Commit 19f545b6 authored by Mike Galbraith's avatar Mike Galbraith Committed by Ingo Molnar
Browse files

zram: Use local lock to protect per-CPU data 



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]

Signed-off-by: default avatarMike Galbraith <umgwanakikbuti@gmail.com>
Signed-off-by: default avatarSebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Acked-by: default avatarPeter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20200527201119.1692513-8-bigeasy@linutronix.de
parent ed19f192

drivers/block/zram/zcomp.c

+5 −2
Original line number Diff line number Diff line
@@ -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");

drivers/block/zram/zcomp.h

+3 −0
Original line number Diff line number Diff line
@@ -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;