> -----Original Message----- > From: kernelnewbies-bounce@xxxxxxxxxxxx [mailto:kernelnewbies- > bounce@xxxxxxxxxxxx] On Behalf Of Deepak Joshi > Sent: Thursday, July 21, 2005 6:54 PM > To: kernel mail > Subject: down_read and uninterruptible sleep > > hi all, > > I have one doubt related to down_read semaphore > function. what i read from linux device drivers-3 book > is > > "A newly initialized rwsem is available for the next > task(reader or writer) that comes > along. The interface for code needing read-only access > is: > -- void down_read(struct rw_semaphore *sem); > -- int down_read_trylock(struct rw_semaphore > *sem); > -- void up_read(struct rw_semaphore *sem); > A call to down_read provides read-only access to the > protected resources, possibly concurrently with other > readers. Note that down_read may put the calling > process into an uninterruptible sleep." > > The last statement says that down_read may put the > calling pocess into an uninterruptible sleep. how and > in which conditions it might happen as we are just > reading the shared resource only. An simple e.g. condition is the situation where rwsem is already acquired by some writer using down_write. In that case any down_read call will put the caller in sleep state. HTH Sanjay > > plz help me in clearing this doubt. > > Thanks in advance. > > Deepak Joshi > > > > > > > > > ___________________________________________________________ > Yahoo! Messenger - NEW crystal clear PC to PC calling worldwide with > voicemail http://uk.messenger.yahoo.com > > -- > Kernelnewbies: Help each other learn about the Linux kernel. > Archive: http://mail.nl.linux.org/kernelnewbies/ > FAQ: http://kernelnewbies.org/faq/ -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
