Commit 7cbce1ea authored by Sergey Senozhatsky's avatar Sergey Senozhatsky Committed by Andrew Morton
Browse files

zram: protect recomp_algorithm_show() with ->init_lock 

sysfs handlers should be called under ->init_lock and are not supposed to
unlock it until return, otherwise e.g.  a concurrent reset() can occur. 
There is one handler that breaks that rule: recomp_algorithm_show().

Move ->init_lock handling outside of __comp_algorithm_show() (also drop it
and call zcomp_available_show() directly) so that the entire
recomp_algorithm_show() loop is protected by the lock, as opposed to
protecting individual iterations.

The patch does not need to go to -stable, as it does not fix any
runtime errors (at least I can't think of any).  It makes
recomp_algorithm_show() "atomic" w.r.t.  zram reset() (just like the
rest of zram sysfs show() handlers), that's a pretty minor change.

Link: https://lkml.kernel.org/r/20250805101946.1774112-1-senozhatsky@chromium.org


Signed-off-by: default avatarSergey Senozhatsky <senozhatsky@chromium.org>
Reported-by: default avatarSeyediman Seyedarab <imandevel@gmail.com>
Suggested-by: default avatarSeyediman Seyedarab <imandevel@gmail.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Minchan Kim <minchan@kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 79e1c242

drivers/block/zram/zram_drv.c

+8 −15
Original line number Diff line number Diff line
@@ -1225,18 +1225,6 @@ static void comp_algorithm_set(struct zram *zram, u32 prio, const char *alg) 
	zram->comp_algs[prio] = alg;

}



static ssize_t __comp_algorithm_show(struct zram *zram, u32 prio,

				     char *buf, ssize_t at)

{

	ssize_t sz;



	down_read(&zram->init_lock);

	sz = zcomp_available_show(zram->comp_algs[prio], buf, at);

	up_read(&zram->init_lock);



	return sz;

}



static int __comp_algorithm_store(struct zram *zram, u32 prio, const char *buf)

{

	char *compressor;
@@ -1387,8 +1375,12 @@ static ssize_t comp_algorithm_show(struct device *dev, 
				   char *buf)

{

	struct zram *zram = dev_to_zram(dev);

	ssize_t sz;



	return __comp_algorithm_show(zram, ZRAM_PRIMARY_COMP, buf, 0);

	down_read(&zram->init_lock);

	sz = zcomp_available_show(zram->comp_algs[ZRAM_PRIMARY_COMP], buf, 0);

	up_read(&zram->init_lock);

	return sz;

}



static ssize_t comp_algorithm_store(struct device *dev,
@@ -1412,14 +1404,15 @@ static ssize_t recomp_algorithm_show(struct device *dev, 
	ssize_t sz = 0;

	u32 prio;



	down_read(&zram->init_lock);

	for (prio = ZRAM_SECONDARY_COMP; prio < ZRAM_MAX_COMPS; prio++) {

		if (!zram->comp_algs[prio])

			continue;



		sz += sysfs_emit_at(buf, sz, "#%d: ", prio);

		sz += __comp_algorithm_show(zram, prio, buf, sz);

		sz += zcomp_available_show(zram->comp_algs[prio], buf, sz);

	}



	up_read(&zram->init_lock);

	return sz;

}