The patch titled memory ordering in __kfifo primitives has been added to the -mm tree. Its filename is memory-ordering-in-__kfifo-primitives.patch See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find out what to do about this ------------------------------------------------------ Subject: memory ordering in __kfifo primitives From: "Paul E. McKenney" <paulmck@xxxxxxxxxx> Both __kfifo_put() and __kfifo_get() have header comments stating that if there is but one concurrent reader and one concurrent writer, locking is not necessary. This is almost the case, but a couple of memory barriers are needed. Another option would be to change the header comments to remove the bit about locking not being needed, and to change the those callers who currently don't use locking to add the required locking. The attachment analyzes this approach, but the patch below seems simpler. Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx> Cc: Stelian Pop <stelian@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxx> --- kernel/kfifo.c | 28 ++++++++++++++++++++++++++++ 1 files changed, 28 insertions(+) diff -puN kernel/kfifo.c~memory-ordering-in-__kfifo-primitives kernel/kfifo.c --- a/kernel/kfifo.c~memory-ordering-in-__kfifo-primitives +++ a/kernel/kfifo.c @@ -122,6 +122,13 @@ unsigned int __kfifo_put(struct kfifo *f len = min(len, fifo->size - fifo->in + fifo->out); + /* + * Ensure that we sample the fifo->out index -before- we + * start putting bytes into the kfifo. + */ + + smp_mb(); + /* first put the data starting from fifo->in to buffer end */ l = min(len, fifo->size - (fifo->in & (fifo->size - 1))); memcpy(fifo->buffer + (fifo->in & (fifo->size - 1)), buffer, l); @@ -129,6 +136,13 @@ unsigned int __kfifo_put(struct kfifo *f /* then put the rest (if any) at the beginning of the buffer */ memcpy(fifo->buffer, buffer + l, len - l); + /* + * Ensure that we add the bytes to the kfifo -before- + * we update the fifo->in index. + */ + + smp_wmb(); + fifo->in += len; return len; @@ -154,6 +168,13 @@ unsigned int __kfifo_get(struct kfifo *f len = min(len, fifo->in - fifo->out); + /* + * Ensure that we sample the fifo->in index -before- we + * start removing bytes from the kfifo. + */ + + smp_rmb(); + /* first get the data from fifo->out until the end of the buffer */ l = min(len, fifo->size - (fifo->out & (fifo->size - 1))); memcpy(buffer, fifo->buffer + (fifo->out & (fifo->size - 1)), l); @@ -161,6 +182,13 @@ unsigned int __kfifo_get(struct kfifo *f /* then get the rest (if any) from the beginning of the buffer */ memcpy(buffer + l, fifo->buffer, len - l); + /* + * Ensure that we remove the bytes from the kfifo -before- + * we update the fifo->out index. + */ + + smp_mb(); + fifo->out += len; return len; _ Patches currently in -mm which might be from paulmck@xxxxxxxxxx are radix-tree-rcu-lockless-readside.patch adix-tree-rcu-lockless-readside-update.patch rcu-add-lock-annotations-to-rcu_bh_torture_read_lockunlock.patch memory-ordering-in-__kfifo-primitives.patch srcu-3-rcu-variant-permitting-read-side-blocking.patch srcu-3-rcu-variant-permitting-read-side-blocking-fix.patch srcu-3-add-srcu-operations-to-rcutorture.patch srcu-3-add-srcu-operations-to-rcutorture-fix.patch add-srcu-based-notifier-chains.patch add-srcu-based-notifier-chains-cleanup.patch srcu-report-out-of-memory-errors.patch srcu-report-out-of-memory-errors-fixlet.patch cpufreq-make-the-transition_notifier-chain-use-srcu.patch - To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html