path: root/lib
diff options
authorThomas Gleixner <>2021-11-08 18:33:25 -0800
committerLinus Torvalds <>2021-11-09 10:02:50 -0800
commit723aca2085166bb7213bf6af1729ddfd94c25a3e (patch)
tree4ed63787d79c76909e646d3233a5bd259f68e795 /lib
parent839b395eb9c13ae56ea5fc3ca9802734a72293f0 (diff)
mm/scatterlist: replace the !preemptible warning in sg_miter_stop()
sg_miter_stop() checks for disabled preemption before unmapping a page via kunmap_atomic(). The kernel doc mentions under context that preemption must be disabled if SG_MITER_ATOMIC is set. There is no active requirement for the caller to have preemption disabled before invoking sg_mitter_stop(). The sg_mitter_*() implementation itself has no such requirement. In fact, preemption is disabled by kmap_atomic() as part of sg_miter_next() and remains disabled as long as there is an active SG_MITER_ATOMIC mapping. This is a consequence of kmap_atomic() and not a requirement for sg_mitter_*() itself. The user chooses SG_MITER_ATOMIC because it uses the API in a context where blocking is not possible or blocking is possible but he chooses a lower weight mapping which is not available on all CPUs and so it might need less overhead to setup at a price that now preemption will be disabled. The kmap_atomic() implementation on PREEMPT_RT does not disable preemption. It simply disables CPU migration to ensure that the task remains on the same CPU while the caller remains preemptible. This in turn triggers the warning in sg_miter_stop() because preemption is allowed. The PREEMPT_RT and !PREEMPT_RT implementation of kmap_atomic() disable pagefaults as a requirement. It is sufficient to check for this instead of disabled preemption. Check for disabled pagefault handler in the SG_MITER_ATOMIC case. Remove the "preemption disabled" part from the kernel doc as the sg_milter*() implementation does not care. [ commit description] Link: Signed-off-by: Thomas Gleixner <> Signed-off-by: Sebastian Andrzej Siewior <> Signed-off-by: Andrew Morton <> Signed-off-by: Linus Torvalds <>
Diffstat (limited to 'lib')
1 files changed, 4 insertions, 7 deletions
diff --git a/lib/scatterlist.c b/lib/scatterlist.c
index abb3432ed744..d5e82e4a57ad 100644
--- a/lib/scatterlist.c
+++ b/lib/scatterlist.c
@@ -828,8 +828,7 @@ static bool sg_miter_get_next_page(struct sg_mapping_iter *miter)
* stops @miter.
* Context:
- * Don't care if @miter is stopped, or not proceeded yet.
- * Otherwise, preemption disabled if the SG_MITER_ATOMIC is set.
+ * Don't care.
* Returns:
* true if @miter contains the valid mapping. false if end of sg
@@ -865,8 +864,7 @@ EXPORT_SYMBOL(sg_miter_skip);
* @miter->addr and @miter->length point to the current mapping.
* Context:
- * Preemption disabled if SG_MITER_ATOMIC. Preemption must stay disabled
- * till @miter is stopped. May sleep if !SG_MITER_ATOMIC.
+ * May sleep if !SG_MITER_ATOMIC.
* Returns:
* true if @miter contains the next mapping. false if end of sg
@@ -906,8 +904,7 @@ EXPORT_SYMBOL(sg_miter_next);
* need to be released during iteration.
* Context:
- * Preemption disabled if the SG_MITER_ATOMIC is set. Don't care
- * otherwise.
+ * Don't care otherwise.
void sg_miter_stop(struct sg_mapping_iter *miter)
@@ -922,7 +919,7 @@ void sg_miter_stop(struct sg_mapping_iter *miter)
if (miter->__flags & SG_MITER_ATOMIC) {
- WARN_ON_ONCE(preemptible());
+ WARN_ON_ONCE(!pagefault_disabled());
} else