Hello,
On 20.09.22 11:42, Vlastimil Babka wrote:
On 9/20/22 10:20, Alexander Atanasov wrote:
In (060807f841ac mm, slub: make remaining slub_debug related attributes
read-only failslab) it was made RO.
"read-only) failslab was made RO" ?
Yep.
I think it became a collateral victim to the other two options
(sanity_checks and trace) for which the reasons are perfectly valid.
The commit also mentioned that modifying the flags is not protected in any
way, see below.
Yes, indeed.
+static ssize_t failslab_store(struct kmem_cache *s, const char *buf,
+ size_t length)
+{
+ if (s->refcount > 1)
+ return -EINVAL;
+
+ s->flags &= ~SLAB_FAILSLAB;
+ if (buf[0] == '1')
+ s->flags |= SLAB_FAILSLAB;
Could we at least use a temporary variable to set up the final value and
then do a WRITE_ONCE() to s->flags, so the compiler is not allowed to do
some funky stuff? Assuming this is really the only place where we modify
s->flags during runtime, so we can't miss other updates due to RMW.
Since it is set or clear - instead of temporary variable and potentially
two writes and RMW issues i would suggest this:
+ if (buf[0] == '1')
+ s->flags |= SLAB_FAILSLAB;
+ else
+ s->flags &= ~SLAB_FAILSLAB;
If at some point more places need to modify the flags at runtime they
can switch to atomic bit ops.
--
Regards,
Alexander Atanasov
