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pstore: Switch pmsg_lock to an rt_mutex to avoid priority inversion
[ Upstream commit76d62f24db
] Wei Wang reported seeing priority inversion caused latencies caused by contention on pmsg_lock, and suggested it be switched to a rt_mutex. I was initially hesitant this would help, as the tasks in that trace all seemed to be SCHED_NORMAL, so the benefit would be limited to only nice boosting. However, another similar issue was raised where the priority inversion was seen did involve a blocked RT task so it is clear this would be helpful in that case. Cc: Wei Wang <wvw@google.com> Cc: Midas Chien<midaschieh@google.com> Cc: Connor O'Brien <connoro@google.com> Cc: Kees Cook <keescook@chromium.org> Cc: Anton Vorontsov <anton@enomsg.org> Cc: Colin Cross <ccross@android.com> Cc: Tony Luck <tony.luck@intel.com> Cc: kernel-team@android.com Fixes:9d5438f462
("pstore: Add pmsg - user-space accessible pstore object") Reported-by: Wei Wang <wvw@google.com> Signed-off-by: John Stultz <jstultz@google.com> Signed-off-by: Kees Cook <keescook@chromium.org> Link: https://lore.kernel.org/r/20221214231834.3711880-1-jstultz@google.com Signed-off-by: Sasha Levin <sashal@kernel.org>
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1 changed files with 4 additions and 3 deletions
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@ -15,9 +15,10 @@
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#include <linux/device.h>
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#include <linux/fs.h>
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#include <linux/uaccess.h>
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#include <linux/rtmutex.h>
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#include "internal.h"
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static DEFINE_MUTEX(pmsg_lock);
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static DEFINE_RT_MUTEX(pmsg_lock);
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static ssize_t write_pmsg(struct file *file, const char __user *buf,
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size_t count, loff_t *ppos)
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@ -36,9 +37,9 @@ static ssize_t write_pmsg(struct file *file, const char __user *buf,
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if (!access_ok(VERIFY_READ, buf, count))
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return -EFAULT;
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mutex_lock(&pmsg_lock);
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rt_mutex_lock(&pmsg_lock);
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ret = psinfo->write_user(&record, buf);
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mutex_unlock(&pmsg_lock);
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rt_mutex_unlock(&pmsg_lock);
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return ret ? ret : count;
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}
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