Messages in this thread Patch in this message | | | From | John Ogness <> | Subject | [PATCH printk v2 4/8] printk: nbcon: Add buffer management | Date | Fri, 28 Jul 2023 02:08:29 +0206 |
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From: Thomas Gleixner <tglx@linutronix.de>
In case of hostile takeovers it must be ensured that the previous owner cannot scribble over the output buffer of the emergency/panic context. This is achieved by:
- Adding a global output buffer instance for the panic context. This is the only situation where hostile takeovers can occur and there is always at most 1 panic context.
- Allocating an output buffer per console upon console registration. This buffer is used by the console owner when not in panic context.
- Choosing the appropriate buffer is handled in the acquire/release functions.
Co-developed-by: John Ogness <john.ogness@linutronix.de> Signed-off-by: John Ogness <john.ogness@linutronix.de> Signed-off-by: Thomas Gleixner (Intel) <tglx@linutronix.de> --- include/linux/console.h | 7 +++++++ kernel/printk/internal.h | 6 ++++++ kernel/printk/printk.c | 6 ------ kernel/printk/printk_nbcon.c | 26 ++++++++++++++++++++++++-- 4 files changed, 37 insertions(+), 8 deletions(-)
diff --git a/include/linux/console.h b/include/linux/console.h index e06cd1ce3e82..d2bcd2c190a7 100644 --- a/include/linux/console.h +++ b/include/linux/console.h @@ -233,6 +233,7 @@ enum nbcon_prio { }; struct console; +struct printk_buffers; /** * struct nbcon_context - Context for console acquire/release @@ -242,6 +243,7 @@ struct console; * @unsafe: This context is in an unsafe section * @hostile: Acquire console by hostile takeover * @takeover_unsafe: Acquire console by hostile takeover even if unsafe + * @pbufs: Pointer to the text buffer for this context */ struct nbcon_context { /* members set by caller */ @@ -251,6 +253,9 @@ struct nbcon_context { unsigned int unsafe : 1; unsigned int hostile : 1; unsigned int takeover_unsafe : 1; + + /* members set by acquire */ + struct printk_buffers *pbufs; }; /** @@ -274,6 +279,7 @@ struct nbcon_context { * @node: hlist node for the console list * * @nbcon_state: State for nbcon consoles + * @pbufs: Pointer to nbcon private buffer */ struct console { char name[16]; @@ -296,6 +302,7 @@ struct console { /* nbcon console specific members */ atomic_t __private nbcon_state; + struct printk_buffers *pbufs; }; #ifdef CONFIG_LOCKDEP diff --git a/kernel/printk/internal.h b/kernel/printk/internal.h index 655810f2976e..0f2be350600e 100644 --- a/kernel/printk/internal.h +++ b/kernel/printk/internal.h @@ -13,6 +13,12 @@ int devkmsg_sysctl_set_loglvl(struct ctl_table *table, int write, #define printk_sysctl_init() do { } while (0) #endif +#define con_printk(lvl, con, fmt, ...) \ + printk(lvl pr_fmt("%s%sconsole [%s%d] " fmt), \ + (con->flags & CON_NBCON) ? "" : "legacy ", \ + (con->flags & CON_BOOT) ? "boot" : "", \ + con->name, con->index, ##__VA_ARGS__) + #ifdef CONFIG_PRINTK #ifdef CONFIG_PRINTK_CALLER diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 98b4854c81ea..582552a96c57 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -3359,12 +3359,6 @@ static void try_enable_default_console(struct console *newcon) newcon->flags |= CON_CONSDEV; } -#define con_printk(lvl, con, fmt, ...) \ - printk(lvl pr_fmt("%s%sconsole [%s%d] " fmt), \ - (con->flags & CON_NBCON) ? "" : "legacy ", \ - (con->flags & CON_BOOT) ? "boot" : "", \ - con->name, con->index, ##__VA_ARGS__) - static void console_init_seq(struct console *newcon, bool bootcon_registered) { struct console *con; diff --git a/kernel/printk/printk_nbcon.c b/kernel/printk/printk_nbcon.c index b0acde0cb949..39fa64891ec6 100644 --- a/kernel/printk/printk_nbcon.c +++ b/kernel/printk/printk_nbcon.c @@ -5,6 +5,7 @@ #include <linux/kernel.h> #include <linux/console.h> #include <linux/delay.h> +#include <linux/slab.h> #include "internal.h" /* * Printk console printing implementation for consoles that do not depend on @@ -20,6 +21,9 @@ * region and aborts the operation if it detects a takeover. * * In case of panic the nesting context can take over the console forcefully. + * If the interrupted context touches the assigned record buffer after + * takeover, it does not cause harm because the interrupting single panic + * context is assigned its own panic record buffer. * * A concurrent writer on a different CPU with a higher priority can request * to take over the console by: @@ -356,6 +360,8 @@ static int nbcon_context_try_acquire_hostile(struct nbcon_context *ctxt, return 0; } +static struct printk_buffers panic_nbcon_pbufs; + /** * nbcon_context_try_acquire - Try to acquire nbcon console * @ctxt: The context of the caller @@ -372,7 +378,6 @@ static int nbcon_context_try_acquire_hostile(struct nbcon_context *ctxt, __maybe_unused static bool nbcon_context_try_acquire(struct nbcon_context *ctxt) { - __maybe_unused unsigned int cpu = smp_processor_id(); struct console *con = ctxt->console; struct nbcon_state cur; @@ -471,6 +476,13 @@ static bool nbcon_context_try_acquire(struct nbcon_context *ctxt) ctxt->hostile = 0; ctxt->takeover_unsafe = 0; } + + /* Assign the appropriate buffer for this context. */ + if (atomic_read(&panic_cpu) == cpu) + ctxt->pbufs = &panic_nbcon_pbufs; + else + ctxt->pbufs = con->pbufs; + return true; } @@ -509,7 +521,7 @@ static void nbcon_context_release(struct nbcon_context *ctxt) nbcon_state_read(con, &cur); do { if (!nbcon_owner_matches(&cur, cpu, ctxt->prio)) - return; + break; new.atom = cur.atom; new.prio = NBCON_PRIO_NONE; @@ -521,6 +533,8 @@ static void nbcon_context_release(struct nbcon_context *ctxt) */ } while (!nbcon_state_try_cmpxchg(con, &cur, &new)); + + ctxt->pbufs = NULL; } /** @@ -534,6 +548,12 @@ bool nbcon_init(struct console *con) { struct nbcon_state state = { }; + con->pbufs = kmalloc(sizeof(*con->pbufs), GFP_KERNEL); + if (!con->pbufs) { + con_printk(KERN_ERR, con, "failed to allocate printing buffer\n"); + return false; + } + nbcon_state_set(con, &state); return true; } @@ -547,4 +567,6 @@ void nbcon_cleanup(struct console *con) struct nbcon_state state = { }; nbcon_state_set(con, &state); + kfree(con->pbufs); + con->pbufs = NULL; } -- 2.39.2
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