Messages in this thread | | | From | Sergey Senozhatsky <> | Subject | [PATCHv2 0/4] Access console drivers list under console_sem | Date | Fri, 26 Apr 2019 14:32:58 +0900 |
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Hello,
Normally, we grab console_sem lock before we iterate consoles list, which is necessary if we want to be race free. The only exception to this rule is console_flush_on_panic(). However, it seems that we are not fully race free - register_console() iterates console drivers list in unsafe manner in several places. E.g. the following scenarion:
CPU0 CPU1 register_console() unregister_console() console_lock() for_each_console() // modify console_drivers con->foo kfree(con)
I factored out register_console() and unregister_console() and now the bulk of the work is done under console_sem. Both in register and unregister paths we now have that oddly looking thing
pr_info("console enabled/disabled"); console_unlock(); console_lock();
Which is not really odd, in fact. This is to make sure that we always print messages on all the consoles.
v2: - removed outdated comment (Petr) - factor out register_console() and always run it under console_sem (Petr) - added a patch which enusures that we always print "console disabled' on every console, before we unregister one of them
Sergey Senozhatsky (4): printk: factor out __unregister_console() code printk: remove invalid register_console() comment printk: factor out register_console() code printk: make sure we always print console disabled message
kernel/printk/printk.c | 125 +++++++++++++++++++++++++---------------- 1 file changed, 76 insertions(+), 49 deletions(-)
-- 2.21.0
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