Messages in this thread Patch in this message | | | From | Sebastian Andrzej Siewior <> | Subject | [PATCH v3 7/7] zram: Use local lock to protect per-CPU data | Date | Wed, 27 May 2020 22:11:19 +0200 |
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From: Mike Galbraith <umgwanakikbuti@gmail.com>
The zcomp driver uses per-CPU compression. The per-CPU data pointer is acquired with get_cpu_ptr() which implicitly disables preemption. It allocates memory inside the preempt disabled region which conflicts with the PREEMPT_RT semantics.
Replace the implicit preemption control with an explicit local lock. This allows RT kernels to substitute it with a real per CPU lock, which serializes the access but keeps the code section preemptible. On non RT kernels this maps to preempt_disable() as before, i.e. no functional change.
[bigeasy: Use local_lock(), description, drop reordering]
Cc: Minchan Kim <minchan@kernel.org> Cc: Nitin Gupta <ngupta@vflare.org> Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> Signed-off-by: Mike Galbraith <umgwanakikbuti@gmail.com> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> --- drivers/block/zram/zcomp.c | 7 +++++-- drivers/block/zram/zcomp.h | 3 +++ 2 files changed, 8 insertions(+), 2 deletions(-)
diff --git a/drivers/block/zram/zcomp.c b/drivers/block/zram/zcomp.c index 912e3e63d8a09..5ee8e3fae5516 100644 --- a/drivers/block/zram/zcomp.c +++ b/drivers/block/zram/zcomp.c @@ -110,12 +110,13 @@ ssize_t zcomp_available_show(const char *comp, char *buf) struct zcomp_strm *zcomp_stream_get(struct zcomp *comp) { - return get_cpu_ptr(comp->stream); + local_lock(&comp->stream->lock); + return this_cpu_ptr(comp->stream); } void zcomp_stream_put(struct zcomp *comp) { - put_cpu_ptr(comp->stream); + local_unlock(&comp->stream->lock); } int zcomp_compress(struct zcomp_strm *zstrm, @@ -159,6 +160,8 @@ int zcomp_cpu_up_prepare(unsigned int cpu, struct hlist_node *node) int ret; zstrm = per_cpu_ptr(comp->stream, cpu); + local_lock_init(&zstrm->lock); + ret = zcomp_strm_init(zstrm, comp); if (ret) pr_err("Can't allocate a compression stream\n"); diff --git a/drivers/block/zram/zcomp.h b/drivers/block/zram/zcomp.h index 72c2ee4d843ed..40f6420f4b2e9 100644 --- a/drivers/block/zram/zcomp.h +++ b/drivers/block/zram/zcomp.h @@ -5,8 +5,11 @@ #ifndef _ZCOMP_H_ #define _ZCOMP_H_ +#include <linux/local_lock.h> struct zcomp_strm { + /* The members ->buffer and ->tfm are protected by ->lock. */ + local_lock_t lock; /* compression/decompression buffer */ void *buffer; struct crypto_comp *tfm; -- 2.27.0.rc0
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