syzbot is reporting circular locking dependency due to calling printk() with port lock held [1]. When this problem was reported, we worried whether printk_safe context will remain available in future kernels [2], and then this problem was forgotten. But in order to utilize syzbot's resource for finding other bugs/reproducers by closing this one of top crashers, let's apply a patch which counts on availability of printk_safe context.
syzbot is also reporting same dependency due to memory allocation fault injection at tty_buffer_alloc(). Although __GFP_NOWARN cannot prevent memory allocation fault injection from calling printk(), let's use __GFP_NOWARN at tty_buffer_alloc() in addition to using printk_safe context, for generating many lines of messages due to warn_alloc() is annoying. If we want to report it, we can use pr_warn() instead. [1] https://syzkaller.appspot.com/bug?id=39ea6caa479af471183997376dc7e90bc7d64a6a [2] https://lkml.kernel.org/r/20190218054649.GA26686@jagdpanzerIV Reported-by: syzbot <[email protected]> Reported-by: syzbot <[email protected]> Signed-off-by: Tetsuo Handa <[email protected]> Fixes: b6da31b2c07c46f2 ("tty: Fix data race in tty_insert_flip_string_fixed_flag") Cc: <[email protected]> # 4.18+ --- drivers/tty/tty_buffer.c | 5 ++++- include/linux/tty.h | 9 ++++++++- 2 files changed, 12 insertions(+), 2 deletions(-) diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c index 6d4995a5f318..d59f7873bc49 100644 --- a/drivers/tty/tty_buffer.c +++ b/drivers/tty/tty_buffer.c @@ -156,6 +156,7 @@ static struct tty_buffer *tty_buffer_alloc(struct tty_port *port, size_t size) { struct llist_node *free; struct tty_buffer *p; + unsigned long flags; /* Round the buffer size out */ size = __ALIGN_MASK(size, TTYB_ALIGN_MASK); @@ -172,7 +173,9 @@ static struct tty_buffer *tty_buffer_alloc(struct tty_port *port, size_t size) have queued and recycle that ? */ if (atomic_read(&port->buf.mem_used) > port->buf.mem_limit) return NULL; - p = kmalloc(sizeof(struct tty_buffer) + 2 * size, GFP_ATOMIC); + printk_safe_enter_irqsave(flags); + p = kmalloc(sizeof(struct tty_buffer) + 2 * size, GFP_ATOMIC | __GFP_NOWARN); + printk_safe_exit_irqrestore(flags); if (p == NULL) return NULL; diff --git a/include/linux/tty.h b/include/linux/tty.h index 95fc2f100f12..7ae8eb46fec3 100644 --- a/include/linux/tty.h +++ b/include/linux/tty.h @@ -14,6 +14,7 @@ #include <uapi/linux/tty.h> #include <linux/rwsem.h> #include <linux/llist.h> +#include <../../kernel/printk/internal.h> /* @@ -773,7 +774,13 @@ static inline void proc_tty_unregister_driver(struct tty_driver *d) {} #endif #define tty_msg(fn, tty, f, ...) \ - fn("%s %s: " f, tty_driver_name(tty), tty_name(tty), ##__VA_ARGS__) + do { \ + unsigned long flags; \ + \ + printk_safe_enter_irqsave(flags); \ + fn("%s %s: " f, tty_driver_name(tty), tty_name(tty), ##__VA_ARGS__); \ + printk_safe_exit_irqrestore(flags); \ + } while (0) #define tty_debug(tty, f, ...) tty_msg(pr_debug, tty, f, ##__VA_ARGS__) #define tty_info(tty, f, ...) tty_msg(pr_info, tty, f, ##__VA_ARGS__) -- 2.18.4
