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zram: Use local lock to protect per-CPU data

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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: Mike Galbraith <umgwanakikbuti@gmail.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20200527201119.1692513-8-bigeasy@linutronix.de
This commit is contained in:
Mike Galbraith 2020-05-27 22:11:19 +02:00 committed by Ingo Molnar
parent ed19f19256
commit 19f545b6e0
2 changed files with 8 additions and 2 deletions
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7
drivers/block/zram/zcomp.c
View file

@ -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");

3
drivers/block/zram/zcomp.h
View file

@ -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;