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    Subject[PATCH v1] kernel/trace:check the val against the available mem
    Date
    It is reported that some user app would like to echo a huge
    number to "/sys/kernel/debug/tracing/buffer_size_kb" regardless
    of the available memory, which will cause the coinstantaneous
    page allocation failed and introduce OOM. The commit checking the
    val against the available mem first to avoid the consequence allocation.

    Signed-off-by: Zhaoyang Huang <zhaoyang.huang@spreadtrum.com>
    ---
    kernel/trace/trace.c | 39 ++++++++++++++++++++++++++++++++++++++-
    1 file changed, 38 insertions(+), 1 deletion(-)

    diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
    index 2d0ffcc..a4a4237 100644
    --- a/kernel/trace/trace.c
    +++ b/kernel/trace/trace.c
    @@ -43,6 +43,8 @@
    #include <linux/trace.h>
    #include <linux/sched/rt.h>

    +#include <linux/mm.h>
    +#include <linux/swap.h>
    #include "trace.h"
    #include "trace_output.h"

    @@ -5967,6 +5969,39 @@ static ssize_t tracing_splice_read_pipe(struct file *filp,
    return ret;
    }

    +static long get_available_mem(void)
    +{
    + struct sysinfo i;
    + long available;
    + unsigned long pagecache;
    + unsigned long wmark_low = 0;
    + unsigned long pages[NR_LRU_LISTS];
    + struct zone *zone;
    + int lru;
    +
    + si_meminfo(&i);
    + si_swapinfo(&i);
    +
    + for (lru = LRU_BASE; lru < NR_LRU_LISTS; lru++)
    + pages[lru] = global_page_state(NR_LRU_BASE + lru);
    +
    + for_each_zone(zone)
    + wmark_low += zone->watermark[WMARK_LOW];
    +
    + available = i.freeram - wmark_low;
    +
    + pagecache = pages[LRU_ACTIVE_FILE] + pages[LRU_INACTIVE_FILE];
    + pagecache -= min(pagecache / 2, wmark_low);
    + available += pagecache;
    +
    + available += global_page_state(NR_SLAB_RECLAIMABLE) -
    + min(global_page_state(NR_SLAB_RECLAIMABLE) / 2, wmark_low);
    +
    + if (available < 0)
    + available = 0;
    + return available;
    +}
    +
    static ssize_t
    tracing_entries_write(struct file *filp, const char __user *ubuf,
    size_t cnt, loff_t *ppos)
    @@ -5975,13 +6010,15 @@ static ssize_t tracing_splice_read_pipe(struct file *filp,
    struct trace_array *tr = inode->i_private;
    unsigned long val;
    int ret;
    + long available;

    + available = get_available_mem();
    ret = kstrtoul_from_user(ubuf, cnt, 10, &val);
    if (ret)
    return ret;

    /* must have at least 1 entry */
    - if (!val)
    + if (!val || (val > available))
    return -EINVAL;

    /* value is in KB */
    --
    1.9.1
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