lkml.org 
[lkml]   [2012]   [Jul]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH] kmsg: properly handle concurrent non-blocking read() from /proc/kmsg
    >>> Kay Sievers <kay@vrfy.org> 07/03/12 8:17 PM >>>
    >From: Kay Sievers <kay@vrfy.org>
    >Subject: kmsg: properly handle concurrent non-blocking read() from /proc/kmsg
    >
    >The /proc/kmsg read() interface is internally simply wired up to a sequence
    >of syslog() syscalls, which might are racy between their checks and actions,
    >regarding concurrency.
    >
    >In the (very uncommon) case of concurrent readers of /dev/kmsg, relying on
    >usual O_NONBLOCK behavior, the recently introduced mutex might block an
    >O_NONBLOCK reader in read(), when poll() returns for it, but another process
    >has already read the data in the meantime. We've seen that while running
    >artificial test setups and tools that "fight" about /proc/kmsg data.
    >
    >This restores the original /proc/kmsg behavior, where in case of concurrent
    >read()s, poll() might wake up but the read() syscall will just return 0 to
    >the caller, while another process has "stolen" the data.
    >
    >This is in the general case not the expected behavior, but it is the exact
    >same one, that can easily be triggered with a 3.4 kernel, and some tools
    >might just rely on it.
    >
    >The mutex is not needed, the original integrity issue which introduced it,
    >is in the meantime covered by:
    >"fill buffer with more than a single message for SYSLOG_ACTION_READ"
    >116e90b23f74d303e8d607c7a7d54f60f14ab9f2
    >
    >Cc: Yuanhan Liu <yuanhan.liu@linux.intel.com>
    >Cc: Jan Beulich <JBeulich@suse.com>
    >Signed-off-by: Kay Sievers <kay@vrfy.org>

    This being a revert of all but a single change of
    4a77a5a06ec66ed05199b301e7c25f42f979afdc, which I had suggested to
    be reverted anyway:

    Acked-by: Jan Beulich <jbeulich@suse.com>




    \
     
     \ /
      Last update: 2012-07-04 09:01    [W:0.029 / U:0.100 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site