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U2FsdGVkX1+wBORAGHsFlxSR/mAbyoV68GaWuUg81EmfnUrk0Npd6ePHq3TB827zZBMZ9d/MfiCHhUgymJBM2VOvJ1htRC+MpTPyl15c9C4Wv3DKeokXTU8J+9uH04Ey1NN7E2/Rh7SmQ+0cs3SmKkMDkqwHkqUJI9OOT4VyzjLvQ5bxOkAylJcET7bpb8z2SpJdC9ELUKG5K4DXNbmrO00+KrULG2HZdngGBM5xNdLfo4PF6DM/EAI0bRCcO0lltwuNqy2MPEr38E9FLtsqlemKK6sS3VLRkxkrSqveiigyLiKYO6ufJyDNzIjKMAoQUCficrf6rcWiT1BwS9vldWd/FH7LvGwOk0WzyenpR+8T8tY89ygabNHLEBrFj56ngX+5bJ6mwnB2gzgWuG4f4ZPqKiUraeYTKrbUkoB4U5h09z6LO2Eq0f2OMGZ93LY9ZmStdbKj4PpTcJDeblbJjY3AcpSpKt3fIxaB360hhiBMetaloje3bcW0+57rgpyOyE6VA9+sFf3uxCwbRlmRgdFsfQ3XBcAn0SjyIwGiKPIRR4u7jqKE7g7mHhVPVszDdTzjEgNY2Du1QIuoYcke5rBnFwFjF43Wp/8OytnjCeu7HPcnJMsX2OsRWa3KJ5+ocTYMuSNV0bnz6+xwambsIN4NojxU4M9t2nIF6FyAh0ZvsnbSqK0p7N1yrhbfQOlJhCRG0poRMZOG+p8bFIrZ1FNBfLVG9yxt0VJyhZ+JMstUNtESPBHALvOOUC+OhtHT52MHdzJSjun5nbx5yNCKmbaFZdZs1E5nq5Od/x+MO/9GcwU/j07x4eyNWH26KIF/UklbZdr5omWqr5EA8Z8m7s2YwPD6r/0XE4RrvRNtBFcojpAihEFrPC1QSoMrKXY/GTOMWg1VPKW4YouLaUUhQzcgrjYeGjU8fB0ltFy/kstpIvgsugWfl+JfbGrQA9JeNwtHSjGW/4QEL0v26ur W0CjKFs3 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 19 Feb 2026, at 18:36, Kalesh Singh wrote: > The rss_stat trace event allows userspace tools, like Perfetto [1], > to inspect per-process RSS metric changes over time. > > The curr field was introduced to rss_stat in commit e4dcad204d3a > ("rss_stat: add support to detect RSS updates of external mm"). > It's intent is to indicate whether the RSS update is for the > mm_struct of the current execution context; and is set to false > when operating on a remote mm_struct (e.g., via kswapd or a > direct reclaimer). > > However, an issue arises when a kernel thread temporarily adopts > a user process's mm_struct. Kernel threads do not have their own > mm_struct and normally have current->mm set to NULL. To operate > on user memory, they can "borrow" a memory context using > kthread_use_mm(), which sets current->mm to the user process's mm. > > This can be observed, for example, in the USB Function Filesystem > (FFS) driver. The ffs_user_copy_worker() handles AIO completions > and uses kthread_use_mm() to copy data to a user-space buffer. > If a page fault occurs during this copy, the fault handler executes > in the kthread's context. > > At this point, current is the kthread, but current->mm points to the > user process's mm. Since the rss_stat event (from the page fault) > is for that same mm, the condition current->mm == mm becomes true, > causing curr to be incorrectly set to true when the trace event is > emitted. > > This is misleading because it suggests the mm belongs to the kthread, > confusing userspace tools that track per-process RSS changes and > corrupting their mm_id-to-process association. > > Fix this by ensuring curr is always false when the trace event is > emitted from a kthread context by checking for the PF_KTHREAD flag. > > [1] https://perfetto.dev/ > > Fixes: e4dcad204d3a ("rss_stat: add support to detect RSS updates of external mm") > Cc: Andrew Morton > Cc: "David Hildenbrand (Arm)" > Cc: Joel Fernandes > Cc: Lorenzo Stoakes > Cc: Minchan Kim > Cc: Steven Rostedt > Cc: Suren Baghdasaryan > Signed-off-by: Kalesh Singh > --- > include/trace/events/kmem.h | 8 +++++++- > 1 file changed, 7 insertions(+), 1 deletion(-) > LGTM. Acked-by: Zi Yan Best Regards, Yan, Zi