linux-kernel - [PATCH] zram: do not lookup algorithm in backends table

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Date:   Wed, 22 Jun 2022 11:35:01 +0900
From:   Sergey Senozhatsky <senozhatsky@...omium.org>
To:     Minchan Kim <minchan@...nel.org>, Nitin Gupta <ngupta@...are.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
        Sergey Senozhatsky <senozhatsky@...omium.org>
Subject: [PATCH] zram: do not lookup algorithm in backends table

Always use crypto_has_comp() so that crypto can lookup module,
call usermodhelper to load the modules, wait for usermodhelper
to finish and so on. Otherwise crypto will do all of these steps
under CPU hot-plug lock and this looks like too much stuff to
handle under the CPU hot-plug lock. Besides this can end up in
a deadlock when usermodhelper triggers a code path that attempts
to lock the CPU hot-plug lock, that zram already holds.

Signed-off-by: Sergey Senozhatsky <senozhatsky@...omium.org>
---
 drivers/block/zram/zcomp.c | 6 ------
 1 file changed, 6 deletions(-)

diff --git a/drivers/block/zram/zcomp.c b/drivers/block/zram/zcomp.c
index 052aa3f65514..398eb9e24eff 100644
--- a/drivers/block/zram/zcomp.c
+++ b/drivers/block/zram/zcomp.c
@@ -63,12 +63,6 @@ static int zcomp_strm_init(struct zcomp_strm *zstrm, struct zcomp *comp)
 
 bool zcomp_available_algorithm(const char *comp)
 {
-	int i;
-
-	i = sysfs_match_string(backends, comp);
-	if (i >= 0)
-		return true;
-
 	/*
 	 * Crypto does not ignore a trailing new line symbol,
 	 * so make sure you don't supply a string containing
-- 
2.37.0.rc0.104.g0611611a94-goog