has a different 
opinion, I also don't mind if it is.
Stephen Hemminger Oct. 6, 2023, 3:58 p.m. UTC | #4 
On Fri, 6 Oct 2023 14:18:25 +0200
Mattias Rönnblom <hofors@lysator.liu.se> wrote:

> On 2023-10-06 11:13, David Marchand wrote:
> > On Wed, Oct 4, 2023 at 1:00 PM Mattias Rönnblom
> > <mattias.ronnblom@ericsson.com> wrote:  
> >>
> >> Clarify MT safety guarantees for unregistered non-EAL threads calling
> >> PRNG functions in rte_random.h.
> >>
> >> Clarify that rte_srand() is not MT safe in regards to calls to
> >> rte_rand_max() and rte_drand().
> >>
> >> Suggested-by: Stephen Hemminger <stephen@networkplumber.org>
> >> Signed-off-by: Mattias Rönnblom <mattias.ronnblom@ericsson.com>  
> > 
> > Should it be backported along 3a4e21301c7a ("random: initialize state
> > for unregistered non-EAL threads") ?
> > 
> >   
> 
> I don't think that's worth the trouble, but if someone has a different 
> opinion, I also don't mind if it is.

Agree. The initialization patch should be backported, but not this one.
David Marchand Oct. 10, 2023, 9:40 a.m. UTC | #5 
On Wed, Oct 4, 2023 at 2:06 PM Morten Brørup <mb@smartsharesystems.com> wrote:
>
> > From: Mattias Rönnblom [mailto:mattias.ronnblom@ericsson.com]
> > Sent: Wednesday, 4 October 2023 12.55
> random: clarify PRNG MT safety guarantees
> >
> > Clarify MT safety guarantees for unregistered non-EAL threads calling
> > PRNG functions in rte_random.h.
> >
> > Clarify that rte_srand() is not MT safe in regards to calls to
> > rte_rand_max() and rte_drand().
> >
> > Suggested-by: Stephen Hemminger <stephen@networkplumber.org>
> > Signed-off-by: Mattias Rönnblom <mattias.ronnblom@ericsson.com>
> Acked-by: Morten Brørup <mb@smartsharesystems.com>

Applied, thanks Mattias.
diff mbox series

Patch

diff --git a/lib/eal/include/rte_random.h b/lib/eal/include/rte_random.h
index 2edf5d210b..c12eb07ea8 100644
--- a/lib/eal/include/rte_random.h
+++ b/lib/eal/include/rte_random.h
@@ -27,8 +27,8 @@  extern "C" {
  * value.
  *
  * This function is not multi-thread safe in regards to other
- * rte_srand() calls, nor is it in relation to concurrent rte_rand()
- * calls.
+ * rte_srand() calls, nor is it in relation to concurrent rte_rand(),
+ * rte_rand_max() or rte_drand() calls.
  *
  * @param seedval
  *   The value of the seed.
@@ -41,8 +41,9 @@  rte_srand(uint64_t seedval);
  *
  * The generator is not cryptographically secure.
  *
- * If called from EAL threads or registered non-EAL threads, this function
- * is thread-safe.
+ * rte_rand(), rte_rand_max() and rte_drand() are multi-thread safe,
+ * with the exception that they may not be called by multiple
+ * _unregistered_ non-EAL threads in parallel.
  *
  * @return
  *   A pseudo-random value between 0 and (1<<64)-1.
@@ -56,8 +57,9 @@  rte_rand(void);
  * This function returns an uniformly distributed (unbiased) random
  * number less than a user-specified maximum value.
  *
- * If called from EAL threads or registered non-EAL threads, this function
- * is thread-safe.
+ * rte_rand(), rte_rand_max() and rte_drand() are multi-thread safe,
+ * with the exception that they may not be called by multiple
+ * _unregistered_ non-EAL threads in parallel.
  *
  * @param upper_bound
  *   The upper bound of the generated number.
@@ -78,8 +80,9 @@  rte_rand_max(uint64_t upper_bound);
  *
  * The generator is not cryptographically secure.
  *
- * If called from EAL threads or registered non-EAL threads, this function
- * is thread-safe.
+ * rte_rand(), rte_rand_max() and rte_drand() are multi-thread safe,
+ * with the exception that they may not be called by multiple
+ * _unregistered_ non-EAL threads in parallel.
  *
  * @return
  *   A pseudo-random value between 0 and 1.0.