From 4617721c502b2ddaa4e324e86da4997edf738fa5 Mon Sep 17 00:00:00 2001 From: Steven Rostedt Date: Wed, 2 Sep 2026 09:55:01 -0400 Subject: ftrace: Synchronize the initialization of ftrace_ops There's some internal state that ftrace_ops needs to have set, but since it can be declared outside of the ftrace.c code, it calls ftrace_ops_init() on the ops in every global function. The issue is that if two tasks call it on the same ops at the same time it is possible to have the initialization of one corrupt the initialization of the other call. Create a ops_mutex to use to synchronize every initialization of the ftrace_ops. The mutex is taken within checking the ftrace_ops flag that states it was initializied but the flag is checked again after the mutex has been taken. Checking first outside the mutex allows it to shortcut having to take the mutex. But then the check needs to be done again after the mute is taken in case of races. Cc: stable@vger.kernel.org Link: https://patch.msgid.link/20260902095501.6b59af20@gandalf.local.home Fixes: f04f24fb7e48d ("ftrace, kprobes: Fix a deadlock on ftrace_regex_lock") Reported-by: sashiko-bot@kernel.org Close: https://lore.kernel.org/all/20260829025528.49A831F000E9@smtp.kernel.org/ Signed-off-by: Steven Rostedt --- drivers/md/dm-zero.c | 81 ++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 81 insertions(+) create mode 100644 drivers/md/dm-zero.c (limited to 'drivers/md/dm-zero.c') diff --git a/drivers/md/dm-zero.c b/drivers/md/dm-zero.c new file mode 100644 index 000000000..9a0bb623e --- /dev/null +++ b/drivers/md/dm-zero.c @@ -0,0 +1,81 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Copyright (C) 2003 Jana Saout + * + * This file is released under the GPL. + */ + +#include + +#include +#include +#include + +#define DM_MSG_PREFIX "zero" + +/* + * Construct a dummy mapping that only returns zeros + */ +static int zero_ctr(struct dm_target *ti, unsigned int argc, char **argv) +{ + if (argc != 0) { + ti->error = "No arguments required"; + return -EINVAL; + } + + /* + * Silently drop discards, avoiding -EOPNOTSUPP. + */ + ti->num_discard_bios = 1; + ti->discards_supported = true; + + return 0; +} + +/* + * Return zeros only on reads + */ +static int zero_map(struct dm_target *ti, struct bio *bio) +{ + switch (bio_op(bio)) { + case REQ_OP_READ: + if (bio->bi_opf & REQ_RAHEAD) { + /* readahead of null bytes only wastes buffer cache */ + return DM_MAPIO_KILL; + } + zero_fill_bio(bio); + break; + case REQ_OP_WRITE: + case REQ_OP_DISCARD: + /* writes get silently dropped */ + break; + default: + return DM_MAPIO_KILL; + } + + bio_endio(bio); + + /* accepted bio, don't make new request */ + return DM_MAPIO_SUBMITTED; +} + +static void zero_io_hints(struct dm_target *ti, struct queue_limits *limits) +{ + limits->max_hw_discard_sectors = UINT_MAX; + limits->discard_granularity = 512; +} + +static struct target_type zero_target = { + .name = "zero", + .version = {1, 2, 0}, + .features = DM_TARGET_NOWAIT, + .module = THIS_MODULE, + .ctr = zero_ctr, + .map = zero_map, + .io_hints = zero_io_hints, +}; +module_dm(zero); + +MODULE_AUTHOR("Jana Saout "); +MODULE_DESCRIPTION(DM_NAME " dummy target returning zeros"); +MODULE_LICENSE("GPL"); -- cgit v1.3.1